feat(midas): generalize param spec of predicate and parse

gen/midas.py

@@ -58,9 +58,8 @@ class ExtendStmt:
 
 class PredicateStmt:
     name: Token
-    subject: Token
+    params: list[ParamSpec]
-    type: Type
+    body: Expr
-    condition: Expr
 
 
 ###<

midas/ast/midas.py

@@ -94,9 +94,8 @@ class ExtendStmt(Stmt):
 @dataclass(frozen=True)
 class PredicateStmt(Stmt):
     name: Token
-    subject: Token
+    params: list[ParamSpec]
-    type: Type
+    body: Expr
-    condition: Expr
 
     def accept(self, visitor: Stmt.Visitor[T]) -> T:
         return visitor.visit_predicate_stmt(self)

midas/ast/printer.py

@@ -150,13 +150,17 @@ class MidasAstPrinter(
         self._write_line("PredicateStmt")
         with self._child_level():
             self._write_line(f'name: "{stmt.name.lexeme}"')
-            self._write_line(f'subject: "{stmt.subject.lexeme}"')
+            self._write_line("params")
-            self._write_line("type")
+            with self._child_level():
+                for i, spec in enumerate(stmt.params):
+                    self._idx = i
+                    if i == len(stmt.params) - 1:
+                        self._mark_last()
+                    self._visit_param_spec(spec)
+
+            self._write_line("body", last=True)
             with self._child_level(single=True):
-                stmt.type.accept(self)
+                stmt.body.accept(self)
-            self._write_line("condition", last=True)
-            with self._child_level(single=True):
-                stmt.condition.accept(self)
 
     # Expressions
 
@@ -397,10 +401,9 @@ class MidasPrinter(m.Expr.Visitor[str], m.Stmt.Visitor[str], m.Type.Visitor[str]
 
     def visit_predicate_stmt(self, stmt: m.PredicateStmt):
         name: str = stmt.name.lexeme
-        subject: str = stmt.subject.lexeme
+        sig: str = "".join(self._visit_param_spec(spec) for spec in stmt.params)
-        type: str = stmt.type.accept(self)
+        body: str = stmt.body.accept(self)
-        condition: str = stmt.condition.accept(self)
+        return self.indented(f"predicate {name}{sig} = {body}")
-        return self.indented(f"predicate {name}({subject}: {type}) = {condition}")
 
     def visit_logical_expr(self, expr: m.LogicalExpr):
         left: str = expr.left.accept(self)

midas/checker/midas.py

@@ -13,6 +13,7 @@ from midas.checker.types import (
     ExtensionType,
     Function,
     GenericType,
+    Predicate,
     Type,
     TypeVar,
     UnknownType,
@@ -45,6 +46,8 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[Type
         builtins_path: Path = (Path(__file__).parent / "builtins.midas").resolve()
         self.process(builtins_path.read_text(), str(builtins_path))
 
+        self._bool: Type = self.get_type("bool")
+
     def process(self, source: str, path: Optional[str]):
         self.reporter = self.reporter.for_file(path)
         lexer: MidasLexer = MidasLexer(source)
@@ -114,7 +117,24 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[Type
             )
 
     def visit_predicate_stmt(self, stmt: m.PredicateStmt) -> None:
-        self.reporter.warning(stmt.location, "PredicateStmt not yet supported")
+        params: list[TypedParamSpec] = [
+            self._visit_param_spec(spec) for spec in stmt.params
+        ]
+        type: Type = self._bool
+        for spec in reversed(params):
+            type = Function(
+                pos_args=spec.pos,
+                args=spec.mixed,
+                kw_args=spec.kw,
+                returns=type,
+            )
+        self.types.define_predicate(
+            stmt.name.lexeme,
+            Predicate(
+                type=type,
+                body=stmt.body,
+            ),
+        )
 
     def visit_logical_expr(self, expr: m.LogicalExpr) -> None:
         self.reporter.warning(expr.location, "LogicalExpr not yet supported")

midas/checker/registry.py

@@ -11,6 +11,7 @@ from midas.checker.types import (
     Function,
     GenericType,
     OverloadedFunction,
+    Predicate,
     TopType,
     Type,
     TypeVar,
@@ -24,6 +25,7 @@ class TypesRegistry:
         self.logger: logging.Logger = logging.getLogger("TypesRegistry")
         self._types: dict[str, Type] = {}
         self._members: dict[str, dict[str, Type]] = {}
+        self._predicates: dict[str, Predicate] = {}
 
     def get_type(self, name: str) -> Type:
         """Get a type from its name
@@ -81,6 +83,11 @@ class TypesRegistry:
         else:
             members[member_name] = member_type
 
+    def define_predicate(self, name: str, predicate: Predicate):
+        if name in self._predicates:
+            raise ValueError(f"Predicate {name} already defined")
+        self._predicates[name] = predicate
+
     def is_subtype(self, type1: Type, type2: Type) -> bool:
         """Check whether `type1` is a subtype of `type2`
 

midas/checker/types.py

@@ -215,6 +215,12 @@ def unfold_type(type: Type) -> Type:
             return type
 
 
+@dataclass(frozen=True, kw_only=True)
+class Predicate:
+    type: Type
+    body: m.Expr
+
+
 Type = (
     TopType
     | BaseType

midas/parser/midas.py

@@ -506,20 +506,20 @@ class MidasParser(Parser):
             PredicateStmt: the parsed predicate declaration statement
         """
         keyword: Token = self.previous()
+
         name: Token = self.consume_identifier("Expected predicate name")
-        self.consume(TokenType.LEFT_PAREN, "Expected '(' before predicate subject")
+
-        subject: Token = self.consume_identifier("Expected subject name")
+        params: list[ParamSpec] = []
-        self.consume(TokenType.COLON, "Expected ':' after subject name")
+        while self.check(TokenType.LEFT_PAREN):
-        type: Type = self.type_expr()
+            params.append(self.function_args())
-        self.consume(TokenType.RIGHT_PAREN, "Expected ')' after predicate subject")
+
         self.consume(TokenType.EQUAL, "Expected '=' after predicate subject")
-        condition: Expr = self.constraint()
+        body: Expr = self.constraint()
         return PredicateStmt(
             location=keyword.location_to(self.previous()),
             name=name,
-            subject=subject,
+            params=params,
-            type=type,
+            body=body,
-            condition=condition,
         )
 
     def function(self) -> FunctionType:

tests/serializer/midas.py

@@ -80,9 +80,8 @@ class MidasAstJsonSerializer(
         return {
             "_type": "PredicateStmt",
             "name": stmt.name.lexeme,
-            "subject": stmt.subject.lexeme,
+            "params": [self._serialize_param_spec(spec) for spec in stmt.params],
-            "type": stmt.type.accept(self),
+            "body": stmt.body.accept(self),
-            "condition": stmt.condition.accept(self),
         }
 
     def visit_logical_expr(self, expr: LogicalExpr) -> dict: