lib/trivial: add pipe function
#71348
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Profpatsch
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0.kind: enhancement
ofborg
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This LGTM, although personally I'd like a compose = flip pipe function.
I can understand the argument that it is confusing which order the functions will be applied, but there are a few places in our code-base at work I would like to use the compose function in a point-free manner.
`pipe` is a useful operator for creating pipelines of functions. It works around the usual problem of e.g. string operations becoming deeply nested functions. In principle, there are four different ways this function could be written: pipe val [ f1 .. fn ] pipe val [ fn .. f1 ] compose [ f1 .. fn ] val compose [ fn .. f1 ] val The third and fourth form mirror composition of functions, they would be the same as e.g. `(f1 << f2 << f3 .. << fn) val`. However, it is not clear which direction the list should have (as one can see in the second form, which is the most absurd. In order not to confuse users, we decide for the most “intuitive” form, which mirrors the way unix pipes work (thus the name `pipe`). The flow of data goes from left to right. Co-Authored-By: Silvan Mosberger <infinisil@icloud.com>
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I’m gonna keep this open till Sunday, to see if people have more feedback. |
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I've never really felt much need for such a function. Regular function composition seems fine to me, especially if one forgoes the dogma of indenting after parens 😉 For example pipe [ 3 4 ] [
(map toString)
(map (s: s + "\n"))
concatStrings
]vs. concatStrings
(map (s: s + "\n")
(map toString
([ 3 4 ])))or concatStrings
(map (s: s + "\n")
(map toString [ 3 4 ]))Where I concede that the ending run of parens is a bit of a nuisance. An example from Home Manager: https://github.com/rycee/home-manager/blob/024d1aa227978fe2dae2fb3e56bab9a7237c2401/modules/programs/firefox.nix#L212-L216 |
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Yeah I have to say, putting functions in lists which then get composed together somehow doesn't feel very intuitive. Composing functions manually much more so. |
Not just that, you cannot just reorder elements without re-shuffling the parens, or insert new ones without keeping track of the closing parens. Plus, as you say, that all will go away anyway once nix gains a good pretty-printer. |
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Since there’s been lots of positive feedback, let’s merge. |
pipeis a useful operator for creating pipelines of functions.It works around the usual problem of e.g. string operations becoming
deeply nested functions.
In principle, there are four different ways this function could be
written:
pipe val [ f1 .. fn ]
pipe val [ fn .. f1 ]
compose [ f1 .. fn ] val
compose [ fn .. f1 ] val
The third and fourth form mirror composition of functions, they would
be the same as e.g.
(f1 << f2 << f3 .. << fn) val.However, it is not clear which direction the list should have (as one
can see in the second form, which is the most absurd.
In order not to confuse users, we decide for the most “intuitive”
form, which mirrors the way unix pipes work (thus the name
pipe).The flow of data goes from left to right.
Co-Authored-By: Silvan Mosberger infinisil@icloud.com
Motivation for this change