diff --git a/midas/checker/builtins.py b/midas/checker/builtins.py
index daf0015..78ba18f 100644
--- a/midas/checker/builtins.py
+++ b/midas/checker/builtins.py
@@ -15,7 +15,7 @@ if TYPE_CHECKING:
 
 
 BUILTIN_SUBTYPES: dict[str, set[str]] = {
-    "object": {"float", "list", "dict"},
+    "object": {"float", "list", "dict", "str"},
     "float": {"int"},
     "int": {"bool"},
 }
diff --git a/midas/checker/diagnostic.py b/midas/checker/diagnostic.py
index f4b3d12..233dd74 100644
--- a/midas/checker/diagnostic.py
+++ b/midas/checker/diagnostic.py
@@ -9,6 +9,7 @@ class DiagnosticType(StrEnum):
     ERROR = "Error"
     WARNING = "Warning"
     INFO = "Info"
+    DEBUG = "Debug"
 
 
 @dataclass(frozen=True)
diff --git a/midas/checker/evaluator.py b/midas/checker/evaluator.py
new file mode 100644
index 0000000..c21f1c2
--- /dev/null
+++ b/midas/checker/evaluator.py
@@ -0,0 +1,172 @@
+from dataclasses import dataclass
+from typing import Any, Callable, Optional
+
+import midas.ast.midas as m
+from midas.checker.preamble import Preamble
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import Function, Predicate
+from midas.lexer.token import TokenType
+
+
+@dataclass(frozen=True, kw_only=True)
+class PartialPredicate(Predicate):
+    scope: dict[str, Any]
+
+
+class Evaluator(m.Expr.Visitor[Any]):
+    def __init__(self, types: TypesRegistry, reporter: Optional[FileReporter] = None):
+        self.types: TypesRegistry = types
+        self.reporter: Optional[FileReporter] = reporter
+        self.preamble: Preamble = Preamble(self.types)
+        self.scopes: list[dict[str, Any]] = [{}]
+
+    def evaluate(self, expr: m.Expr) -> Any:
+        value: Any = expr.accept(self)
+        if self.reporter is not None:
+            self.reporter.debug(expr.location, f"Value: {value}")
+        return value
+
+    def get_value(self, name: str) -> Any:
+        scope: dict[str, Any] = self.scopes[-1]
+        return scope[name]
+
+    def set_value(self, name: str, value: Any, force_declare: bool = False):
+        if not force_declare:
+            for scope in reversed(self.scopes):
+                if name in scope:
+                    scope[name] = value
+                    return
+        self.scopes[-1][name] = value
+
+    def visit_logical_expr(self, expr: m.LogicalExpr) -> Any:
+        def left():
+            return self.evaluate(expr.left)
+
+        def right():
+            return self.evaluate(expr.right)
+
+        match expr.operator.type:
+            case TokenType.AND:
+                return left() and right()
+            case _:
+                raise NotImplementedError
+
+    def visit_binary_expr(self, expr: m.BinaryExpr) -> Any:
+        left: Any = self.evaluate(expr.left)
+        right: Any = self.evaluate(expr.right)
+        match expr.operator.type:
+            case TokenType.MINUS:
+                return left - right
+            case TokenType.STAR:
+                return left * right
+            case TokenType.SLASH:
+                return left / right
+            case TokenType.GREATER:
+                return left > right
+            case TokenType.GREATER_EQUAL:
+                return left >= right
+            case TokenType.LESS:
+                return left < right
+            case TokenType.LESS_EQUAL:
+                return left <= right
+            case TokenType.EQUAL_EQUAL:
+                return left == right
+            case TokenType.BANG_EQUAL:
+                return left != right
+            case _:
+                raise NotImplementedError
+
+    def visit_unary_expr(self, expr: m.UnaryExpr) -> Any:
