Hey all,

I'm working on an implementation of JOY programming language for fun (I highly recommend the language and would love to discuss it with other monks!)

My current task: I'm splitting up an input file into a list of tokens. I've slurped the whole thing into a string and am trying to split it.

The string should be split at each whitespace (\s+) unless the space is between unescaped parentheses. There will only one level of parentheses, so no need to worry about deep nesting.
For example, 
this    is (some more) 
JOY code

[download]
should split into 
"this", "is", "(some more)", "JOY", "code"

[download]
I thought I had a good solution: split on whitespace when we can look behind for a ) and ahead for a (. 
                             
# match when between unescaped reverse parens                         
+          
# ..or start/end of string                                            
+          
@script = split
/
 (?<=           #lookbehind (only remove whitespaces)                 
+                  
  (^|           #for start of string or                               
+          
   (?<!\\) \) ) #unescaped rparen followed by                         
+          
  .*?           #stingy other chars                                   
+          
 )

 \s+            #some spaces, to be removed                           
+ 

 (?=            #lookahead                                            
+          
  .*?           #stingy other chars                                   
+          
  ($|           #end of string or                                     
+          
   (?<!\\) \( ) #unescaped lparen                                     
+          
 )
/xs, $script;

[download]
but when I run this, I get "Variable length lookbehind is not implemented in regex".

So, what would you do? I'm not sure it's possible with regular expressions anymore (a challenge!) since lookbehind was my way of not removing anything but the whitespace... should I keep regex hacking, or move on?

Thanks,

~dewey

In reply to Splitting on unusual regex by dewey

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