hildensia / matcher

A haskell like pattern matching for python 3.

matcher

A haskell like pattern matching for python 3.

Equality matching

You can match everything that defines a __eq__ function:

from matcher import Match


@Match
def func(a, b: 5):
    print("b is 5 here")
    

@Match
def func(a: 5, b):
    print("a is 5 here")
     

@Match
def func(a, b):
    print("a and b are not 5 here")

Expression matching

You can also match against expressions, that evaluate to a truthy value. In these expressions all parameters are set to their actual value at runtime. Unfortunately we have to put them in a string to evaluate them at call time. (You can also put any truthy expression there, that evaluates at definition time):

@Match
def multi_var_expr_func(a, b) -> 'a > b':
    print("a is bigger than b")


@Match
def multi_var_expr_func(a, b) -> 'a <= b':
    print("b is bigger than or equal to a")

Order of matching

The matches are evaluated in the order they appear in the file and the first match is called. So given the little program above the following would happend:

>>> func(5, 3)
a is 5 here

>>> func(5, 5)
b is 5 here

>>> func(1, 2)
a and b are not 5 here