+        right: Any = self.evaluate(expr.right)
+        match expr.operator.type:
+            case TokenType.MINUS:
+                return -right
+            case _:
+                raise NotImplementedError
+
+    def visit_call_expr(self, expr: m.CallExpr) -> Any:
+        callee: Any = self.evaluate(expr.callee)
+        args: list[Any] = [self.evaluate(arg) for arg in expr.arguments]
+        kwargs: dict[str, Any] = {
+            name: self.evaluate(arg) for name, arg in expr.keywords.items()
+        }
+
+        match callee:
+            case Predicate():
+                return self._evaluate_predicate(callee, args, kwargs)
+            case _ if callable(callee):
+                return callee(*args, **kwargs)
+            case _:
+                return NotImplementedError
+
+    def visit_get_expr(self, expr: m.GetExpr) -> Any:
+        obj: Any = self.evaluate(expr.expr)
+        return getattr(obj, expr.name.lexeme)
+
+    def visit_variable_expr(self, expr: m.VariableExpr) -> Any:
+        name: str = expr.name.lexeme
+        for scope in reversed(self.scopes):
+            if name in scope:
+                return scope[name]
+
+        predicate: Optional[Predicate] = self.types.lookup_predicate(name)
+        if predicate is not None:
+            if predicate.alias:
+                return self.evaluate(predicate.body)
+            return predicate
+
+        glob: Optional[Callable] = self.preamble.get_py_func(name)
+        if glob is not None:
+            return glob
+        raise NameError(f"Unknown variable '{name}'")
+
+    def visit_grouping_expr(self, expr: m.GroupingExpr) -> Any:
+        return self.evaluate(expr.expr)
+
+    def visit_literal_expr(self, expr: m.LiteralExpr) -> Any:
+        return expr.value
+
+    def visit_wildcard_expr(self, expr: m.WildcardExpr) -> Any:
+        return self.get_value("_")
+
+    def _evaluate_predicate(
+        self, predicate: Predicate, args: list[Any], kwargs: dict[str, Any]
+    ) -> Any:
+        res: Any = None
+        if isinstance(predicate, PartialPredicate):
+            self.scopes.append(predicate.scope)
+        else:
+            self.scopes.append({})
+        match predicate.type:
+            case Function(returns=Function() as inner):
+                self._map_args(predicate.type, args, kwargs)
+                res = PartialPredicate(
+                    type=inner,
+                    body=predicate.body,
+                    alias=False,
+                    scope=self.scopes[-1],
+                )
+
+            case Function():
+                self._map_args(predicate.type, args, kwargs)
+                res = self.evaluate(predicate.body)
+
+            case _:
+                raise NotImplementedError
+        self.scopes.pop()
+        return res
+
+    def _map_args(self, function: Function, args: list[Any], kwargs: dict[str, Any]):
+        positional: list[Function.Argument] = function.pos_args + function.args
+        keywords: dict[str, Function.Argument] = {
+            arg.name: arg for arg in function.args + function.kw_args
+        }
+
+        for i, arg in enumerate(args):
+            param: Function.Argument = positional[i]
+            self.set_value(param.name, arg)
+
+        for name, arg in kwargs.items():
+            param: Function.Argument = keywords[name]
+            self.set_value(param.name, arg)
diff --git a/midas/checker/preamble.py b/midas/checker/preamble.py
index 1dcd157..feea8b7 100644
--- a/midas/checker/preamble.py
+++ b/midas/checker/preamble.py
@@ -1,4 +1,5 @@
 from dataclasses import dataclass
+from typing import Callable, Optional
 
