feat(checker): handle ternary expression

examples/01_simple_type_checking/03_control_flow.py

@@ -12,3 +12,5 @@ def factorial(n: int) -> int:
     if n <= 1:
         return 1
     return n * factorial(n - 1)
+
+category = "Category 1" if a < 10 else "Category 2"

gen/python.py

@@ -139,4 +139,10 @@ class CastExpr:
     expr: Expr
 
 
+class TernaryExpr:
+    test: Expr
+    if_true: Expr
+    if_false: Expr
+
+
 ###<

midas/ast/printer.py

@@ -465,6 +465,7 @@ class PythonAstPrinter(
         self._write_line("IfStmt")
         with self._child_level():
             self._write_line("test")
+            with self._child_level(single=True):
                 stmt.test.accept(self)
             self._write_line("body")
             with self._child_level():
@@ -592,3 +593,18 @@ class PythonAstPrinter(
             self._write_line("expr", last=True)
             with self._child_level(single=True):
                 expr.expr.accept(self)
+
+    def visit_ternary_expr(self, expr: p.TernaryExpr) -> None:
+        self._write_line("TernaryExpr")
+        with self._child_level():
+            self._write_line("test")
+            with self._child_level(single=True):
+                expr.test.accept(self)
+            
+            self._write_line("if_true")
+            with self._child_level(single=True):
+                expr.if_true.accept(self)
+            
+            self._write_line("if_false", last=True)
+            with self._child_level(single=True):
+                expr.if_false.accept(self)

midas/ast/python.py

@@ -220,6 +220,9 @@ class Expr(ABC):
         @abstractmethod
         def visit_cast_expr(self, expr: CastExpr) -> T: ...
 
+        @abstractmethod
+        def visit_ternary_expr(self, expr: TernaryExpr) -> T: ...
+
 
 @dataclass(frozen=True)
 class BinaryExpr(Expr):
@@ -312,3 +315,13 @@ class CastExpr(Expr):
 
     def accept(self, visitor: Expr.Visitor[T]) -> T:
         return visitor.visit_cast_expr(self)
+
+
+@dataclass(frozen=True)
+class TernaryExpr(Expr):
+    test: Expr
+    if_true: Expr
+    if_false: Expr
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_ternary_expr(self)

midas/checker/checker.py

@@ -9,7 +9,7 @@ from midas.ast.location import Location
 from midas.checker.diagnostic import Diagnostic, DiagnosticType
 from midas.checker.environment import Environment
 from midas.checker.operators import COMPARATOR_METHODS, OPERATOR_METHODS
-from midas.checker.types import Function, Type, UnitType, UnknownType
+from midas.checker.types import BaseType, Function, SimpleType, Type, UnitType, UnknownType
 from midas.lexer.midas import MidasLexer
 from midas.lexer.token import Token
 from midas.parser.midas import MidasParser
@@ -405,6 +405,22 @@ class Checker(
     def visit_cast_expr(self, expr: p.CastExpr) -> Type:
         return expr.type.accept(self)
 
+    def visit_ternary_expr(self, expr: p.TernaryExpr) -> Type:
+        test_type: Type = expr.test.accept(self)
+
+        # TODO Allow subtypes or any type
+        if test_type != self.ctx.get_type("bool"):
+            self.error(
+                expr.test.location, f"If test must be a boolean, got {test_type}"
+            )
+
+        true_type: Type = expr.if_true.accept(self)
+        false_type: Type = expr.if_false.accept(self)
+        if true_type != false_type:
+            self.error(expr.location, f"Type mismatch in ternary if branches: true={true_type} != false={false_type}")
+            return UnknownType()
+        return true_type
+
     def visit_base_type(self, node: p.BaseType) -> Type:
         return self.ctx.get_type(node.base)
 

midas/cli/highlighter.py

@@ -203,6 +203,8 @@ class PythonHighlighter(
 
     def visit_cast_expr(self, expr: p.CastExpr) -> None: ...
 
+    def visit_ternary_expr(self, expr: p.TernaryExpr) -> None: ...
+
 
 class MidasHighlighter(Highlighter, m.Stmt.Visitor[None], m.Expr.Visitor[None]):
     EXTRA_CSS_PATH: Optional[Path] = Path(__file__).parent / "hl_midas.css"

midas/parser/python.py

@@ -22,6 +22,7 @@ from midas.ast.python import (
     MidasType,
     ReturnStmt,
     Stmt,
+    TernaryExpr,
     TypeAssign,
     UnaryExpr,
     VariableExpr,
@@ -389,6 +390,9 @@ class PythonParser:
             case ast.Call():
                 return self.parse_call(node)
 
+            case ast.IfExp():
+                return self.parse_ternary(node)
+
             case ast.Constant(value=value):
                 return LiteralExpr(location=location, value=value)
 
@@ -478,3 +482,11 @@ class PythonParser:
                 if arg.arg is not None  # Should always be True, type checker happy
             },
         )
+
+    def parse_ternary(self, node: ast.IfExp) -> TernaryExpr:
+        return TernaryExpr(
+            location=Location.from_ast(node),
+            test=self.parse_expr(node.test),
+            if_true=self.parse_expr(node.body),
+            if_false=self.parse_expr(node.orelse),
+        )

midas/resolver/resolver.py

@@ -180,3 +180,8 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
     def visit_cast_expr(self, expr: p.CastExpr) -> None:
         self.resolve(expr.expr)
+
+    def visit_ternary_expr(self, expr: p.TernaryExpr) -> None:
+        self.resolve(expr.test)
+        self.resolve(expr.if_true)
+        self.resolve(expr.if_false)