Adding an operator like Haskell's '$'

[Ekleog]

The title says it all, I'm thinking it would be useful for eg.

builtins.trace "my debug stuff" $
# some multiline complex code that would require parenthesing otherwise

What do you think about it? I guess it's too late for the feature freeze, but $ being already reserved for ${} I guess it wouldn't be a breaking change anyway.

[dtzWill]

This would be crazy useful for exactly the use case described here, I run into this often! 😁

[lheckemann]

Also for (import <nixpkgs> {}).callPackage $!

[Ekleog]

Also for builtins.seq.

[lilyball]

I really want this operator. And in particular, the right-hand side should support functions, because that's really what I want this for. I want to be able to take an existing

{ foo, bar }:
…

and change it to

lib.makeOverridable $
{ foo, bar }:
…

[lilyball]

Keywords to improve search discoverability of this issue: infix application operator

[lilyball]

On a similar note I'd also like the composition operator (.), though I find its lack less annoying than the lack of the application operator.

[stale]

I marked this as stale due to inactivity. → More info

[lheckemann]

We still want this!

[stale]

I marked this as stale due to inactivity. → More info

[lilyball]

I still want this very much!

[stale]

I marked this as stale due to inactivity. → More info

[infinisil]

I think $ is a hard sell, but here's an alternative that might get wider approval:

apply foo;
apply bar;
baz

# Equivalent to
foo (bar baz)

Advantages compared to $:

• It fits better into the Nix syntax, which already supports with ...; and assert ...;
• It mirrors both the syntax and semantics of the new experimental CLI's --apply option

Disadvantages:

• It requires a new keyword to be reserved, thus requiring something like [RFC 0137] Nix language versioning rfcs#137

[piegamesde]

FYI there is now an RFC that proposes something similar, people in here might have opinions about |> vs <| that I'd be interested in hearing.

NixOS/rfcs#148

[thufschmitt]

This is a change with potential impact on the whole ecosystem (similar to NixOS/rfcs#110 or NixOS/rfcs#148), so it wouldn't be right for it to be decided here. Anyone willing for this to happen, please open an RFC about it to bring the discussion to a more visible place.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-06-22-nix-team-meeting-minutes-65/29643/1