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The iterative style is the preferred style to use with Semantic. It relies on an iterative parser back-end mechanism which parses start nonterminals one at a time and automagically skips unexpected lexical tokens in input.
Compared to rule-based iterative functions (see Bison style), iterative parsers are better in that they can handle obscure errors more cleanly.
Each start nonterminal must produces a raw tag by calling a
TAG-like grammar macro with appropriate parameters. See also
Start nonterminals.
Then, each parsing iteration automatically translates a raw tag into expanded tags, updating the raw tag structure with internal properties and buffer related data.
After parsing completes, it results in a tree of expanded tags.
The following example is a snippet of the iterative style Java grammar provided in the Semantic distribution in the file semantic/wisent/java-tags.wy.
… ;; Alternate entry points ;; - Needed by partial re-parse %start formal_parameter … ;; - Needed by EXPANDFULL clauses %start formal_parameters … formal_parameter_list : PAREN_BLOCK (EXPANDFULL 1ドル formal_parameters) ; formal_parameters : LPAREN () | RPAREN () | formal_parameter COMMA | formal_parameter RPAREN ; formal_parameter : formal_parameter_modifier_opt type variable_declarator_id (VARIABLE-TAG 3ドル 2ドル nil :typemodifiers 1ドル) ;
It shows the use of the EXPANDFULL grammar macro to parse a
‘PAREN_BLOCK’ which contains a ‘formal_parameter_list’.
EXPANDFULL tells to recursively parse ‘formal_parameters’
inside ‘PAREN_BLOCK’. The parser iterates until it digested all
available input data inside the ‘PAREN_BLOCK’, trying to match
any of the ‘formal_parameters’ rules:
At each iteration it will return a ‘formal_parameter’ raw tag,
or nil to skip unwanted (single ‘LPAREN’ or ‘RPAREN’
for example) or unexpected input data. Those raw tags will be
automatically expanded by the iterative back-end parser.
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