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3466 :: Having trouble to generate nim code

• adrien79 (orginal) [2018-01-07T10:15:12+01:00] view original

  I'm trying to expand a template and write the resulting code into a nim file. I've tried this approach, inspired by expandMacros:

  import macros
  
  template test(msg: string, body: untyped): typed =
    body
    proc testproc(s: string) =
      echo s & ": " & $rows
    testproc(msg)
  
  macro wrapper(body: typed): untyped =
    template inner(x: untyped): untyped = x
    let
      ast = getAst(inner(body))
      code = $toStrLit(ast)
    writeFile("result.nim", code)
  
  static:
    wrapper():
      test("string"):
        let rows = 9
  Run

  This sort of works: the file result.nim contains recognizable nim code, but it is not properly indented and has weird features:

  let rows = 9
    proc testproc(s150024: string) =
    echo [&(s150024, ": ", $ rows)]
    
    testproc("string")
  Run

  Needless to say it does not compile.

  I've looked into the code of c2nim and it takes a different approach, importing compiler modules and using renderModule. I've tried that too but I can't make it work. It seems that renderModule expects a PNode and getAst returns a NimNode, but I don't understand the details.

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• Udiknedormin (orginal) [2018-01-07T15:45:22+01:00] view original

  ast = getAst(inner(body))
  code = $toStrLit(ast)
  Run

  is replaceable by:

  code = body.repr
  Run

  Other than that, it seems to be a bug as body.repr.parseStmt should be an identity and here it's not (parse error due to invalid indentation).

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• adrien79 (orginal) [2018-01-07T18:45:01+01:00] view original

  Thanks for the hint, the macro becomes simpler and better:

  macro expandToFile(filepath: string, body: typed): untyped =
    result = body # optional
    writeFile($filepath, repr(body))
  Run

  Maybe a similar mod could be applied to the source of expandMacros but I'm not sure of all the implications.

  Trying again with a devel compiler instead of 0.17.2 gets rid of the indentation bug:

  let rows = 9
  proc testproc(s143025: string) =
    echo [&(s143025, ": ", $rows)]
  
  testproc("string")
  Run

  Name mangling is not very convenient but I guess that it can't be avoided. There remains the broken echo syntax, should I file a bug against this?

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• Udiknedormin (orginal) [2018-01-07T20:46:54+01:00] view original

  I think so. I tried it with both typed and untyped macro arguments. What's funny, it works as expected for untyped ones:

  macro sth(code: untyped): untyped =
    echo code.repr
  
  sth:
    let s = 5
    echo s
  Run

  But not for typed:

  macro sth(code: typed): untyped =
    echo code.repr
  
  sth:
    let s = 5
    echo s
  Run

  I think there is a more serious bug involved here...

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