feat(checker): add mean method on frames

gen/midas.py

@@ -152,4 +152,14 @@ class FunctionType:
         required: bool
 
 
+class FrameType:
+    columns: list[Column]
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        location: Optional[Location] = None
+        name: Token
+        type: Type
+
+
 ###<

midas/ast/midas.py

@@ -253,6 +253,9 @@ class Type(ABC):
         @abstractmethod
         def visit_function_type(self, type: FunctionType) -> T: ...
 
+        @abstractmethod
+        def visit_frame_type(self, type: FrameType) -> T: ...
+
 
 @dataclass(frozen=True)
 class NamedType(Type):
@@ -311,3 +314,17 @@ class FunctionType(Type):
 
     def accept(self, visitor: Type.Visitor[T]) -> T:
         return visitor.visit_function_type(self)
+
+
+@dataclass(frozen=True)
+class FrameType(Type):
+    columns: list[Column]
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        location: Optional[Location] = None
+        name: Token
+        type: Type
+
+    def accept(self, visitor: Type.Visitor[T]) -> T:
+        return visitor.visit_frame_type(self)

midas/ast/printer.py

@@ -350,6 +350,25 @@ class MidasAstPrinter(
                 arg.type.accept(self)
             self._write_line(f"required: {arg.required}", last=True)
 
+    def visit_frame_type(self, type: m.FrameType) -> None:
+        self._write_line("FrameType")
+        with self._child_level(single=True):
+            self._write_line("columns")
+            with self._child_level():
+                for i, column in enumerate(type.columns):
+                    self._idx = i
+                    if i == len(type.columns) - 1:
+                        self._mark_last()
+                    self._print_frame_column(column)
+
+    def _print_frame_column(self, column: m.FrameType.Column) -> None:
+        self._write_line("Column")
+        with self._child_level():
+            self._write_line(f'name: "{column.name.lexeme}"')
+            self._write_line("type")
+            with self._child_level(single=True):
+                column.type.accept(self)
+
 
 class MidasPrinter(m.Expr.Visitor[str], m.Stmt.Visitor[str], m.Type.Visitor[str]):
     def __init__(self, indent: int = 4):
@@ -502,6 +521,23 @@ class MidasPrinter(m.Expr.Visitor[str], m.Stmt.Visitor[str], m.Type.Visitor[str]
             res += "?"
         return res
 
+    def visit_frame_type(self, type: m.FrameType) -> str:
+        res: str = self.indented("Frame[")
+        if len(type.columns) != 0:
+            res += "\n"
+            self.level += 1
+            columns: list[str] = []
+            for column in type.columns:
+                columns.append(self.indented(self._print_frame_column(column)))
+            res += ",\n".join(columns)
+            self.level -= 1
+            res += "\n"
+        res += "]"
+        return res
+
+    def _print_frame_column(self, column: m.FrameType.Column) -> str:
+        return f"{column.name.lexeme}: {column.type.accept(self)}"
+
 
 class PythonAstPrinter(
     AstPrinter,

midas/checker/frame_methods.py

@@ -0,0 +1,198 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Any, Callable, Optional
+
+from midas.ast.location import Location
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import (
+    ColumnType,
+    DataFrameType,
+    Function,
+    OverloadedFunction,
+    TopType,
+    Type,
+    UnknownType,
+    unfold_type,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import PythonTyper, TypedExpr
+
+
+@staticmethod
+def frame_method(*names: str):
+    def wrapper(func):
+        names_: tuple[str, ...] = names
+        if len(names_) == 0:
+            names_ = (func.__name__,)
+        setattr(func, "__method_names__", names_)
+        return func
+
+    return wrapper
+
+
+@dataclass(frozen=True, kw_only=True)
+class Call:
+    location: Location
+    frame: DataFrameType
+    positional: list[TypedExpr]
+    keywords: dict[str, TypedExpr]
+
+
+class _MethodRegistryMeta(type):
+    _methods: dict[str, Callable] = {}
+
+    def __new__(
+        cls,
+        name: str,
+        bases: tuple[type, ...],
+        namespace: dict[str, Any],
+    ):
+        new_class = super().__new__(cls, name, bases, namespace)
+        new_class._methods = {}
+        for attr in namespace.values():
+            if callable(attr) and hasattr(attr, "__method_names__"):
+                for name in attr.__method_names__:  # type: ignore
+                    new_class._methods[name] = attr
+        return new_class
+
+
+class MethodRegistry(metaclass=_MethodRegistryMeta):
+    def __init__(self, typer: PythonTyper) -> None:
+        self.typer: PythonTyper = typer
+
+    @property
+    def reporter(self) -> FileReporter:
+        return self.typer.reporter
+
+    @property
+    def types(self) -> TypesRegistry:
+        return self.typer.types
+
+    def call(
+        self,
+        method: str,
+        call: Call,
+    ) -> Type:
+        func: Optional[Callable] = self._methods.get(method)
+        if func is None:
+            self.reporter.error(call.location, f"Unknown method {method}")
+            return UnknownType()
+        return func(self, call)
+
+    @frame_method("add", "__add__")
+    def add(
+        self,
+        call: Call,
+    ) -> Type:
+        # TODO: support add with scalar, sequence, Series, dict
+        # TODO: check operation exists on inner column types
+
+        new_columns: list[DataFrameType.Column] = []
+
+        by_name: dict[str, DataFrameType.Column] = {}
+        frame2: Optional[DataFrameType] = None
+        if len(call.positional) != 0:
+            other: Type = call.positional[0][1]
+            unfolded_other: Type = unfold_type(other)
+            if isinstance(unfolded_other, DataFrameType):
+                frame2 = unfolded_other
+                by_name = {
+                    col.name: col for col in frame2.columns if col.name is not None
+                }
+
+        in_frame1: set[str] = set()
+        for column in call.frame.columns:
+            if column.name is not None:
+                in_frame1.add(column.name)
+
+            col_type1: Type = column.type
+            col_type: Type = ColumnType(type=UnknownType())
+            if column.name in by_name:
+                column2 = by_name[column.name]
+                col_type2: Type = column2.type
+                if self.types.are_equivalent(col_type2, col_type1):
+                    col_type = col_type1
+
+            new_column = DataFrameType.Column(
+                index=column.index,
+                name=column.name,
+                type=col_type,
+            )
+            new_columns.append(new_column)
+
+        if frame2 is not None:
+            for column in frame2.columns:
+                if column.name in in_frame1:
+                    continue
+                new_columns.append(
+                    DataFrameType.Column(
+                        index=len(new_columns),
+                        name=column.name,
+                        type=ColumnType(type=UnknownType()),
+                    )
+                )
+
+        signature = Function(
+            args=[
+                Function.Argument(
+                    pos=0,
+                    name="other",
+                    type=DataFrameType(columns=[]),
+                    required=True,
+                ),
+            ],
+            returns=DataFrameType(columns=new_columns),
+        )
+
+        return (
+            self.typer._get_call_result(
+                location=call.location,
+                callee=signature,
+                positional=call.positional,
+                keywords=call.keywords,
+            )
+            or UnknownType()
+        )
+
+    @frame_method()
+    def mean(self, call: Call) -> Type:
+        with_axis = Function(
+            kw_args=[
+                Function.Argument(
+                    pos=0,
+                    name="axis",
+                    type=self.types.get_type("int"),
+                    required=False,
+                )
+            ],
+            returns=ColumnType(type=TopType()),
+        )
+        without_axis = Function(
+            kw_args=[
+                Function.Argument(
+                    pos=0,
+                    name="axis",
+                    type=self.types.get_type("None"),
+                    required=True,
+                )
+            ],
+            returns=TopType(),
+        )
+        overload = OverloadedFunction(
+            overloads=[
+                with_axis,
+                without_axis,
+            ]
+        )
+        return (
+            self.typer._get_call_result(
+                location=call.location,
+                callee=overload,
+                positional=call.positional,
+                keywords=call.keywords,
+            )
+            or UnknownType()
+        )

