I'm trying to write a toy BASIC to assembler. Here's my code so far:
grammar G {
rule TOP { <stmts> }
rule stmts { <statement>* }
rule statement { <print-stmt> | <for-loop> | <assign> }
rule print-stmt { 'print' <expr> }
rule for-loop { 'for' <var> '=' <expr> 'to' <expr> <stmts>
'next' }
rule assign { <var> '=' <expr> }
token var { <[a..z]>+ }
rule expr { <expr-p> ('+' <expr-p>)* }
rule expr-p { <num> | <var> }
token num { <[0..9]>+ }
}
my $input = slurp;
#my $m = G.parse($input);
#say $m;
# print the prologue
say Q [
@ Automatically-generated assembler code
.global main
main:
@ entry point
push {ip, lr}
];
# exit and cleanup before we start putting out data
my $bye = Q [
@ exit and cleanup
mov r0, #0 @ return value 0
pop {ip, pc}
];
sub write-varnames($vnames) {
say "TODO";
say $vnames.keys.sort;
}
class A {
has $.varnames = SetHash.new;
method TOP ($/) { say "TOP"; say $bye; write-varnames
$.varnames ; }
method var ($/) { my $vname = $/.Str ; say $vname ;
$.varnames{"$vname"}++ ; }
}
my $acts = A.new;
my $ma = G.parse($input, :actions($acts));
And here's a simple test program:
for i = 1 to 3+2
sum = sum + i
next
print sum
The problem is that 'next' is taken to be a variable name, I think, as
evidenced when write-varnames is run:
(i next sum)
I guess one way around all this is never to let assignment start with a
variable name, but demand a 'let' in for assignment, as is
let sum = sum + i
But I'm wondering, is there a way to write token var in such a way that
it matches <[a..z]>+ EXCEPT when it is a keyword (print, for, to, next,
etc.)?
Is there a generally accepted way of doing all this, like defining the
keywords as seperate tokens, for example?
