DParserGen 0.1.0

[Tim]

On Sunday, 7 May 2023 at 18:38:09 UTC, max haughton wrote:
> Which parts of the D grammar require backtracking?

Backtracking is used to resolve some ambiguities in the grammar. 
The ambiguities could probably also be resolved with other 
solutions like lookahead.

You can find all nonterminals, which use backtracking, by 
searching for "@backtrack" in the grammar file: 
https://github.com/tim-dlang/dparsergen/blob/master/examples/d/grammard.ebnf

One example is distinguishing types and expressions in 
TypeidExpression, TemplateArgument and other nonterminals. The 
parser first tries to parse it as a type and then as an 
expression. The parameter of the template instance 
"Template!(x*[0][0])" could be a type or an expression. As a type 
it would be an array of an array of a pointer to "x". As an 
expression it would be "x" multiplied by "[0][0]", which is 0. 
The parser will always parse this as a type.

For statements it also first tries to parse a declaration and 
then an expression, so "x*y;" is always parsed as a declaration. 
The same ambiguity exists for IfCondition.