midas/checker/frames.py

@@ -0,0 +1,154 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Optional, TypeGuard, cast
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.frame_methods import Call, MethodRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import ColumnType, DataFrameType, TupleType, Type, UnknownType
+
+if TYPE_CHECKING:
+    from midas.checker.python import PythonTyper, TypedExpr
+
+
+def is_list_of_literals(exprs: list[p.Expr]) -> TypeGuard[list[p.LiteralExpr]]:
+    return all(isinstance(expr, p.LiteralExpr) for expr in exprs)
+
+
+class FrameManager:
+    def __init__(self, typer: PythonTyper) -> None:
+        self.typer: PythonTyper = typer
+        self.method_resolver: MethodRegistry = MethodRegistry(self.typer)
+
+    def assign(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        index: p.Expr,
+        value_type: Type,
+    ) -> Type:
+        match index:
+            case p.LiteralExpr(value=str() as name):
+                return self.assign_column(reporter, location, frame, name, value_type)
+
+            case p.ListExpr(items=indices) if is_list_of_literals(indices) and all(
+                isinstance(idx, str) for idx in indices
+            ):
+                raise NotImplementedError
+
+            case _:
+                reporter.error(location, f"Invalid index type {index} on {frame}")
+                return UnknownType()
+
+    def assign_column(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        name: str,
+        type: Type,
+    ) -> Type:
+        if not isinstance(type, ColumnType):
+            reporter.error(
+                location,
+                f"Cannot assign {type} to dataframe column. Must be a ColumnType",
+            )
+            return frame
+        return self._set_column(frame, name, type)
+
+    def get(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        index: p.Expr,
+    ) -> Type:
+        match index:
+            case p.LiteralExpr(value=str() as name):
+                column: Optional[ColumnType] = FrameManager._get_column(frame, name)
+                if column is None:
+                    reporter.error(location, f"Unknown column '{name}' on {frame}")
+                    return UnknownType()
+                return column
+
+            case p.ListExpr(items=indices) if is_list_of_literals(indices) and all(
+                isinstance(index.value, str) for index in indices
+            ):
+                names: list[str] = [cast(str, index.value) for index in indices]
+                columns: list[ColumnType] = []
+                for name in names:
+                    column: Optional[ColumnType] = FrameManager._get_column(frame, name)
+                    if column is None:
+                        reporter.error(location, f"Unknown column '{name}' on {frame}")
+                        return UnknownType()
+                    columns.append(column)
+                return TupleType(items=tuple(columns))
+
+            case _:
+                reporter.error(location, f"Invalid index type {index} on {frame}")
+                return UnknownType()
+
+    @classmethod
+    def _set_column(
+        cls, frame: DataFrameType, name: str, column: ColumnType
+    ) -> DataFrameType:
+        new_columns: list[DataFrameType.Column] = []
+        index: int = len(frame.columns)
+        replace: bool = False
+        for i, col in enumerate(frame.columns):
+            if col.name == name:
+                index = i
+                replace = True
+                # TODO: check column type here to prevent changing it
+            new_columns.append(col)
+
+        new_col: DataFrameType.Column = DataFrameType.Column(
+            index=index,
+            name=name,
+            type=column,
+        )
+        if replace:
+            new_columns[index] = new_col
+        else:
+            new_columns.append(new_col)
+
+        return DataFrameType(columns=new_columns)
+
+    @classmethod
+    def _set_columns(
+        cls, frame: DataFrameType, names: list[str], columns: list[ColumnType]
+    ) -> DataFrameType:
+        for name, col in zip(names, columns):
+            frame = cls._set_column(frame, name, col)
+        return frame
+
+    @classmethod
+    def _get_column(cls, frame: DataFrameType, name: str) -> Optional[ColumnType]:
+        for col in frame.columns:
+            if col.name == name:
+                return col.type
+        return None
+
+    @classmethod
+    def _get_columns(
+        cls, frame: DataFrameType, names: list[str]
+    ) -> list[Optional[ColumnType]]:
+        return [cls._get_column(frame, name) for name in names]
+
+    def call(
+        self,
+        method: str,
+        location: Location,
+        frame: DataFrameType,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Type:
+        call: Call = Call(
+            location=location,
+            frame=frame,
+            positional=positional,
+            keywords=keywords,
+        )
+        return self.method_resolver.call(method, call)

midas/checker/midas.py

@@ -14,8 +14,10 @@ from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.types import (
     AliasType,
     AppliedType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
     ExtensionType,
     Function,
     GenericType,
@@ -401,6 +403,18 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             kw=[process_arg(arg, i + n_pos + n_mixed) for i, arg in enumerate(spec.kw)],
         )
 
