How to create an AST with ANTLR from a hierarchical key-value syntax
- by Brabster
I've been looking at parsing a key-value data format with ANTLR. Pretty straightforward, but the keys represent a hierarchy.
A simplified example of my input syntax:
/a/b/c=2
/a/b/d/e=3
/a/b/d/f=4
In my mind, this represents a tree structured as follows:
(a (b (= c 2) (d (= e 3) (= f 4))))
The nearest I can get is to use the following grammar:
/* Parser Rules */
start: (component NEWLINE?)* EOF -> (component)*;
component: FORWARD_SLASH ALPHA_STRING component -> ^(ALPHA_STRING component)
| FORWARD_SLASH ALPHA_STRING EQUALS value -> ^(EQUALS ALPHA_STRING value);
value: ALPHA_STRING;
/* Lexer Rules */
NEWLINE : '\r'? '\n';
ALPHA_STRING : ('a'..'z'|'A'..'Z'|'0'..'9')+;
EQUALS : '=';
FORWARD_SLASH : '/';
Which produces:
(a (b (= c 2))) (a (b (d (= e 3)))) (a (b (d (= f 4))))
I'm not sure whether I'm asking too much from a generic tool such as ANTLR here, and this is as close I can get with this approach. That is, from here I consume the parts of the tree and create the data structure I want by hand.
So - can I produce the tree structure I want directly from a grammar? If so, how? If not, why not - is it a technical limitation in ANTLR or is it something more CS-y to do with the type of language involved?
