Variable::Declaration example

example.md

use strict;
use warnings;
use feature qw/say/;

use Variable::Declaration;
use Types::Standard '-all';

let $foo = 'hello';
say $foo; # => hello

let Str $str1 = {};
# ERROR: Reference {} did not pass type constraint "Str"

let Str $str2 = 'hello';
$str2 = {};
# ERROR: Reference {} did not pass type constraint "Str"

let ($bar, $baz) = ('hello', 'world');
let (Int $a, Int $b) = 1..2;

sub hello {
    let Str $message = shift;
    say "HELLO $message";
}

hello('OKINAWA!'); # => HELLO OKINAWA!
hello({});
# ERROR: Reference {} did not pass type constraint "Str"


# `static`
#   is equivalent to `state` with type constraint

sub counter {
    static $i = 0;
    $i++;
}
say counter() for 1..10;



#
# `const`
#   is equivalent to `my`
#   with type constraint and data lock
#

const $pi = 3.14;
$pi = 3.141519;
# ERROR: Modification of a read-only value attempted

use Variable::Declaration level => 2; # default
use Types::Standard qw/Int/;

{
    let Int $i = 'hello';
    # ERROR: Value "hello" did not pass type constraint "Int"
}

{
    let Int $i = 123;
    $i = 'hello';
    # ERROR: Value "hello" did not pass type constraint "Int"
}

use Variable::Declaration level => 1;
use Types::Standard qw/Int/;

{
    let Int $i = 123;
    $i = 'hello'; # *NO* Error
}

{
    let Int $i = 'hello';
    # ERROR: Value "hello" did not pass type constraint "Int"
}

use Variable::Declaration level => 0;
use Types::Standard qw/Int/;

{
    let Int $i = 123;
    $i = 'hello'; # *NO* Error
}

{
    let Int $i = 'hello';
    # *NO* Error
}

#
# FAIL CASE...
#

(let $a)
# eq (;;my $a)

if (let $a = 'hello') { }

for let $a (@list)