+    def visit_frame_type(self, type: m.FrameType) -> Type:
+        def process_column(i: int, col: m.FrameType.Column) -> DataFrameType.Column:
+            return DataFrameType.Column(
+                index=i,
+                name=col.name.lexeme,
+                type=ColumnType(type=col.type.accept(self)),
+            )
+
+        return DataFrameType(
+            columns=[process_column(i, col) for i, col in enumerate(type.columns)]
+        )
+
     def _resolve_type_params(self, params: list[m.TypeParam]):
         vars: list[TypeVar] = []
         for param in params:

midas/checker/python.py

@@ -8,6 +8,7 @@ from midas.ast.location import Location
 from midas.ast.printer import MidasPrinter
 from midas.checker.environment import Environment
 from midas.checker.evaluator import Evaluator
+from midas.checker.frames import FrameManager
 from midas.checker.operators import (
     PY_COMPARATOR_METHODS,
     PY_OPERATOR_METHODS,
@@ -21,10 +22,13 @@ from midas.checker.types import (
     AliasType,
     AppliedType,
     BaseType,
+    ColumnType,
     ConstraintType,
+    DataFrameType,
     Function,
     GenericType,
     OverloadedFunction,
+    TupleType,
     Type,
     TypeVar,
     UnitType,
@@ -43,6 +47,10 @@ class ReturnException(Exception):
     pass
 
 
+class UndefinedMethodException(Exception):
+    pass
+
+
 @dataclass(frozen=True, kw_only=True)
 class MappedArgument:
     expr: p.Expr
@@ -71,6 +79,7 @@ class PythonTyper(
         self.logger: logging.Logger = logging.getLogger("PythonTyper")
         self.reporter: FileReporter = reporter.for_file(None)
         self.types: TypesRegistry = types
+        self.frame_mgr: FrameManager = FrameManager(self)
         self.global_env: Environment = Preamble(self.types)
         self.env: Environment = self.global_env
         self.locals: dict[p.Expr, int] = {}
@@ -190,6 +199,36 @@ class PythonTyper(
             return self.env.get_at(distance, name)
         return self.global_env.get(name)
 
+    def call_method(
+        self,
+        location: Location,
+        obj: Type,
+        method_name: str,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Optional[Type]:
+        unfolded: Type = unfold_type(obj)
+        match unfolded:
+            case DataFrameType():
+                return self.frame_mgr.call(
+                    method=method_name,
+                    location=location,
+                    frame=unfolded,
+                    positional=positional,
+                    keywords=keywords,
+                )
+
+        method: Optional[Type] = self.types.lookup_member(obj, method_name)
+        if method is None:
+            raise UndefinedMethodException
+
+        return self._get_call_result(
+            location,
+            method,
+            positional,
+            keywords,
+        )
+
     def is_subtype(self, type1: Type, type2: Type) -> bool:
         return self.types.is_subtype(type1, type2)
 
@@ -319,9 +358,15 @@ class PythonTyper(
             case p.VariableExpr():
                 self._assign_var(location, target, value_type)
 
+            # Allow any kind of object because we disallow creating new attributes
             case p.GetExpr(object=object, name=name):
                 self._assign_attr(location, object, name, value_type)
 
+            # Only support variable expressions because modifying
+            # the underlying value would require reference types
+            case p.SubscriptExpr(object=p.VariableExpr() as var, index=index):
+                self._assign_sub(location, var, index, value_type)
+
             case _:
                 if not isinstance(target, p.VariableExpr):
                     self.logger.warning(f"Unsupported assignment to {target}")
@@ -360,6 +405,27 @@ class PythonTyper(
                 f"Cannot assign {value_type} to member '{object_type}.{name}' of type {member}",
             )
 
+    def _assign_sub(
+        self,
+        location: Location,
+        var: p.VariableExpr,
+        index: p.Expr,
+        value_type: Type,
+    ):
+        var_type: Type = self.type_of(var)
+        # TODO: what happens if type is an alias of a dataframe type
+        match var_type:
+            case DataFrameType() as frame:
+                new_type: Type = self.frame_mgr.assign(
+                    self.reporter, location, frame, index, value_type
+                )
+                self.env.assign(var.name, new_type)
+            case _:
+                self.reporter.error(
+                    location,
+                    f"Cannot assign {value_type} to index {index} of {var_type}",
+                )
+
     def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
         type: Type = self.type_of(stmt.value) if stmt.value is not None else UnitType()
         self.env.return_types.append(type)
@@ -436,20 +502,16 @@ class PythonTyper(
         left: Type = self.type_of(left_expr)
         right: Type = self.type_of(right_expr)
 
-        operation: Optional[Type] = self.types.lookup_member(left, method)
+        result: Optional[Type]
-        if operation is None:
+        try:
+            result = self.call_method(location, left, method, [(right_expr, right)], {})
+        except UndefinedMethodException:
             self.reporter.error(
                 location,
                 f"Undefined operation {method} between {left} and {right}",
             )
             return UnknownType()
 
-        result: Optional[Type] = self._get_call_result(
-            location,
-            operation,
-            [(right_expr, right)],
-            {},
-        )
         return result or UnknownType()
 
     def visit_unary_expr(self, expr: p.UnaryExpr) -> Type:
@@ -462,20 +524,17 @@ class PythonTyper(
             return UnknownType()
 
         operand: Type = self.type_of(expr.right)
-        operation: Optional[Type] = self.types.lookup_member(operand, method)
+
-        if operation is None:
+        result: Optional[Type]
+        try:
+            result = self.call_method(expr.location, operand, method, [], {})
+        except UndefinedMethodException:
             self.reporter.error(
                 expr.location,
                 f"Undefined operation {method} for {operand}",
             )
             return UnknownType()
 
-        result: Optional[Type] = self._get_call_result(
-            expr.location,
-            operation,
-            [],
-            {},
-        )
         return result or UnknownType()
 
     def visit_call_expr(self, expr: p.CallExpr) -> Type:
@@ -483,13 +542,27 @@ class PythonTyper(
             case p.VariableExpr(name="TypeVar"):
                 return self.define_typevar(expr) or UnknownType()
 
