Functional composition

When composing predicates for phantom types it won’t take long before you reach after functional composition. Unfortunately, fully supporting a typed n-ary compose functions isn’t yet feasible without shipping a custom mypy plugin. In lieu of having that effort in place, a simpler but fully typed compose2 function is shipped. The door, however, is left wide open for the possibility of shipping an n-ary, generalized compose function in the future.

phantom.fn.compose2(a, b)[source]

Returns a function composed from the two given functions a and b such that calling compose2(a, b)(x) is equivalent to calling a(b(x)).

>>> compose2("".join, reversed)("!olleH")
'Hello!'
Parameters
  • a (typing.Callable[[~AA], ~AR]) –

  • b (typing.Callable[[~BA], ~AA]) –

Return type

typing.Callable[[~BA], ~AR]