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main.py

# remove the typing hints and mypy fails
from typing import Callable, Union

def fun1(x: int) -> Callable[[int], int]:
    return lambda y: x + y
    
x = fun1(1)

reveal_type(x)
    
def funf(f: Callable[[int], int]) -> int:
    return f(1)
    
y = funf(lambda x: x)
reveal_type(y)

def funz(x):
    return x
    
z: int = funz(3)
reveal_type(z)

def funk(x):
    return lambda y: y

# a = funk(1)
a: Callable[..., int] = funk(1)(1)
reveal_type(a)

# (𝜆𝑓 . 𝑓 1) : ((𝐼 → 𝐼 ) & (𝐹 → 𝐹 )) → 𝐼 
def funsubs(f) -> Union[Callable[[int], int], Callable[[float], float]]:
    return f(1)
    
b = funsubs(lambda x: x)
# reveals union or float
reveal_type(b(1))

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