[spytheman]

• all: support short lambda expressions like a.sorted(|x,y| x > y), in all callsites that accept a fn callback
• ci: fix v build-tools
• fixes for vlib/v/parser/tests/anon_sum_type_multi_return_err.vv

[JalonSolov]

Hmm... f(||42) looks like an error, to me. What's the use of the || if there are no variables listed between them?

[spytheman]

import os

fn f( cb fn() string ) string { return cb() }

dump( f(fn() string { return os.args[0] }) )

// the same, just shorter:
dump( f(||os.args[0]) ) 

prints:

[a.v:5] f(anon_fn): /v/vnew/a
[a.v:6] f(|| os.args[0]): /v/vnew/a

i.e. using functions/expressions for callbacks, that get their values from external sources

[JalonSolov]

Must be too subtle for me... I don't get why the || is there, if there are no variables involved.

[spytheman]

Must be too subtle for me... I don't get why the || is there, if there are no variables involved.

Because otherwise it would not be a lambda expression/function to call; it would get evaluated immediately.

It may be easier to see with:

import rand
fn f( cb fn() int ) string { return 'randoms: ${cb()}, ${cb()}, ${cb()}' }
dump( f(||rand.int()/1_000_000) )

which will produce something like:

[r.v:3] f(|| rand.int() / 1000000): randoms: 501, 657, 1345

i.e. the passed lambda expression will be executed 3 times, each with a different result.

Note, that the above is equivalent to this, just shorter:

import rand
fn f( cb fn() int ) string { return 'randoms: ${cb()}, ${cb()}, ${cb()}' }
dump( f( fn() int { return rand.int()/1_000_000 } ))

[JalonSolov]

So the || is a trigger to show that it is a lambda as opposed to a simple anonymous function.

Still looks strange...

[spytheman]

Still looks strange...

I agree. It is just the logical reduction of the lambda syntax, for when the anon fn has 0 args.

[daemonu]

awesome feature. could we maybe use _ if lambda doesn't need args instead of or ||?

[JalonSolov]

Probably the same idea... it would be identified as an anonymous function instead of a lambda, without the ||.

[dumblob]

Looking at this I actually sort of like this tiny syntax sugar.

Shouldn't we also emphasize in the documentation that it is actually not a true lambda expression as known from other languages (which distinguish between a function and a lambda) but just syntax sugar for plain old V function definition?