Wolfram Language Paclet Repository
Community-contributed installable additions to the Wolfram Language
Wolfram`Parser`
RecRef  |
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▪
RecRef
"Recursive"
▪
It is therefore safe to build a before or after the matching - a forward reference into a not-yet-defined production is exactly the point - and to use it in any number of places. Each occurrence re-enters the same production.
RecRef
▪
One cell, many references: an item that can recur on either side of a separator just drops a at each spot.
RecRef[cell]
▪
Make the recursion target a of concrete alternatives rather than a production that begins with a nullable parser; re-entering at a nullable prefix can match empty and bail instead of recursing.
Examples
(3)
Basic Examples
(1)
Build a reference before the production exists, then close the loop with - a self-describing s-expression grammar where an expression is an atom or a parenthesised list of expressions:
In[1]:=
expr=
[];ref=
[expr];
expr,
["[a-z]+"],
"("],
ref,
[" "],
[")";
[ref,"(a (b c) d)"]
 | RecCell |
| RecRef |
 | SetRec |
 | ParseChoice |
 | ParseRegex |
| ParseBetween |
| ParseLiteral |
| ParseSepBy |
| ParseLiteral |
| ParseLiteral |
 | Parse |
Out[1]=
{a,{b,c},d}
The same reference parses a bare atom - the recursion is simply not entered:
In[2]:=
| Parse |
Out[2]=
x
Scope
(1)
Possible Issues
(1)
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""