 from midas.checker.environment import Environment
 from midas.checker.registry import TypesRegistry
@@ -16,16 +17,18 @@ class Preamble(Environment):
     def __init__(self, types: TypesRegistry) -> None:
         super().__init__()
         self._types: TypesRegistry = types
+        self._python_funcs: dict[str, Callable] = {}
 
-        self._def_type_constructor("object")
-        self._def_type_constructor("float")
-        self._def_type_constructor("int")
-        self._def_type_constructor("bool")
-        self._def_type_constructor("str")
+        self._def_type_constructor("object", object)
+        self._def_type_constructor("float", float)
+        self._def_type_constructor("int", int)
+        self._def_type_constructor("bool", bool)
+        self._def_type_constructor("str", str)
         self._def_function(
             name="list",
             pos=[Param("object", TopType())],
             returns=self._list_of(TopType()),
+            py_function=list,
         )
 
         # TODO: use sink
@@ -33,6 +36,7 @@ class Preamble(Environment):
             name="print",
             pos=[Param("object", TopType())],
             returns=UnitType(),
+            py_function=print,
         )
 
         map_in = TypeVar(name="T", bound=None)
@@ -53,6 +57,7 @@ class Preamble(Environment):
             ],
             returns=self._list_of(map_out),  # TODO: replace with Iterable[U]
             type_vars=[map_in, map_out],
+            py_function=map,
         )
         self._def_function(
             name="input",
@@ -63,12 +68,13 @@ class Preamble(Environment):
     def _list_of(self, item_type: Type) -> Type:
         return self._types.apply_generic(self._types.get_type("list"), [item_type])
 
-    def _def_type_constructor(self, name: str):
+    def _def_type_constructor(self, name: str, py_function: Optional[Callable] = None):
         # TODO: more specific arg types
         self._def_function(
             name=name,
             pos=[Param("object", TopType(), required=False)],
             returns=self._types.get_type(name),
+            py_function=py_function,
         )
 
     def _make_function(
@@ -115,6 +121,7 @@ class Preamble(Environment):
         kw: list[Param] = [],
         returns: Type = UnitType(),
         type_vars: list[TypeVar] = [],
+        py_function: Optional[Callable] = None,
     ):
         function: Type = self._make_function(
             name=name,
@@ -125,3 +132,8 @@ class Preamble(Environment):
             type_vars=type_vars,
         )
         self.define(name, function)
+        if py_function is not None:
+            self._python_funcs[name] = py_function
+
+    def get_py_func(self, name: str) -> Optional[Callable]:
+        return self._python_funcs.get(name)
diff --git a/midas/checker/python.py b/midas/checker/python.py
index 435f6f1..ffa1600 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -1,11 +1,13 @@
 import ast
 import logging
 from dataclasses import dataclass
-from typing import Optional
+from typing import Any, Optional
 
 import midas.ast.python as p
 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.operators import (
     PY_COMPARATOR_METHODS,
     PY_OPERATOR_METHODS,
@@ -18,6 +20,8 @@ from midas.checker.resolver import Resolver
 from midas.checker.types import (
     AliasType,
     AppliedType,
+    BaseType,
+    ConstraintType,
     Function,
     GenericType,
     OverloadedFunction,
@@ -71,6 +75,7 @@ class PythonTyper(
         self.env: Environment = self.global_env
         self.locals: dict[p.Expr, int] = {}
         self.judgements: list[tuple[p.Expr, Type]] = []
+        self.evaluated_casts: list[p.CastExpr] = []
 
     def process(self, source: str, path: Optional[str]) -> TypedAST:
         self.reporter = self.reporter.for_file(path)
@@ -84,10 +89,15 @@ class PythonTyper(
         self.env = self.global_env
         self.locals = resolver.locals
         self.judgements = []
+        self.evaluated_casts = []
 
         self.check(stmts)
 
-        return TypedAST(stmts=stmts, judgements=self.judgements)
+        return TypedAST(
+            stmts=stmts,
+            judgements=self.judgements,
+            evaluated_casts=self.evaluated_casts,
+        )
 
     def judge(self, expr: p.Expr, type: Type):
         """Record a typing judgement
@@ -538,8 +548,16 @@ class PythonTyper(
         return UnknownType()
 
     def visit_cast_expr(self, expr: p.CastExpr) -> Type:
-        _ = self.type_of(expr.expr)
-        return self.resolve_type_expr(expr.type)
+        subject_type: Type = self.type_of(expr.expr)
+        target_type: Type = self.resolve_type_expr(expr.type)
+        is_lit, lit_value = self._get_literal(expr.expr)
+        if is_lit:
+            evaluated: bool = self._evaluate_cast_statically(
+                expr, subject_type, target_type, lit_value
+            )
+            if evaluated:
+                self.evaluated_casts.append(expr)
+        return target_type
 
