- examples/EBNF/grammar_tests: grammar tests completed

examples/EBNF/example_2.dsl

-# EBNF-Grammar in EBNF
+# An alternative EBNF-Grammar
+# Please note: This does not work with the current ebnf.py
+# TODO: Transform ASTs stemming from this grammar to ASTs
+#       that DHParser.ebnf.EBNFCompiler can compile.
 
 @ comment    = /#.*(?:\n|$)/                    # comments start with '#' and eat all chars up to and including '\n'
 @ whitespace = /\s*/                            # whitespace includes linefeed
 @ literalws  = right                            # trailing whitespace of literals will be ignored tacitly
 
+#: top-level
+
 syntax     = [~//] { definition | directive } §EOF
 definition = symbol §"=" expression
 directive  = "@" §symbol "=" (regexp | literal | symbol) { "," (regexp | literal | symbol) }
 
+#: components
+
 expression = term { "|" term }
 term       = { ["§"] factor }+                       # "§" means all following factors mandatory
-factor     = [flowmarker] [retrieveop] symbol !"="   # negative lookahead to be sure it's not a definition
-           | [flowmarker] literal
-           | [flowmarker] plaintext
-           | [flowmarker] regexp
-           | [flowmarker] whitespace
-           | [flowmarker] oneormore
-           | [flowmarker] group
-           | [flowmarker] unordered
-           | repetition
-           | option
+factor     = [flowmarker] [retrieveop] symbol [suffix] !"="
+           | [flowmarker] (  literal
+                           | plaintext
+                           | regexp
+                           | whitespace
+                           | group
+                           | unordered ) [suffix]
+
+#: flow-operators
 
 flowmarker = "!"  | "&"                         # '!' negative lookahead, '&' positive lookahead
            | "-!" | "-&"                        # '-' negative lookbehind, '-&' positive lookbehind
 retrieveop = "::" | ":"                         # '::' pop, ':' retrieve
 
+#: groups
+
 group      = "(" §expression ")"
-unordered  = "<" §expression ">"                # elements of expression in arbitrary order
-oneormore  = "{" expression "}+"
-repetition = "{" §expression "}"
-option     = "[" §expression "]"
+unordered  = "{" §expression "}"                # elements of expression in arbitrary order
+
+#: suffixes
+
+oneormore  = "+"
+repetition = "*"
+option     = "?"
+
+#: leaf-elements
 
 symbol     = /(?!\d)\w+/~                       # e.g. expression, factor, parameter_list
-literal    = /"(?:[^"]|\\")*?"/~                # e.g. "(", '+', 'while'
-           | /'(?:[^']|\\')*?'/~                # whitespace following literals will be ignored tacitly.
-plaintext  = /`(?:[^"]|\\")*?`/~                # like literal but does not eat whitespace
-regexp     = /\/(?:\\(\/)|[^\/])*?\//~            # e.g. /\w+/, ~/#.*(?:\n|$)/~
+literal    = /"(?:(?<!\\)\\"|[^"])*?"/~         # e.g. "(", '+', 'while'
+           | /'(?:(?<!\\)\\'|[^'])*?'/~         # whitespace following literals will be ignored tacitly.
+plaintext  = /`(?:(?<!\\)\\`|[^"])*?`/~         # like literal but does not eat whitespace
+regexp     = /\/(?:(?<!\\)\\(?:\/)|[^\/])*?\//~     # e.g. /\w+/, ~/#.*(?:\n|$)/~
 whitespace = /~/~                               # insignificant whitespace
 
 EOF = !/./