Add haskell's $ operator to the nix language

[Mewp]

Since I started using nix, one thing has been constantly bothering me: lack of the $ operator in the nix language.

One doesn't need to look far to find function calls with nested parentheses that would be better off without them, and I couldn't find a reason for the absence of this operator. So I implemented it to see if this would work.

The patch is simple, all tests pass, including two simple test cases added to test this operator.
I have also manually tried parsing my own nix derivations with added usages of this new operator.
That being said, I do not claim to have thought of every possible edge case.

The operator itself is the same as function application, i.e. foo a, except that foo bar baz is left associative, and foo $ bar $ baz is right associative.

Also, this PR fixes #1845 .

[edolstra]

I'm not really in favor of this. It's another syntax for Nix users to learn, while the benefit is saving a small amount of typing. Nix is not a general purpose language, so convenience features like this are probably less important than keeping the learning curve manageable.

If we add something like this, I would be more in favor of a pipe syntax (f | g | h instead of h $ g $ f).

[L-as]

Changes like this should probably go through an RFC FYI.

[max-privatevoid]

I don't think the learning curve will be impacted much by this. Using this operator is completely optional and when a user runs into a situation where it makes sense to use it, they are likely quite proficient in Nix already and working on moderately complex code.

[stale]

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

[infinisil]

To avoid duplication, I think this should be discussed in the issue here: #1845

[thufschmitt]

Closing for the same reasons as #1845. Let's get some community consensus on this first