[antlr-interest] more on left-recursive rules

[Alan Rooks]

Terence Parr wrote:
> Got these examples into unit tests. :) feeling good.
> Ter
> 
> // simple, no AST
> a : a ID
>   | ID  ;
> 
> -------------
> 
> declarator
>         : declarator '['^ e ']'!
>         | declarator '['^ ']'!
>         | declarator '('^ ')'!
>         | '*'^ declarator
>         | '('! declarator ')'!
>         | ID
>         ;
> 
> 
> declarator
>         : declarator '[' e ']' -> ^('[' declarator e)
>         | declarator '[' ']' -> ^('[' declarator)
>         | declarator '(' ')' -> ^('(' declarator)
>         | '*' declarator -> ^('*' declarator) 
>         | '(' declarator ')' -> declarator
>         | ID -> ID
>         ;
> 
> 		String[] tests = {
> 			"a",		"a",
> 			"*a",		"(* a)",
> 			"**a",		"(* (* a))",
> 			"a[3]",		"([ a 3)",
> 			"b[]",		"([ b)",
> 			"(a)",		"a",
> 			"a[]()",	"(( ([ a))",
> 			"a[][]",	"([ ([ a))",
> 			"*a[]",		"(* ([ a))",
> 			"(*a)[]",	"([ (* a))",
> 		};
> 
> ---------------
> 
> e : e '.'^ ID
>   | e '.'^ 'this'
>   | '-'^ e
>   | e '*'^ e
>   | e ('+'^|'-'^) e
>   | INT
>   | ID
>   ;
> 
> 		String[] tests = {
> 			"a",		"a",
> 			"1",		"1",
> 			"a+1",		"(+ a 1)",
> 			"a*1",		"(* a 1)",
> 			"a.b",		"(. a b)",
> 			"a.this",	"(. a this)",
> 			"a+b*c",	"(+ a (* b c))",
> 			"a.b+1",	"(+ (. a b) 1)",
> 			"-a",		"(- a)",
> 			"-a+b",		"(+ (- a) b)",
> 			"-a.b",		"(- (. a b))",
> 		};

What do you get for "a-b+c"?

I hope it's "(+ (- a b) c)" and not "(- a (+ b c)".

(The former being left associative and the latter being right.  Most people 
would expect a-b+c to be evaluated left, as in (a-b)+c.  Right?  :-)

Alan
--
Alan Rooks
Software Tools Development
ON Semiconductor