-        callee: Type = self.type_of(expr.callee)
         positional: list[TypedExpr] = [
             (arg, self.type_of(arg)) for arg in expr.arguments
         ]
         keywords: dict[str, TypedExpr] = {
             name: (arg, self.type_of(arg)) for name, arg in expr.keywords.items()
         }
+
+        match expr.callee:
+            case p.GetExpr(object=obj, name=method):
+                obj_type: Type = self.type_of(obj)
+                unfolded: Type = unfold_type(obj_type)
+                if isinstance(unfolded, DataFrameType):
+                    return self.frame_mgr.call(
+                        method,
+                        expr.location,
+                        unfolded,
+                        positional,
+                        keywords,
+                    )
+
+        callee: Type = self.type_of(expr.callee)
         return (
             self._get_call_result(
                 location=expr.location,
@@ -521,6 +594,8 @@ class PythonTyper(
                 return self.types.get_type("float")
             case str():
                 return self.types.get_type("str")
+            case None:
+                return self.types.get_type("None")
             case _:
                 self.reporter.warning(expr.location, f"Unknown literal {expr}")
                 return UnknownType()
@@ -594,7 +669,7 @@ class PythonTyper(
             return self.types.apply_generic(list_type, [item_type])
         self.reporter.error(
             expr.location,
-            f"Heterogeneous list items: {item_types}",
+            f"Heterogeneous list items: [{', '.join(map(str, item_types))}]",
         )
         return self.types.apply_generic(list_type, [UnknownType()])
 
@@ -626,7 +701,7 @@ class PythonTyper(
         else:
             self.reporter.error(
                 expr.location,
-                f"Heterogeneous dict keys: {key_types}",
+                f"Heterogeneous dict keys: [{', '.join(map(str, key_types))}]",
             )
 
         if len(value_types) == 1:
@@ -634,12 +709,19 @@ class PythonTyper(
         else:
             self.reporter.error(
                 expr.location,
-                f"Heterogeneous dict values: {value_types}",
+                f"Heterogeneous dict values: [{', '.join(map(str, value_types))}]",
             )
         return self.types.apply_generic(dict_type, [key_type, value_type])
 
     def visit_subscript_expr(self, expr: p.SubscriptExpr) -> Type:
         object: Type = self.type_of(expr.object)
+        unfolded: Type = unfold_type(object)
+        match unfolded:
+            case TupleType():
+                return self._visit_tuple_subscript(unfolded, expr)
+            case DataFrameType():
+                return self._visit_frame_subscript(unfolded, expr)
+
         operation: Optional[Type] = self.types.lookup_member(object, "__getitem__")
         if operation is None:
             self.reporter.error(
@@ -677,13 +759,26 @@ class PythonTyper(
         self.reporter.warning(node.location, "ConstraintType not yet supported")
         return UnknownType()
 
-    def visit_frame_column(self, node: p.FrameColumn) -> Type:
+    def visit_frame_column(self, node: p.FrameColumn) -> ColumnType:
-        self.reporter.warning(node.location, "FrameColumn not yet supported")
+        return ColumnType(
-        return UnknownType()
+            type=(
+                self.resolve_type_expr(node.type)
+                if node.type is not None
+                else UnknownType()
+            )
+        )
 
     def visit_frame_type(self, node: p.FrameType) -> Type:
-        self.reporter.warning(node.location, "FrameType not yet supported")
+        return DataFrameType(
-        return UnknownType()
+            columns=[
+                DataFrameType.Column(
+                    index=i,
+                    name=column.name,
+                    type=self.visit_frame_column(column),
+                )
+                for i, column in enumerate(node.columns)
+            ]
+        )
 
     def _get_call_result(
         self,
@@ -1216,3 +1311,23 @@ class PythonTyper(
                     expr.location, f"Cannot evaluate cast to {target_type} statically"
                 )
                 return False
+
+    def _visit_tuple_subscript(self, tup: TupleType, expr: p.SubscriptExpr) -> Type:
+        match expr.index:
+            case p.LiteralExpr(value=int() as index):
+                if index < 0 or index >= len(tup.items):
+                    self.reporter.error(
+                        expr.location, f"Index {index} out of range for tuple {tup}"
+                    )
+                    return UnknownType()
+                return tup.items[index]
+            case _:
+                self.reporter.error(
+                    expr.location, f"Invalid index type {expr.index} on {tup}"
+                )
+                return UnknownType()
+
+    def _visit_frame_subscript(
+        self, frame: DataFrameType, expr: p.SubscriptExpr
+    ) -> Type:
+        return self.frame_mgr.get(self.reporter, expr.location, frame, expr.index)

midas/checker/registry.py

@@ -8,8 +8,10 @@ from midas.checker.types import (
     AliasType,
     AppliedType,
     BaseType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
     ExtensionType,
     Function,
     GenericType,
@@ -157,6 +159,24 @@ class TypesRegistry:
                         return False
                 return True
 
+            case (DataFrameType(columns=columns1), DataFrameType(columns=columns2)):
+                # TODO: check order?
+                by_name1: dict[str, DataFrameType.Column] = {
+                    col.name: col for col in columns1 if col.name is not None
+                }
+                for col2 in columns2:
+                    if col2.name not in by_name1:
+                        return False
+                    if not self.is_subtype(by_name1[col2.name].type, col2.type):
+                        return False
+                return True
+
+            case (ColumnType(type=inner1), ColumnType(type=inner2)):
+                # TODO: invariant, replace ColumnType with simple GenericType
+                if not self.are_equivalent(inner1, inner2):
+                    return False
+                return True
+
             case (Function(), Function()):
                 return self.is_func_subtype(type1, type2)
 
@@ -187,6 +207,9 @@ class TypesRegistry:
 
         return False
 
+    def are_equivalent(self, type1: Type, type2: Type) -> bool:
+        return self.is_subtype(type1, type2) and self.is_subtype(type2, type1)
+
     # TODO: verify the logic in here
     def is_func_subtype(self, func1: Function, func2: Function) -> bool:
         """Check whether a function is a subtype of another

midas/checker/resolver.py

@@ -128,6 +128,10 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
             case p.GetExpr():
                 target.accept(self)
+
+            case p.SubscriptExpr():
+                target.accept(self)
+
             case _:
                 raise Exception(f"Unsupported assignment to {target}")
 

midas/checker/types.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 from enum import StrEnum
-from typing import Optional, assert_never
+from typing import Optional, assert_never, cast
 
 import midas.ast.midas as m
 from midas.ast.printer import MidasPrinter
@@ -156,6 +156,37 @@ class ConstraintType:
         return f"{self.type} where {printer.print(self.constraint)}"
 
