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✏️ Editing: demo_buildcalc.pl

#!/usr/bin/perl -ws

use Parse::RecDescent;

$RD_AUTOACTION = q{ $item[-1]; # JUST TO SHOW THEY WORK WITH PRECOMPILED PARSERS
};

Parse::RecDescent->Precompile(<<'EndGrammar', "Calc", $0 );

{ use Coy; }
	{ my $lexical_var = 1; }

mult_op: '*'	{ sub { $_[0] *= $_[1] } }
	       | '/'	{ sub { $_[0] /= $_[1] } }

main: expr /\s*\Z/ { $lexical_var++ } { $item[1]->() }
	    | <error>

expr: /for(each)?/ lvar range expr
			{ my ($vname,$expr) = @item[2,4];
			  my ($from, $to) = @{$item[3]};
			  sub { my $val;
				no strict "refs";
				for $$vname ($from->()..$to->())
					{ $val = $expr->() }
				return $val;
			      }
			}
	    | lvar '=' addition
			{ my ($vname, $expr) = @item[1,3];
			  sub { no strict 'refs'; $$vname = $expr->() }
			}
	    | addition

range: "(" expr ".." expr ")"
			{ [ @item[2,4] ] }

addition: <leftop:multiplication add_op multiplication>
			{ my $add = $item[1]; sub { ::evalop($add) } }

add_op: '+'	{ sub { $_[0] += $_[1] } }
	      | '-'	{ sub { $_[0] -= $_[1] } }

multiplication: <leftop:factor mult_op factor>
			{ my $mult = $item[1]; sub { ::evalop($mult) } }

factor: number
	      | rvar
	      | '(' expr ')' { $item[2] }

number: /[-+]?\d+(\.\d+)?/	{ sub { $item[1] } }

lvar:	/\$([a-z]\w*)/		{ $1 }

rvar:	lvar			{ sub { no strict 'refs'; ${$item[1]} } }

EndGrammar

MR SKB