     def visit_ternary_expr(self, expr: p.TernaryExpr) -> Type:
         test_type: Type = self.type_of(expr.test)
@@ -1108,3 +1126,93 @@ class PythonTyper(
                 return p.BaseType(location=location, base=name, param=None)
             case _:
                 raise NotImplementedError
+
+    def _get_literal(self, expr: p.Expr) -> tuple[bool, Any]:
+        match expr:
+            case p.LiteralExpr(value=value):
+                return True, value
+
+            case p.ListExpr(items=items):
+                values: list[Any] = []
+                for item in items:
+                    is_lit, value = self._get_literal(item)
+                    if not is_lit:
+                        return False, None
+                    values.append(value)
+                return True, values
+
+            case p.DictExpr(keys=keys, values=values):
+                pairs: list[tuple[Any, Any]] = []
+                for key, value in zip(keys, values):
+                    key_val = None
+                    if key is not None:
+                        is_lit, key_val = self._get_literal(key)
+                        if not is_lit:
+                            return False, None
+
+                    is_lit, value_val = self._get_literal(value)
+                    if not is_lit:
+                        return False, None
+
+                    if key is None:
+                        # TODO: check that value is always a dict
+                        assert isinstance(value_val, dict)
+                        pairs.extend(value_val.items())
+                    else:
+                        pairs.append((key_val, value_val))
+                return True, dict(pairs)
+
+            case _:
+                return False, None
+
+    def _evaluate_cast_statically(
+        self, expr: p.CastExpr, subject_type: Type, target_type: Type, lit_value: Any
+    ) -> bool:
+        match target_type:
+            case AliasType(type=base):
+                return self._evaluate_cast_statically(
+                    expr, subject_type, base, lit_value
+                )
+
+            case AppliedType(body=body):
+                return self._evaluate_cast_statically(
+                    expr, subject_type, body, lit_value
+                )
+
+            case ConstraintType(type=base, constraint=constraint):
+                evaluated: bool = True
+                if not self._evaluate_cast_statically(
+                    expr, subject_type, base, lit_value
+                ):
+                    evaluated = False
+
+                evaluator = Evaluator(self.types)
+                evaluator.set_value("_", lit_value)
+                res = evaluator.evaluate(constraint)
+                if not res:
+                    printer = MidasPrinter()
+                    constraint_str: str = printer.print(constraint)
+                    self.reporter.error(
+                        expr.location,
+                        f"Value {lit_value!r} does not fit constraint '{constraint_str}'",
+                    )
+                    evaluated = False
+                return evaluated
+
+            case BaseType():
+                # TODO: do we want to allow cast(float, int)? would require runtime conversion
+                if not self.types.is_subtype(
+                    subject_type, target_type
+                ) or not self.types.is_subtype(target_type, subject_type):
+                    self.reporter.error(
+                        expr.location,
+                        f"Value {lit_value!r} of type {subject_type} cannot be cast as {target_type}",
+                    )
+                    return False
+                return True
+
+            case _:
+                self.reporter.info(
+                    expr.location, f"Cannot evaluate cast to {target_type} statically"
+                )
+                return False
diff --git a/midas/checker/reporter.py b/midas/checker/reporter.py
index b68766a..b61b8f3 100644
--- a/midas/checker/reporter.py
+++ b/midas/checker/reporter.py
@@ -61,3 +61,10 @@ class FileReporter:
             location=location,
             message=message,
         )
+
+    def debug(self, location: Location, message: str):
+        self.report(
+            type=DiagnosticType.DEBUG,
+            location=location,
+            message=message,
+        )
diff --git a/midas/cli/utils.py b/midas/cli/utils.py
index 793d4e1..6cc7d38 100644
--- a/midas/cli/utils.py
+++ b/midas/cli/utils.py
@@ -59,6 +59,7 @@ class DiagnosticPrinter:
             DiagnosticType.ERROR: Ansi.RED,
             DiagnosticType.WARNING: Ansi.YELLOW,
             DiagnosticType.INFO: Ansi.CYAN,
+            DiagnosticType.DEBUG: Ansi.MAGENTA,
         }.get(diagnostic.type, Ansi.WHITE)
 