 
+@dataclass(frozen=True, kw_only=True)
+class TupleType:
+    items: tuple[Type, ...]
+
+    def __str__(self) -> str:
+        return f"({', '.join(map(str, self.items))})"
+
+
+@dataclass(frozen=True, kw_only=True)
+class ColumnType:
+    type: Type
+
+    def __str__(self) -> str:
+        return f"Column[{self.type}]"
+
+
+@dataclass(frozen=True, kw_only=True)
+class DataFrameType:
+    columns: list[Column]
+
+    def __str__(self) -> str:
+        schema: list[str] = [f"{col.name}: {col.type}" for col in self.columns]
+        return f"Frame[{', '.join(schema)}]"
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        index: int
+        name: Optional[str]
+        type: ColumnType
+
+
 def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
     def sub_argument(arg: Function.Argument):
         return Function.Argument(
@@ -165,6 +196,13 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
             required=arg.required,
         )
 
+    def sub_column(col: DataFrameType.Column):
+        return DataFrameType.Column(
+            index=col.index,
+            name=col.name,
+            type=cast(ColumnType, substitute_typevars(col.type, substitutions)),
+        )
+
     match type:
         case TopType():
             return type
@@ -250,10 +288,26 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
                 body=substitute_typevars(body, substitutions),
             )
 
+        case TupleType(items=items):
+            return TupleType(
+                items=tuple(substitute_typevars(item, substitutions) for item in items),
+            )
+
+        case ColumnType(type=items_type):
+            return ColumnType(
+                type=substitute_typevars(items_type, substitutions),
+            )
+
+        case DataFrameType(columns=columns):
+            return DataFrameType(
+                columns=list(map(sub_column, columns)),
+            )
+
         case UnknownType() | UnitType():
             return type
 
         case TopType() | GenericType():
+
             raise NotImplementedError(f"Unsupported type {type}")
 
         # Ensure exhaustiveness
@@ -317,6 +371,15 @@ def to_annotation(type: Type) -> str:
         case ConstraintType():
             return str(type)
 
+        case TupleType(items=items):
+            return f"Tuple[{', '.join(map(to_annotation, items))}]"
+
+        case ColumnType():
+            return "pd.Series"
+
+        case DataFrameType():
+            return "pd.DataFrame"
+
         case _:
             assert_never(type)
 
@@ -342,4 +405,7 @@ Type = (
     | GenericType
     | AppliedType
     | ConstraintType
+    | TupleType
+    | ColumnType
+    | DataFrameType
 )

midas/cli/highlighter.py

@@ -350,6 +350,14 @@ class MidasHighlighter(
         for param in spec.pos + spec.mixed + spec.kw:
             param.type.accept(self)
 
+    def visit_frame_type(self, type: m.FrameType) -> None:
+        self.wrap(type, "frame")
+        for column in type.columns:
+            self._visit_frame_column(column)
+
+    def _visit_frame_column(self, column: m.FrameType.Column) -> None:
+        self.wrap(column, "column")
+
 
 class DiagnosticsHighlighter(Highlighter):
     EXTRA_CSS_PATH: Optional[Path] = Path(__file__).parent / "hl_diagnostic.css"

midas/cli/utils.py

@@ -68,7 +68,7 @@ class DiagnosticPrinter:
 
         loc: Location = diagnostic.location
         if loc.lineno != loc.end_lineno:
-            print(diagnostic)
+            self.print_multiline(lines, diagnostic, indent)
             return
 
         start_offset: int = loc.col_offset
@@ -95,3 +95,27 @@ class DiagnosticPrinter:
         print(indent_str + before + subject + after)
         print(indent_str + cursor)
         print()
+
+    def print_multiline(
+        self, all_lines: list[str], diagnostic: Diagnostic, indent: int = 4
+    ):
+        loc: Location = diagnostic.location
+        lines: list[str] = all_lines[loc.lineno - 1 : loc.end_lineno]
+
+        start_offset: int = loc.col_offset
+        end_offset: int = loc.end_col_offset or (start_offset + 1)
+
+        indent_str: str = " " * indent
+        color: int = self.COLORS.get(diagnostic.type, Ansi.WHITE)
+        res: str = indent_str + lines[0][:start_offset]
+        res += Ansi.FG(color) + lines[0][start_offset:]
+        for line in lines[1:-1]:
+            res += "\n" + indent_str + line
+        res += "\n" + indent_str + lines[-1][:end_offset]
+        res += Ansi.RESET + lines[-1][end_offset:]
+
+        print(diagnostic.location_str + ":")
+        print(res)
+        print()
+        print(Ansi.FG(color) + diagnostic.message + Ansi.RESET)
+        print()

midas/generator/generator.py

@@ -1,4 +1,5 @@
 import ast
+import logging
 import shutil
 from dataclasses import dataclass, field
 from pathlib import Path
@@ -13,13 +14,16 @@ from midas.checker.types import (
     AliasType,
     AppliedType,
     BaseType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
     ExtensionType,
     Function,
     GenericType,
     OverloadedFunction,
     TopType,
+    TupleType,
     Type,
     TypeVar,
     UnitType,
@@ -40,6 +44,7 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
         self.workdir: Path = workdir.resolve()
         self.build_dir: Path = self.workdir / "build" / "midas"
         self.rel_src_path: Path = Path()
+        self.logger: logging.Logger = logging.getLogger("Generator")
 
         self._typed_ast: TypedAST = TypedAST(
             stmts=[],
@@ -332,6 +337,19 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
                 if bound is not None:
                     self._make_cast_asserts(src_location, expr, bound)
 
+            case TupleType(items=items):
+                self._add_assert(
+                    ast.Call(
+                        func=ast.Name(id="isinstance"),
+                        args=[expr, ast.Name(id="tuple")],
+                        keywords=[],
+                    ),
+                    self._make_cast_assert_message(src_location, expr, type),
+                )
+                assert isinstance(expr, ast.Tuple)
+                for item, item_type in zip(expr.elts, items):
+                    self._make_cast_asserts(src_location, item, item_type)
+
             case (
                 TopType()
                 | Function()
@@ -339,8 +357,10 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
                 | ComplexType()
                 | ExtensionType()
                 | GenericType()
+                | ColumnType()
+                | DataFrameType()
             ):
-                raise NotImplementedError(f"Can't make assertion for type {type}")
+                self.logger.warning(f"Can't make assertion for type {type}")
 
