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2360 :: [macro] Adding echo to a function

• mora (orginal) [2016-07-06T11:39:56+02:00] view original

  Hi,

  I'm trying to add an echo("OK") to the end of a function. Here are the attempts. Could you please advise how to do this?

  Thanks,

  Peter

  import macros
  
  # Illegal storage access. (Attempt to read from nil?)
  macro addEcho1(s: stmt): stmt =
    s.body.add(newCall("echo", newStrLitNode("OK")))
    result = s
  
  proc f1() {.addEcho1.} =
    let i = 1+2
    echo i
  
  # Internal error
  macro addEcho2(s: stmt): stmt =
    s.body.add(newCall(bindSym"echo", newStrLitNode("OK")))
    result = s
  
  proc f2() {.addEcho2.} =
    let i = 1+2
    echo i
  
  # Illegal storage access. (Attempt to read from nil?)
  macro addEcho3(s: stmt): stmt =
    s.body.add(parseExpr("echo \"OK\""))
    result = s
  
  proc f3() {.addEcho3.} =
    let i = 1+2
    echo i
  
  # internal error: expr(nkClosedSymChoice); unknown node kind
  macro addEcho4(s: stmt): stmt =
    s.body.add(newCall(bindsym"write",bindsym"stdout", newStrLitNode("OK\n")))
    result = s
  
  proc f4() {.addEcho4.} =
    let i = 1+2
    echo i
  
  # Illegal storage access. (Attempt to read from nil?)
  macro addEcho5(s: stmt): stmt =
    s.body.add(parseExpr("stdout.write \"OK\\n\" "))
    result = s
  
  proc f5() {.addEcho5.} =
    let i = 1+2
    echo i
  Run

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• flyx (orginal) [2016-07-06T13:49:57+02:00] view original

  import macros
  
  macro addEcho(s: untyped): stmt =
    s.body.add(newCall("echo", newStrLitNode("OK")))
    result = s
  
  proc f1() {.addEcho.} =
    let i = 1+2
    echo i
  Run

  You have to use untyped because with stmt, Nim seems to create a symbol f1 beforehand and then gets confused about it because you return a proc f1 again with the same signature. This should probably be reported as bug, because it should at least generate a sensible error message.

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• mbaulch (orginal) [2016-07-06T14:31:55+02:00] view original

  Hopefully, expr and stmt will be deprecated soon. The manual seems to imply this will happen.

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• mora (orginal) [2016-07-06T19:02:31+02:00] view original

  Thanks, untyped works. However, I don't think that the source of the errors is the duplicated funtion signature, because the following code works and prints 3 twice:

  macro addEcho1(s: stmt): stmt =
    s.body.add(s.body[1])
    result = s
  
  proc f1() {.addEcho1.} =
    let i = 1+2
    echo i
  f1()
  Run

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