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for loops could be supported with a compiler fix #48

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disruptek opened this issue Jan 1, 2021 · 4 comments · May be fixed by #84
Closed

for loops could be supported with a compiler fix #48

disruptek opened this issue Jan 1, 2021 · 4 comments · May be fixed by #84
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@disruptek
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Here's the test that runs against the almost branch:

https://github.com/disruptek/cps/blob/almost/tests/fors.nim

import testes
import cps

type
  C = ref object of RootObj
    fn*: proc(c: C): C {.nimcall.}

proc trampoline(c: C) =
  var c = c
  while c != nil and c.fn != nil:
    c = c.fn(c)

testes:

  block:
    proc loop() {.cps: C.} =
      for i in 0 .. 3:
        discard
    trampoline loop()

Here's the broken rewrite; CPS doesn't know what to do with the var i statement. I don't even understand how it passes through sem successfully to reach our macro...

 16  proc foo() =
 17    block :tmp:
 18      var i
 19      ## An alias for `countup(a, b, 1)`.
 20           ## 
 21           ## See also:
 22           ## * [..<](#..<.i,T,T)
 23      var res = 0
 24      block :tmp:
 25        while res <= 3:
 26          i = T(res)
 27          discard
 28          inc(res, 1)
@disruptek disruptek added the bug Something isn't working label Jan 1, 2021
@alaviss
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alaviss commented May 3, 2021

#84 has the walkaround

@disruptek disruptek linked a pull request May 3, 2021 that will close this issue
cps: experimental support for for-loops #84
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@disruptek
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The AST is so very awful that we cannot use getImplTransformed and so this effort is being killed in favor of a more manual transformation. 💀

@zevv
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zevv commented May 23, 2021

We could always file this as a CPS issue on nim and pass it to Araq

@disruptek
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He would tell us that we made our bed when we chose to do this outside the compiler, and now we get to lie in it. And he's not wrong.

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cps: experimental support for for-loops alaviss/cps
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@disruptek @zevv @alaviss @Clyybber