             # Ensure exhaustiveness
             case _:

midas/generator/stubs.py

@@ -7,13 +7,16 @@ from midas.checker.types import (
     AliasType,
     AppliedType,
     BaseType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
     ExtensionType,
     Function,
     GenericType,
     OverloadedFunction,
     TopType,
+    TupleType,
     Type,
     TypeVar,
     UnitType,
@@ -30,6 +33,7 @@ class StubsGenerator:
         self.types: TypesRegistry = types
         self.stubs: list[ast.stmt] = []
         self.typing_imports: set[str] = set()
+        self.import_pandas: bool = False
         self.protocol_idx: int = 0
         self.stub_idx: int = 0
         self.type_var_idx: int = 0
@@ -38,6 +42,7 @@ class StubsGenerator:
     def generate_stubs(self) -> ast.Module:
         self.stubs = []
         self.typing_imports = set()
+        self.import_pandas = False
         for name, type in self.types._types.items():
             # Skip builtin types, not just based on name so the user can override
             # TODO: check if added members on builtin type
@@ -53,7 +58,7 @@ class StubsGenerator:
                     continue
             self.generate_stub(name, type)
 
-        imports = [
+        imports: list[ast.stmt] = [
             ast.ImportFrom(
                 module="__future__",
                 names=[ast.alias(name="annotations")],
@@ -70,6 +75,17 @@ class StubsGenerator:
                     level=0,
                 )
             )
+        if self.import_pandas:
+            imports.append(
+                ast.Import(
+                    names=[
+                        ast.alias(
+                            name="pandas",
+                            asname="pd",
+                        )
+                    ],
+                )
+            )
         return ast.Module(body=imports + self.stubs, type_ignores=[])
 
     def generate_stub(self, name: str, type: Type):
@@ -231,6 +247,31 @@ class StubsGenerator:
             case ConstraintType():
                 return self.dump_type(type.type)
 
+            case TupleType(items=items):
+                return ast.Subscript(
+                    value=ast.Name(id="tuple"),
+                    slice=ast.Tuple(
+                        elts=[self.dump_type(item) for item in items],
+                    ),
+                )
+
+            case ColumnType(type=inner):
+                self.import_pandas = True
+                return ast.Subscript(
+                    value=ast.Attribute(
+                        value=ast.Name(id="pd"),
+                        attr="Series",
+                    ),
+                    slice=self.dump_type(inner),
+                )
+
+            case DataFrameType():
+                self.import_pandas = True
+                return ast.Attribute(
+                    value=ast.Name(id="pd"),
+                    attr="DataFrame",
+                )
+
             case _:
                 assert_never(type)
 

midas/parser/midas.py

@@ -9,6 +9,7 @@ from midas.ast.midas import (
     Expr,
     ExtendStmt,
     ExtensionType,
+    FrameType,
     FunctionType,
     GenericType,
     GetExpr,
@@ -204,8 +205,10 @@ class MidasParser(Parser):
         return self.generic_type()
 
     def generic_type(self) -> Type:
-        type: Type = self.named_type()
+        type: NamedType = self.named_type()
         if self.check(TokenType.LEFT_BRACKET):
+            if type.name.lexeme == "Frame":
+                return self.frame_type()
             args: list[Type] = self.type_args()
             return GenericType(
                 location=Location.span(type.location, self.previous().get_location()),
@@ -224,7 +227,7 @@ class MidasParser(Parser):
         self.consume(TokenType.RIGHT_BRACKET, "Missing ']' after generic arguments")
         return args
 
-    def named_type(self) -> Type:
+    def named_type(self) -> NamedType:
         name: Token = self.consume_identifier("Expected type name")
         return NamedType(
             location=name.get_location(),
@@ -259,6 +262,32 @@ class MidasParser(Parser):
             members=members,
         )
 
+    def frame_type(self) -> FrameType:
+        keyword: Token = self.previous()
+        self.consume(TokenType.LEFT_BRACKET, "Expected '[' to start frame schema")
+
+        columns: list[FrameType.Column] = []
+        while not self.check(TokenType.RIGHT_BRACKET) and not self.is_at_end():
+            name: Token = self.advance()
+            self.consume(TokenType.COLON, "Expected ':' between column name and type")
+            type: Type = self.type_expr()
+            columns.append(
+                FrameType.Column(
+                    location=name.location_to(self.previous()),
+                    name=name,
+                    type=type,
+                )
+            )
+            if not self.match(TokenType.COMMA):
+                break
+
+        self.consume(TokenType.RIGHT_BRACKET, "Unclosed frame schema")
+
+        return FrameType(
+            location=keyword.location_to(self.previous()),
+            columns=columns,
+        )
+
     def constraint(self) -> Expr:
         """Parse a constraint
 

midas/typing.py

@@ -1,3 +1,4 @@
+from typing import Generic, TypeVar
 from typing import cast as typing_cast
 
 cast = typing_cast
@@ -32,3 +33,20 @@ This operation is unsound, use at your own risk!
 
 _**Internal Python documentation**_
 """
+
+
+T = TypeVar("T")
+
+
+class Frame(Generic[T]):
+    """A `Frame` is the abstract type implemented by `DataFrame`
+
+    A frame contains any number of named columns (see :class:`Column`)
+    """
+
+
+class Column(Generic[T]):
+    """A `Column` is the abstract type implemented by `Series`
+
+    A column contains a any number of values of the same type
+    """

tests/cases/checker/01_simple_types.py.ref.json

@@ -4,7 +4,35 @@
       "type": "Warning",
       "location": {
         "start": [
-          6,
+          8,
+          12
+        ],
+        "end": [
+          8,
+          43
+        ]
+      },
+      "message": "ConstraintType not yet supported"
+    },
+    {
+      "type": "Warning",
+      "location": {
+        "start": [
+          10,
+          10
+        ],
+        "end": [
+          10,
+          18
+        ]
+      },
+      "message": "Unknown type 'datetime'"
+    },
+    {
+      "type": "Warning",
+      "location": {
+        "start": [
+          13,
           4
         ],
         "end": [
@@ -12,7 +40,7 @@
           5
         ]
       },
-      "message": "FrameType not yet supported"
+      "message": "Unknown type '_'"
     }
   ],
   "judgments": []

