Function + comment = error

AlanHK · 21st February 2009, 07:44

I found that if in any function definition I have a comment after the function name and before the body, it throws an error:

Code:

AVISource("Garden.avi",false)
zz()

Function zz(clip a) # useless function
{return a}

same for

Code:

Function zz(clip a) 
# useless function
{return a}

The error is "expected "{"

Which was an unexpected error, at least for me.

tebasuna51 · 21st February 2009, 10:27

You are right.
Maybe a 2.58 issue?
With 2.57 was OK.

BTW this work:

Code:

Function zz(clip a) { # useless function
return a}

Gavino · 21st February 2009, 17:32

Quote:

Originally Posted by tebasuna51

Maybe a 2.58 issue?
With 2.57 was OK.

Are you sure? I tried with 2.57 and got exactly the same behaviour as 2.58.

Looks like this is a 'feature' of the tokeniser. Newlines are skipped if the next token is '{', but not when there is a comment present.

Using the new /* ... */ form of comment available in 2.58 does work, ie

Code:

Function zz(clip a) /* useless function */
{return a}

is accepted.

Gavino · 21st February 2009, 19:26

It's not clear to me if this is intended behaviour or an oversight.
However, since newlines are allowed before a '{', it seems inconsistent not to allow a comment here too.

I believe a simple fix is to change the code that handles #-comments (in Tokenizer::NextToken(), tokenizer.cpp) from

Code:

      // skip from # to end of line (comment)
      while (*pc != 0 && *pc != '\n' && *pc != '\r')
        pc++;
      break;

to

Code:

      // skip from # to end of line (comment)
      while (*pc != 0 && *pc != '\n' && *pc != '\r')
        pc++;
      if (*pc == 0) break;
      continue;

This would force the newline terminating the comment to be treated like any other newline.

As an added bonus, it would also allow a '\' continuation on the line following a comment, something not possible at the moment.
Two extensions for the price of one.

Gavino · 7th December 2009, 01:06

Looking further at this, my suggested fix above would only be a partial solution, since it doesn't help when the comment (even a new-style one) is on a different line to the function header, eg

Code:

function zz(clip a)
/* some inane comment ... */
{ ...

A better approach is to do it in the parser rather than hacking the lexer with even more special cases, by changing the code in ScriptParser::ParseBlock() from

Code:

  if (braced)
    Expect('{');

to

Code:

  if (braced) {
    // allow newlines (and hence comments) before '{'
    while (tokenizer.IsNewline())
      tokenizer.NextToken();
    Expect('{');
  }

The code in Tokenizer::NextToken()

Code:

      } else if (*pc == '{') {
        break;

could then safely be removed. (probably!

)

The revised fix no longer extends to allow a '\' continuation on the line following a comment, but I'm not sure that is desirable anyway.

21st February 2009, 07:44	#1 \| Link
AlanHK Registered User Join Date: May 2006 Posts: 237	Function + comment = error I found that if in any function definition I have a comment after the function name and before the body, it throws an error: Code: AVISource("Garden.avi",false) zz() Function zz(clip a) # useless function {return a} same for Code: Function zz(clip a) # useless function {return a} The error is "expected "{" Which was an unexpected error, at least for me.

21st February 2009, 10:27	#2 \| Link
tebasuna51 Moderator Join Date: Feb 2005 Location: Spain Posts: 6,915	You are right. Maybe a 2.58 issue? With 2.57 was OK. BTW this work: Code: Function zz(clip a) { # useless function return a} __________________ BeHappy, AviSynth audio transcoder.

21st February 2009, 19:26	#4 \| Link
Gavino Avisynth language lover Join Date: Dec 2007 Location: Spain Posts: 3,431	It's not clear to me if this is intended behaviour or an oversight. However, since newlines are allowed before a '{', it seems inconsistent not to allow a comment here too. I believe a simple fix is to change the code that handles #-comments (in Tokenizer::NextToken(), tokenizer.cpp) from Code: // skip from # to end of line (comment) while (pc != 0 && pc != '\n' && pc != '\r') pc++; break; to Code: // skip from # to end of line (comment) while (pc != 0 && pc != '\n' && pc != '\r') pc++; if (*pc == 0) break; continue; This would force the newline terminating the comment to be treated like any other newline. As an added bonus, it would also allow a '\' continuation on the line following a comment, something not possible at the moment. Two extensions for the price of one.

7th December 2009, 01:06	#5 \| Link
Gavino Avisynth language lover Join Date: Dec 2007 Location: Spain Posts: 3,431	Looking further at this, my suggested fix above would only be a partial solution, since it doesn't help when the comment (even a new-style one) is on a different line to the function header, eg Code: function zz(clip a) /* some inane comment ... / { ... A better approach is to do it in the parser rather than hacking the lexer with even more special cases, by changing the code in ScriptParser::ParseBlock() from Code: if (braced) Expect('{'); to Code: if (braced) { // allow newlines (and hence comments) before '{' while (tokenizer.IsNewline()) tokenizer.NextToken(); Expect('{'); } The code in Tokenizer::NextToken() Code: } else if (pc == '{') { break; could then safely be removed. (probably! ) The revised fix no longer extends to allow a '\' continuation on the line following a comment, but I'm not sure that is desirable anyway. Last edited by Gavino; 7th December 2009 at 01:10.