Erlang (programming language)/Tutorials/Yecc
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Making Parsers with yecc
Yecc is an erlang version of yacc.
We have a BNF grammar in a source file ending in .yrl yrl means yecc rule list. We can parse simple a simple xhtml file using yecc. (Of course a more powerful way to do xml in erlang is xmerl)
html.yrl source:
Nonterminals tag elements element start_tag end_tag .
Terminals 'atom' '<' '>' '/'.
Rootsymbol tag.
tag ->
start_tag tag end_tag :
['$1', '$2', '$3'].
tag ->
start_tag tag tag end_tag :
['$1', '$2', '$3', '$4'].
tag ->
start_tag elements end_tag :
['$1', {'contents','$2'}, '$3'].
tag ->
start_tag end_tag :
['$1','$2'].
start_tag -> '<' 'atom' '>' : {'open','$2'}.
end_tag -> '<' '/' 'atom' '>' : {'close','$3'}.
elements -> element : ['$1'].
elements -> element elements : ['$1', '$2'].
element -> atom : '$1'.
% yecc:yecc("html.yrl","html_parser.erl").
% c(html_parser).
% f(B), {_,B,_} =
% erl_scan:string(
% "<html><head></head><body>hello_world</body></html>").
% html_parser:parse(B).