tests/cases/checker/03_functions.py.ref.json

@@ -328,6 +328,19 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L6:9",
+        "to": "L6:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
     {
       "location": {
         "from": "L6:5",
@@ -373,19 +386,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L6:9",
-        "to": "L6:10"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
     {
       "location": {
         "from": "L6:5",
@@ -407,6 +407,32 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L7:9",
+        "to": "L7:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L7:12",
+        "to": "L7:15"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L7:5",
@@ -452,32 +478,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L7:9",
-        "to": "L7:10"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L7:12",
-        "to": "L7:15"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
     {
       "location": {
         "from": "L7:5",
@@ -503,6 +503,32 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L8:9",
+        "to": "L8:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L8:14",
+        "to": "L8:17"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L8:5",
@@ -548,32 +574,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L8:9",
-        "to": "L8:10"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L8:14",
-        "to": "L8:17"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
     {
       "location": {
         "from": "L8:5",
@@ -600,6 +600,45 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L9:9",
+        "to": "L9:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L9:12",
+        "to": "L9:15"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L9:17",
+        "to": "L9:23"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "test"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
     {
       "location": {
         "from": "L9:5",
@@ -645,45 +684,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L9:9",
-        "to": "L9:10"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L9:12",
-        "to": "L9:15"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
-    {
-      "location": {
-        "from": "L9:17",
-        "to": "L9:23"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "test"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
     {
       "location": {
         "from": "L9:5",
@@ -713,6 +713,45 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L10:9",
+        "to": "L10:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L10:12",
+        "to": "L10:15"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L10:19",
+        "to": "L10:22"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 3.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L10:5",
@@ -758,45 +797,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L10:9",
-        "to": "L10:10"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L10:12",
-        "to": "L10:15"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
-    {
-      "location": {
-        "from": "L10:19",
-        "to": "L10:22"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 3.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
     {
       "location": {
         "from": "L10:5",
@@ -827,6 +827,19 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L11:11",
+        "to": "L11:12"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
     {
       "location": {
         "from": "L11:5",
@@ -872,19 +885,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L11:11",
-        "to": "L11:12"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
     {
       "location": {
         "from": "L11:5",
@@ -906,6 +906,19 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L12:11",
+        "to": "L12:17"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "test"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
     {
       "location": {
         "from": "L12:5",
@@ -951,19 +964,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L12:11",
-        "to": "L12:17"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "test"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
     {
       "location": {
         "from": "L12:5",
@@ -985,6 +985,45 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L14:10",
+        "to": "L14:11"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L14:13",
+        "to": "L14:16"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L14:20",
+        "to": "L14:26"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "test"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
     {
       "location": {
         "from": "L14:6",
@@ -1030,45 +1069,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L14:10",
-        "to": "L14:11"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L14:13",
-        "to": "L14:16"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
-    {
-      "location": {
-        "from": "L14:20",
-        "to": "L14:26"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "test"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
     {
       "location": {
         "from": "L14:6",
@@ -1101,6 +1101,45 @@
         "name": "bool"
       }
     },
+    {
+      "location": {
+        "from": "L15:10",
+        "to": "L15:11"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L15:15",
+        "to": "L15:18"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L15:22",
+        "to": "L15:28"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "test"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
     {
       "location": {
         "from": "L15:6",
@@ -1146,45 +1185,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L15:10",
-        "to": "L15:11"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L15:15",
-        "to": "L15:18"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
-    {
-      "location": {
-        "from": "L15:22",
-        "to": "L15:28"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "test"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
     {
       "location": {
         "from": "L15:6",
@@ -1217,6 +1217,45 @@
         "name": "bool"
       }
     },
+    {
+      "location": {
+        "from": "L16:10",
+        "to": "L16:11"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L16:15",
+        "to": "L16:21"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "test"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
+    {
+      "location": {
+        "from": "L16:25",
+        "to": "L16:28"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2.0
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L16:6",
@@ -1262,45 +1301,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L16:10",
-        "to": "L16:11"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 1
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L16:15",
-        "to": "L16:21"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "test"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
-    {
-      "location": {
-        "from": "L16:25",
-        "to": "L16:28"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 2.0
-      },
-      "type": {
-        "name": "float"
-      }
-    },
     {
       "location": {
         "from": "L16:6",
@@ -1333,6 +1333,45 @@
         "name": "bool"
       }
     },
+    {
+      "location": {
+        "from": "L18:10",
+        "to": "L18:13"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "a"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
+    {
+      "location": {
+        "from": "L18:15",
+        "to": "L18:16"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 3
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L18:20",
+        "to": "L18:25"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": false
+      },
+      "type": {
+        "name": "bool"
+      }
+    },
     {
       "location": {
         "from": "L18:6",
@@ -1378,45 +1417,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L18:10",
-        "to": "L18:13"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": "a"
-      },
-      "type": {
-        "name": "str"
-      }
-    },
-    {
-      "location": {
-        "from": "L18:15",
-        "to": "L18:16"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": 3
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L18:20",
-        "to": "L18:25"
-      },
-      "expr": {
-        "_type": "LiteralExpr",
-        "value": false
-      },
-      "type": {
-        "name": "bool"
-      }
-    },
     {
       "location": {
         "from": "L18:6",

tests/cases/checker/06_subtyping.py.ref.json

@@ -100,6 +100,32 @@
         "name": "float"
       }
     },
+    {
+      "location": {
+        "from": "L11:13",
+        "to": "L11:15"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v1"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L11:17",
+        "to": "L11:19"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v2"
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L11:5",
@@ -135,32 +161,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L11:13",
-        "to": "L11:15"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "v1"
-      },
-      "type": {
-        "name": "int"
-      }
-    },
-    {
-      "location": {
-        "from": "L11:17",
-        "to": "L11:19"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "v2"
-      },
-      "type": {
-        "name": "float"
-      }
-    },
     {
       "location": {
         "from": "L11:5",

