if exprssion

toy-impl/parse_expr.py

@@ -38,6 +38,8 @@ def parse_expr(ctx: Context,
         return parse_call(ctx, sym_table, body)
     if isinstance(body, ast.Subscript):
         return parse_subscript(ctx, sym_table, body)
+    if isinstance(body, ast.IfExp):
+        return parse_if_expr(ctx, sym_table, body)
     raise CustomError(f'{body} is not yet supported')
 
 
@@ -65,10 +67,10 @@ def parse_constant(ctx: Context,
                    sym_table: dict[str, Type],
                    node):
     v = node.value
-    if isinstance(v, int):
+    if isinstance(v, bool):
-        return ctx.types['int32']
-    elif isinstance(v, bool):
         return ctx.types['bool']
+    elif isinstance(v, int):
+        return ctx.types['int32']
     else:
         raise CustomError(f'unknown constant {v}')
 
@@ -189,3 +191,16 @@ def parse_subscript(ctx: Context,
         else:
             raise CustomError(f'index of type {s} is not supported')
 
+def parse_if_expr(ctx: Context,
+                  sym_table: dict[str, Type],
+                  node):
+    b = ctx.types['bool']
+    t = parse_expr(ctx, sym_table, node.test)
+    if t != b:
+        raise CustomError(f'type of conditional must be bool instead of {t}')
+    ty1 = parse_expr(ctx, sym_table, node.body)
+    ty2 = parse_expr(ctx, sym_table, node.orelse)
+    if ty1 != ty2:
+        raise CustomError(f'divergent type for if expression: {ty1} != {ty2}')
+    return ty1
+

toy-impl/test_expr.py

@@ -76,6 +76,9 @@ test_expr('[1,2,3][:a:2]', {'a': I})
 test_expr('[1,2,3][:a:2]', {'a': i32})
 test_expr('a == a == a', {'a': I})
 test_expr('a == a and 1 == 2', {'a': I})
+test_expr('1 if a == b else 0', {'a': I, 'b': I})
+test_expr('a if a == b else 1', {'a': I, 'b': I})
+test_expr('a if a == b else b', {'a': I, 'b': I})
 
 test_classes = """
 class Foo: