Raku Books / Creating a Compiler in Raku / Working on Grammar

Executable

The first thing to do in this chapter is to make the translator (which latter will become a compiler) a proper executable program so that we can easily call it from the command line and pass the filename containing a Lingua program to it:

./lingua my-prog.lng

The lingua executable has to check whether you passed the filename and if the file exists, and after that it parses and executes the input program. Here is the whole code:

#!/usr/bin/env raku

use lib 'lib';
use Lingua;
use LinguaActions;

error('Usage: ./lingua <filename>') unless @*ARGS.elems;

my $filename = @*ARGS[0];
error("Error: File $filename not found") unless $filename.IO.f;

my $code = $filename.IO.slurp();
my $result = Lingua.parse($code, :actions(LinguaActions));
say $result ?? 'OK' !! error('Error: parse failed');

sub error($message) {
    note $message;
    exit;
}

The error function prints an error message and terminates the program. It uses the note built-in function, which behaves like say but sends the output to the standard error stream. The die routine is not used here as it prints additional information about the location of the error, which is not really needed in this case. Suppressing the extra output of die needs roughly the same number of lines as introducing a new function.

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