tests/cases/checker/07_variance.py.ref.json

@@ -72,29 +72,6 @@
     }
   ],
   "judgments": [
-    {
-      "location": {
-        "from": "L26:0",
-        "to": "L26:5"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "print"
-      },
-      "type": {
-        "pos_args": [
-          {
-            "pos": 0,
-            "name": "object",
-            "type": {},
-            "required": true
-          }
-        ],
-        "args": [],
-        "kw_args": [],
-        "returns": {}
-      }
-    },
     {
       "location": {
         "from": "L27:4",
@@ -325,6 +302,29 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L26:0",
+        "to": "L26:5"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "print"
+      },
+      "type": {
+        "pos_args": [
+          {
+            "pos": 0,
+            "name": "object",
+            "type": {},
+            "required": true
+          }
+        ],
+        "args": [],
+        "kw_args": [],
+        "returns": {}
+      }
+    },
     {
       "location": {
         "from": "L26:0",

tests/cases/checker/08_unification.py.ref.json

@@ -63,31 +63,6 @@
         "name": "float"
       }
     },
-    {
-      "location": {
-        "from": "L6:11",
-        "to": "L6:15"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "bool"
-      },
-      "type": {
-        "pos_args": [
-          {
-            "pos": 0,
-            "name": "object",
-            "type": {},
-            "required": false
-          }
-        ],
-        "args": [],
-        "kw_args": [],
-        "returns": {
-          "name": "bool"
-        }
-      }
-    },
     {
       "location": {
         "from": "L6:16",
@@ -135,6 +110,31 @@
         "name": "int"
       }
     },
+    {
+      "location": {
+        "from": "L6:11",
+        "to": "L6:15"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "bool"
+      },
+      "type": {
+        "pos_args": [
+          {
+            "pos": 0,
+            "name": "object",
+            "type": {},
+            "required": false
+          }
+        ],
+        "args": [],
+        "kw_args": [],
+        "returns": {
+          "name": "bool"
+        }
+      }
+    },
     {
       "location": {
         "from": "L6:11",
@@ -367,6 +367,54 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L12:21",
+        "to": "L12:27"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "double"
+      },
+      "type": {
+        "pos_args": [],
+        "args": [
+          {
+            "pos": 0,
+            "name": "value",
+            "type": {
+              "name": "float"
+            },
+            "required": true
+          }
+        ],
+        "kw_args": [],
+        "returns": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L12:29",
+        "to": "L12:35"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "floats"
+      },
+      "type": {
+        "name": "list",
+        "args": [
+          {
+            "name": "float"
+          }
+        ],
+        "body": {
+          "name": "list"
+        }
+      }
+    },
     {
       "location": {
         "from": "L12:17",
@@ -455,54 +503,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L12:21",
-        "to": "L12:27"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "double"
-      },
-      "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
-        "returns": {
-          "name": "float"
-        }
-      }
-    },
-    {
-      "location": {
-        "from": "L12:29",
-        "to": "L12:35"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "floats"
-      },
-      "type": {
-        "name": "list",
-        "args": [
-          {
-            "name": "float"
-          }
-        ],
-        "body": {
-          "name": "list"
-        }
-      }
-    },
     {
       "location": {
         "from": "L12:17",
@@ -538,6 +538,54 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L13:19",
+        "to": "L13:25"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "double"
+      },
+      "type": {
+        "pos_args": [],
+        "args": [
+          {
+            "pos": 0,
+            "name": "value",
+            "type": {
+              "name": "float"
+            },
+            "required": true
+          }
+        ],
+        "kw_args": [],
+        "returns": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L13:27",
+        "to": "L13:31"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "ints"
+      },
+      "type": {
+        "name": "list",
+        "args": [
+          {
+            "name": "int"
+          }
+        ],
+        "body": {
+          "name": "list"
+        }
+      }
+    },
     {
       "location": {
         "from": "L13:15",
@@ -626,54 +674,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L13:19",
-        "to": "L13:25"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "double"
-      },
-      "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
-        "returns": {
-          "name": "float"
-        }
-      }
-    },
-    {
-      "location": {
-        "from": "L13:27",
-        "to": "L13:31"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "ints"
-      },
-      "type": {
-        "name": "list",
-        "args": [
-          {
-            "name": "int"
-          }
-        ],
-        "body": {
-          "name": "list"
-        }
-      }
-    },
     {
       "location": {
         "from": "L13:15",
@@ -699,6 +699,54 @@
       },
       "type": {}
     },
+    {
+      "location": {
+        "from": "L14:15",
+        "to": "L14:21"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "is_odd"
+      },
+      "type": {
+        "pos_args": [],
+        "args": [
+          {
+            "pos": 0,
+            "name": "value",
+            "type": {
+              "name": "int"
+            },
+            "required": true
+          }
+        ],
+        "kw_args": [],
+        "returns": {
+          "name": "bool"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L14:23",
+        "to": "L14:27"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "ints"
+      },
+      "type": {
+        "name": "list",
+        "args": [
+          {
+            "name": "int"
+          }
+        ],
+        "body": {
+          "name": "list"
+        }
+      }
+    },
     {
       "location": {
         "from": "L14:11",
@@ -787,54 +835,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L14:15",
-        "to": "L14:21"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "is_odd"
-      },
-      "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "int"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
-        "returns": {
-          "name": "bool"
-        }
-      }
-    },
-    {
-      "location": {
-        "from": "L14:23",
-        "to": "L14:27"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "ints"
-      },
-      "type": {
-        "name": "list",
-        "args": [
-          {
-            "name": "int"
-          }
-        ],
-        "body": {
-          "name": "list"
-        }
-      }
-    },
     {
       "location": {
         "from": "L14:11",

tests/serializer/midas.py

@@ -8,6 +8,7 @@ from midas.ast.midas import (
     Expr,
     ExtendStmt,
     ExtensionType,
+    FrameType,
     FunctionType,
     GenericType,
     GetExpr,
@@ -197,3 +198,15 @@ class MidasAstJsonSerializer(
             "base": type.base.accept(self),
             "extension": type.extension.accept(self),
         }
+
+    def visit_frame_type(self, type: FrameType) -> dict:
+        return {
+            "_type": "FrameType",
+            "columns": [self._serialize_column(col) for col in type.columns],
+        }
+
+    def _serialize_column(self, column: FrameType.Column):
+        return {
+            "name": column.name.lexeme,
+            "type": column.type.accept(self),
+        }