foreach_i

I’d like to propose a new util: foreach_i.

Motivation

You know how JS’s Array.map also passes the element index as a 2nd parameter to the function?

> ['a', 'b', 'c'].map((x, i) => `Element ${i} is ${x}`)
[ 'Element 0 is a', 'Element 1 is b', 'Element 2 is c' ]

That’s exactly what I’m trying to do here. The only difference is that the index would be passed as the 1st param:

def test_foreach_i():
    
    r = ['a', 'b', 'c'] > (pipe
                          | foreach_i(lambda i, x: f'Element {i} is {x}')
                          | list
                          )
    
    assert r == [ 'Element 0 is a'
                , 'Element 1 is b'
                , 'Element 2 is c'    
                ]

(Naïve) Implementation

from pipetools.utils import foreach, as_args
from typing import Callable, TypeVar


A = TypeVar('A')
B = TypeVar('B')

def foreach_i(f: Callable[[int, A], B]):
    
    return enumerate | foreach(as_args(f))

The same could be done for foreach_do.

[0101]

I see. Technically, you can instead do:

tds = tr > enumerate | foreach((X[1], X[0] | colWidth.__getitem__))

But it’s quite unreadable.

---

I think what we could do is detect if a two-parameter function is being passed in and then pass two separate parameters - and otherwise pass in the tuple so things like foreach_i("Element {0} is {1}") still work as expected.

[tfga]

Not really.

Every once in a while I find myself in a situation where I want to do a “foreach with index”. The particular piece of code that prompted me to write this issue was:

# (i, td) => (td, colWidth[i])
def pairWithWidth(i, td): return td, colWidth[i]

tds = tr >  (pipe
            | enumerate
            | foreach(as_args(pairWithWidth))
            | foreach(as_args(addPadding))
            | ' '.join
            )

With foreach_i, it would become:

# (i, td) => (td, colWidth[i])
def pairWithWidth(i, td): return td, colWidth[i]

tds = tr >  (pipe
            | foreach_i(pairWithWidth)
            | foreach(as_args(addPadding))
            | ' '.join
            )