algorithm.nim: Use func

[ee7]

To confirm: do we want to change a proc that has a proc parameter into a func? (See the first commit in this PR).

#16293 was merged, so I assume the answer is "yes".

For example, this PR changes sorted from a proc to a func. However, the below code will still compile without error even when using --experimental:strictFuncs.

import algorithm

proc myCmp(x, y: int): int =
  echo "this is a side effect"
  if x == y: return 0
  if x < y: return -1
  return 1

let foo = sorted([2, 1, 3], myCmp)
echo foo

It produces:

this is a side effect
this is a side effect
this is a side effect
this is a side effect
@[1, 2, 3]

I just want to make sure that this is what we want.

See also: #16303

[timotheecour]

hmm, I guess tests fail...

2020-12-09T17:51:16.8819350Z /Users/runner/work/1/s/lib/pure/algorithm.nim(434, 6) Error: 'sorted' can have side effects
2020-12-09T17:51:16.8836130Z an object reachable from 'a' is potentially mutated
2020-12-09T17:51:16.8863760Z /Users/runner/work/1/s/lib/pure/algorithm.nim(454, 8) the mutation is here

[ee7]

hmm, I guess tests fail...

Yeah, it's due to:

Nim/tests/views/tcan_compile_nim.nim

Line 2 in f344a70

cmd: "nim check --hints:on --experimental:strictFuncs --experimental:views compiler/nim.nim"

Because this:

bin/nim c --experimental:strictFuncs compiler/nim.nim

doesn't work with sorted as func. I thought I checked that, but oh well.

Let's see what happens with sorted as a proc. But I don't know if that's the right fix.

[timotheecour]

I've reduced the previous CI failure to #16305

[Araq]

To confirm: do we want to change a proc that has a proc parameter into a func?

No, it was an oversight by me. We don't want that. Callbacks can have effects.

[timotheecour]

To confirm: do we want to change a proc that has a proc parameter into a func?

No, it was an oversight by me. We don't want that. Callbacks can have effects.

That's the crux of #16303 and IMO we do in fact want that.

proc callCb(cb: proc(): int): int = result = cb() is safe to change to
func callCb(cb: proc(): int): int = result = cb() since all potential side effects only happen through cb, as explained in #16303 (comment)

[ee7]

To confirm: do we want to change a proc that has a proc parameter into a func?

No, it was an oversight by me. We don't want that. Callbacks can have effects.

I see. I should've asked explicitly in the sequtils PR description, rather than this one. Sorry.

Questions:

1. Could you complete this statement? "A proc in the standard library should eventually become a func if it satisfies all of the following conditions:"
2. Does anything currently block us from changing such procs into funcs?

[Araq]

If you want to continue with this, the next steps would be:

• Compile talgorithm.nim with --strictFuncs:on.
• Write tests that check wether a ref object can be used as the T in openArray[T].

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you think it is still a valid PR, please rebase it on the latest devel; otherwise it will be closed. Thank you for your contributions.