Using concatenate dolar before parentheses

[jcubic]

I have issue with this grammar:

content = text:$(image  / inline_text / list_item)+ nl:[\n]? {
    return text + (nl || '');
}

This doesn't work and don't give any error. It works when the group is in separated rule.

You can test the grammar on this CodePen demo:

https://codepen.io/jcubic/pen/zYLvPQa?editors=1000

If you add $ and replace text.join('') with text, the parser just output input text.

[hildjj]

This works as designed at the moment. Changing it would break existing grammars.

This comes up most often for me in grammars that decode things like escaped quotes:

string 
  = DQUOTE s:char* DQUOTE { 
    return s.join('');
  } 
  
DQUOTE 
  = '"'
  
char 
  = ![\\"] @. // Anything but backslash or dquote
  / '\\' @'"'

The docs say:

$ expression

Try to match the expression. If the match succeeds, return the matched 
text instead of the match result.

If you need to return the matched text in an action, you can use the 
text() function, but returning a labeled $ expression is sometimes more clear.

Which makes it pretty clear that $ is doing the same thing as text(), but I'm very open to making this more explicit or clear if anyone wants to suggest more or different text.

[jcubic]

Ok I expect that this do work:

inline_content = image  / inline_text / list_item
    
content = text:$inline_content+ nl:[\n]? {
    return text + (nl || '');
}

same as:

inline_text = bold / italic / link / [^\n]

header = '#'+ ' '* text:$inline_text* [\n] {
    return '[[b;;]' + text + ']';
}

But the first grammar makes the parser ignore all the rules.

Without dollar, it works fine, but I need to use text.join(''). I don't see what is the different between those two rules.

[hildjj]

Ah, I think I see where your mental model doesn't match what Peggy is doing. The $ does not operate on the results of the rules that are returned. It returns the slice of text from the original string that matched the rules.

[jcubic]

I'm not sure if I understand.

[hildjj]

Here's a simplified example:

Foo = bar+

bar = "bar" { return "baz" }

The input "barbar" will give the output ['baz', 'baz'].

When you change Foo to be $bar+, the output is "barbar". The $ discards whatever the bar rule returns and instead returns matching text. The bar rule still runs twice, still matches twice.

[jcubic]

Ok, now I understand, it just that I used markdown header and list wrong in my input code,

If I use:

## [xxx](https://example.com)

It works the same, and the code land in output.