Move README.html to gitweb/

[phdru.name/cgi-bin/blog-ru/search-tags.git] / parser / grammar.ebnf

diff --git a/parser/grammar.ebnf b/parser/grammar.ebnf
index b657738ad5f30a6ab29508f8364b212faffa4708..935e6a4d3477f7bfa557fde4a28c5dca83786eaa 100644 (file)
--- a/parser/grammar.ebnf
+++ b/parser/grammar.ebnf
@@ -1,4 +1,4 @@
-# Grammar rules for tag searching; EBNF.
+# Grammar rules for tag searching
 
 # The grammar defines expressions in the following forms:
 #  TAG - search blog posts that contain the tag;
@@ -11,26 +11,38 @@
 # Allowed operators: conjunction - & && AND and
 #                    disjunction - | || OR or
 #                    negation    - ! NOT not
+# Usual priority: NOT recognized before AND, AND before OR.
 # This  is a simple version of the grammar and it allows
-# rather stupid expressions, like !!TAG or ((TAG))
+# rather stupid expressions, like (TAG) or ((TAG)) or !(!(TAG)).
 
-@@grammar :: Tags
+expression = or_expression / aterm_expression
 
-start = expression $ ;
+or_expression = aterm_expression or_op expression
 
-expression = (
-           | expression and_op expression
-           | expression or_op expression
-           | not_op expression
-           | expression_parens
-           | name ) ;
+and_expression = term_expression and_op aterm_expression
 
-expression_parens = '(' expression ')' ;
+not_expression = not_op space0 (parens_expression / name)
 
-name = /[a-z][a-z0-9_]+/ ;
+aterm_expression = and_expression / term_expression
 
-and_op = '&' | '&&' | 'AND' | 'and' ;
+term_expression = not_expression / parens_expression / (name space_b4letter)
 
-or_op = '|' | '||' | 'OR' | 'or' ;
+parens_expression = "(" space0 expression space0 ")"
 
-not_op = '!' | 'NOT' | 'not' ;
+and_op = (space0 ("&&" / "&") space0) / (space0 ("AND" / "and") space_b4letter)
+
+or_op = (space0 ("||" / "|") space0) / (space0 ("OR" / "or") space_b4letter)
+
+not_op = (space0 "!" space0) / (space0 ("NOT" / "not") space_b4letter)
+
+letter = ~"[a-z]"i
+
+name = ~"[a-z][a-z0-9_]*"
+
+space_b4letter = (space1 &letter) / space0
+
+space0 = ~" *"
+
+space1 = ~" +"
+
+# vim: set ft=text :