Merge pull request #325 from ros2/idl-stage-4

add lark-based grammar

rosidl_parser/rosidl_parser/common.lark

@@ -0,0 +1,48 @@
+//
+// Numbers
+//
+
+DIGIT: "0".."9"
+HEXDIGIT: "a".."f"|"A".."F"|DIGIT
+
+INT: DIGIT+
+SIGNED_INT: ["+"|"-"] INT
+DECIMAL: INT "." INT? | "." INT
+
+// float = /-?\d+(\.\d+)?([eE][+-]?\d+)?/
+_EXP: ("e"|"E") SIGNED_INT
+FLOAT: INT _EXP | DECIMAL _EXP?
+SIGNED_FLOAT: ["+"|"-"] FLOAT
+
+NUMBER: FLOAT | INT
+SIGNED_NUMBER: ["+"|"-"] NUMBER
+
+//
+// Strings
+//
+//STRING: /"(\\\"|\\\\|[^"\n])*?"i?/
+STRING_INNER: ("\\\""|/[^"]/)
+ESCAPED_STRING: "\"" STRING_INNER* "\""
+
+
+//
+// Names (Variables)
+//
+LCASE_LETTER: "a".."z"
+UCASE_LETTER: "A".."Z"
+
+LETTER: UCASE_LETTER | LCASE_LETTER
+WORD: LETTER+
+
+CNAME: ("_"|LETTER) ("_"|LETTER|DIGIT)*
+
+
+//
+// Whitespace
+//
+WS_INLINE: (" "|/\t/)+
+WS: /[ \t\f\r\n]/+
+
+CR : /\r/
+LF : /\n/
+NEWLINE: (CR? LF)+