On 25/10/2012, at 5:00 PM, john skaller wrote:
> It is now possible, though still a bit ugly, to define grammars with
> the action codes written as Felix templates, instead of Scheme.
>
> Here's a simple example:
>
> /////////////////////
> syntax XXX {
> x[sbor_pri] := x[>sbor_pri] "OVER" x[>sbor_pri] =># ( ?1 / ?3 );
> stmt := "WILL" sstatements "DO" ";" =># { println$ "Hello"; ??2; println$
> "Bye"; };
> }
> open syntax XXX;
>
> println$ (100.0 OVER (22.0 OVER 7.0));
>
> WILL println$ "One"; WILL println "INNER"; DO; println$ "Two"; DO ;
> //////////////////
Unfortunately this isn't enough.
I tried to do this:
////////////////
syntax LOOPS {
stmt := "FOR" sname "in" sinteger "to" sinteger "DO" sstatements "DONE" =>#
{
for ?2 in ?4 upto ?6 do ??8; done
};
}
open syntax LOOPS;
var i:int;
FOR i in 10 to 20 DO println$ i; DONE
/////////////////////////
The problem is that
for ?2 in ...
doesn't parse as Felix because ?2 is an expression, but a sname is required.
If I make ?<digits> an sname, then the ?4 and ?6 are wrong te wrong type
(it parses, the substitutions get done, but sex2flex barfs:
Parsed open of syntax extensions XXX
[sex2flx] ERROR in identifier in ( ast_literal (
"/Users/johnskaller/felix/./m.flx" 7 11
7 15 ) "double" "100.0" "100.0" )
Fatal error: exception Flx_sex2flx.Sex2FlxTypeError("identifier", _)
because 100.0 (in the quoted code) isn't an sname.
One solution to this is to write:
for ?2:sname in ?4:sexpr upto ?6:sexpr ...
i.e. to name the nonterminal you want to parse. To make that work we just add
sname := "?" sinteger ":" "sname" =># "`(PARSER_ARGUMENT ,_2)";
and so on (for every non-terminal of interest). So now this works:
/////////////////////////////
syntax XXX {
x[sbor_pri] := x[>sbor_pri] "OVER" x[>sbor_pri] =># ( ?1 / ?3 );
stmt := "WILL" sstatements "DO" ";" =># { println$ "Hello"; ??2; println$
"Bye"; };
sname := "?" sinteger ":" "sname" =># "`(PARSER_ARGUMENT ,_2)";
}
open syntax XXX;
println$ (100.0 OVER (22.0 OVER 7.0));
WILL println$ "One"; WILL println "INNER"; DO; println$ "Two"; DO ;
syntax LOOPS {
stmt := "FOR" sname "in" sinteger "to" sinteger "DO" sstatements "DONE" =>#
{
for ?2:sname in ?4 upto ?6 do ??8; done
};
}
open syntax LOOPS;
var i:int;
FOR i in 10 to 20 DO println$ i; DONE
/////////////////////////////
Notice I trickily added the sname thing into DSSL XXX, so it was open
when DSSL LOOPS got processed.
--
john skaller
[email protected]
http://felix-lang.org
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