nimforum mirror - Bind not working in Generic Procs.

solo989 (orginal) [2019-07-19T18:49:36+02:00] view original

I noticed bind no longer works in generic procs. I came up with a macro that can be used as a pragma workaround.

macro genProcWithBind*(a : untyped) : untyped =
  let templateSym = genSym(nskTemplate)
  let body = a[6].copy()
  let newProc = a.copy()
  newProc[6] = quote do:
    `templateSym`()
  result = newStmtList()
  result.add quote do:
    template `templateSym`() : untyped =
      `body`
  result.add newProc

You use it like this.

when false:
  #now works with bind
  proc sort*[T](a : T) {.genProcWithBind.} =
    bind privateSort
    privateSort(a)
  #turns into this
  template genSymed() : untyped =
    bind privateSort
    privateSort(a)
  proc sort*[T](a : T) =
    genSymed()

Should work with mixin too. I though it might be useful; maybe even add it to the system or macros module with a better name then I came up with.

mratsim (orginal) [2019-07-19T20:03:27+02:00] view original

You should probably open a regression issue in the tracker with a minimal example

solo989 (orginal) [2019-07-20T09:30:59+02:00] view original

Here's a better example of what I'm talking about.

Imagine you have two files foreignFile.nim and myFile.nim.

foreignFile.nim

template p[T:int|float](a : T) =
  echo "Number:" & $a

template p(a : string) =
  echo "String:" & a

proc printVar*[T:int|float|string](a : T) =
  p(a)

All the templates printVar should call are already defined but p isn't bound so it can potentially use new templates/procs/etc defined in the future.

myFile.nim

import foreignFile

var x = 0

template p(a : int) =
  x += a
  echo x

p(7)

printVar(5)
printVar(5.0)
printVar("5.0")

In this example you've inadvertently overwritten p from myFile when aProc is passed an int. It will echo 12 instead of Number:5. You only wanted to call your new p definition directly. In this case the generic printVar proc should probably be three seperate printVar definitions instead of

proc printVar*[T:int|float|string](a : T)

Araq (orginal) [2019-07-21T17:40:08+02:00] view original

It works as designed, https://nim-lang.org/docs/manual.html#symbol-lookup-in-generics-open-and-closed-symbols

https://nim-lang.org/docs/manual.html#generics-bind-statement

solo989 (orginal) [2019-07-22T02:24:22+02:00] view original

Your example doesn't work on my compiler.

proc p(a : int) =
  echo a

proc printVar*[T:int|float|string](a : T) =
  bind p
  p(a)

printVar(5)

nim

gives Error: invalid expression: bind p

Oddly enough if you don't call the printVar at all it doesn't give you an error.

compiled with nim c test.nim

I've actually had this problem for a few versions but I assumed you already knew about it before.

solo989 (orginal) [2019-07-22T02:40:29+02:00] view original

also gives me the same error.

solo989 (orginal) [2019-07-22T05:14:31+02:00] view original

I think I know why this bug may have slipped through the cracks. None of the tests in Nimtests check to see if the bind command works in generic procs as well as templates. Also it sounds like other people aren't having this problem and it might be a build specific bug.

solo989 (orginal) [2019-07-22T05:23:20+02:00] view original

I would be interested to see if anyone else has encountered this error.

proc p(a : int) =
  echo a

proc printVar*[T:int|float|string](a : T) =
  bind p
  p(a)

printVar(5)

Run this little bit of code and if it spits back

Error: invalid expression: bind p

then we have the same bug.

mratsim (orginal) [2019-07-22T11:42:29+02:00] view original

The playground fails as well.

Mirror of forum.nim-lang.org

5031 :: Bind not working in Generic Procs.