Nix: Add an infix reverse-application operator

[pacien]

I couldn't find this handy pipe-like operator:

val (|>) : 'a -> ('a -> 'b) -> 'b
Reverse-application operator: x |> f |> g is exactly equivalent to g (f (x)).

Example use case:
builtins.readDir "/dir" |> builtins.attrNames
instead of
buitins.attrNames (builtins.readDir "/dir")

[copumpkin]

The extensive haskell subcommunity in Nix will probably want $ too, if this goes in 😄

[regnat]

@copumpkin you mean https://github.com/NixOS/nix/issues/1845 ? :smile:

[copumpkin]

And before you know it, Nix will support Agda-style arbitrary mixfix operators 😄

[danbst]

nix-repl> let __div = x: y: y x; in
          builtins.readDir "/etc" / builtins.attrNames / builtins.length
77
nix-repl> let __mul = x: y: if builtins.typeOf y != "lambda" then x y else z: x (y z); in 
          builtins.length * builtins.attrNames * builtins.readDir "/etc"
77

ans so on (https://github.com/NixOS/nix/issues/861)

[alexameen]

Yes please!

[Ninlives]

Any progress?

[edolstra]

No, there are no plans to add this.