iterator: wrong + called - lib/system.nim(1102, 12): Cannot instantiate T

[mratsim]

Here is what works, uncommenting bar gives an error in system.nim

iterator zip[T1, T2](a: openarray[T1], b: openarray[T2]): (T1,T2) {.inline.} =
  let len = min(a.len, b.len)
  for i in 0..<len:
    yield (a[i], b[i])

iterator zipWith[T1,T2,T3](f: proc(u: T1, v:T2): T3, a: openarray[T1], b: openarray[T2]): T3  {.inline.} =
  for i,j in zip(a,b):
    yield f(i,j)

proc foo(args: varargs[int]) =
    for i in zip(args,args):
        echo i

## Uncommenting this fails: "Error: cannot instantiate: T"
## There is no T anywhere in the code

# proc bar(args: varargs[int]) =
#     for i in zipWith(`+`,args,args):
#         echo i


foo(1,2,3,4)

When uncommenting bar:

playground.nim(18, 22) template/generic instantiation from here
lib/system.nim(1102, 12) Error: cannot instantiate: 'T'

18, 22 is +
Line 1102,12: https://github.com/nim-lang/Nim/blob/devel/lib/system.nim#L1102

proc `+` *[T](x, y: set[T]): set[T] {.magic: "PlusSet", noSideEffect.}

It seems like instead of calling + for numbers, I'm calling + for set

(edit: correcting mistake, changed for i in for i,j in bar)

[mratsim]

Modifing to +[int] makes the error clearer:

proc bar(args: varargs[int]) =
    for i in zipWith(`+`[int],args,args):
        echo i

Error:

playground.nim(18, 21) Error: type mismatch: got (proc (x: set[int], y: set[int]): set[int]{.noSideEffect.}, varargs[int],
varargs[int])
but expected one of:
iterator zipWith[T1, T2, T3](f: proc (u: T1; v: T2): T3; a: openArray[T1]; b: openArray[T2]): T3

[Araq]

You cannot pass system.+ around as a first class proc, it's a builtin.