         subject: str = Ansi.FG(color) + line[start_offset:end_offset] + Ansi.RESET
diff --git a/midas/generator/generator.py b/midas/generator/generator.py
index e66f532..0fba91e 100644
--- a/midas/generator/generator.py
+++ b/midas/generator/generator.py
@@ -44,6 +44,7 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
         self._typed_ast: TypedAST = TypedAST(
             stmts=[],
             judgements=[],
+            evaluated_casts=[],
         )
         self._alias_count: int = 0
         self._predicate_count: int = 0
@@ -131,6 +132,10 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
 
     def visit_cast_expr(self, expr: p.CastExpr) -> ast.expr:
         expr2: ast.expr = expr.expr.accept(self)
+
+        if expr in self._typed_ast.evaluated_casts:
+            return expr2
+
         alias: ast.expr = self._make_alias(expr2)
 
         type: Type = self._get_expr_type(expr)
diff --git a/midas/utils.py b/midas/utils.py
index f10bdb3..0ac90cf 100644
--- a/midas/utils.py
+++ b/midas/utils.py
@@ -62,3 +62,4 @@ class UniversalJSONDumper:
 class TypedAST:
     stmts: list[p.Stmt]
     judgements: list[tuple[p.Expr, Type]]
+    evaluated_casts: list[p.CastExpr]
diff --git a/tests/cases/checker/04_custom_types.py.ref.json b/tests/cases/checker/04_custom_types.py.ref.json
index 1802082..d502a97 100644
--- a/tests/cases/checker/04_custom_types.py.ref.json
+++ b/tests/cases/checker/04_custom_types.py.ref.json
@@ -1,6 +1,19 @@
 {
   "diagnostics": [],
   "judgments": [
+    {
+      "location": {
+        "from": "L4:30",
+        "to": "L4:36"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 123.45
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L4:18",
@@ -25,6 +38,19 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L5:28",
+        "to": "L5:31"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 6.7
+      },
+      "type": {
+        "name": "float"
+      }
+    },
     {
       "location": {
         "from": "L5:15",
diff --git a/tests/cases/generator/01_simple_types.py.ref.txt b/tests/cases/generator/01_simple_types.py.ref.txt
index f8da6a6..f434968 100644
--- a/tests/cases/generator/01_simple_types.py.ref.txt
+++ b/tests/cases/generator/01_simple_types.py.ref.txt
@@ -7,68 +7,14 @@ Module(
         alias(name='Meter'),
         alias(name='Second')],
       level=0),
-    Assign(
-      targets=[
-        Name(id='__midas_a0__')],
-      value=Constant(value=123.45)),
-    Assert(
-      test=Call(
-        func=Name(id='isinstance'),
-        args=[
-          Name(id='__midas_a0__'),
-          Name(id='float')],
-        keywords=[]),
-      msg=JoinedStr(
-        values=[
-          Constant(value='01_simple_types.py:L3:19: CastError: Cannot cast '),
-          FormattedValue(
-            value=Attribute(
-              value=Call(
-                func=Name(id='type'),
-                args=[
-                  Name(id='__midas_a0__')],
-                keywords=[]),
-              attr='__name__'),
-            conversion=-1),
-          Constant(value=' to float')])),
     Assign(
       targets=[
         Name(id='distance')],
-      value=Name(id='__midas_a0__')),
-    Delete(
-      targets=[
-        Name(id='__midas_a0__')]),
-    Assign(
-      targets=[
-        Name(id='__midas_a1__')],
-      value=Constant(value=6.7)),
-    Assert(
-      test=Call(
-        func=Name(id='isinstance'),
-        args=[
-          Name(id='__midas_a1__'),
-          Name(id='float')],
-        keywords=[]),
-      msg=JoinedStr(
-        values=[
-          Constant(value='01_simple_types.py:L4:16: CastError: Cannot cast '),
-          FormattedValue(
-            value=Attribute(
-              value=Call(
-                func=Name(id='type'),
-                args=[
-                  Name(id='__midas_a1__')],
-                keywords=[]),
-              attr='__name__'),
-            conversion=-1),
-          Constant(value=' to float')])),
+      value=Constant(value=123.45)),
     Assign(
       targets=[
         Name(id='time')],
-      value=Name(id='__midas_a1__')),
-    Delete(
-      targets=[
-        Name(id='__midas_a1__')]),
+      value=Constant(value=6.7)),
     Assign(
       targets=[
         Name(id='speed')],