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A two-number arithmetic object — construct it with an x and a y, then ask for their sum, difference, product or quotient.

Version

0.0.1 github:manwar

Depends

none beyond the core

License

Artistic-2.0

Its own test suite

1 file, green

Checked

2026-09-15 against Raku++ 3.28.0 and Rakudo 2026.08

Where it lives

raku.land · source

Install it #

$ rakupp install Calculator

zef install Calculator writes the same store; either installer leaves the module usable by both engines.

What it is for #

This is a first distribution — the kind written to learn the packaging, the test harness and the metadata rather than to solve a problem. It holds two numbers and offers the four arithmetic operations on them.

It is in the handbook because it is short enough to read in full and because its constructor makes a decision worth understanding before you copy the pattern.

Using it #

use Calculator;

my $c = Calculator.new(x => 10, y => 3);
say 'x = ', $c.x, '   y = ', $c.y;
say '';
say 'add       -> ', $c.add;
say 'substract -> ', $c.substract;
say 'multiply  -> ', $c.multiply;
say 'divide    -> ', $c.divide, '   (a ', $c.divide.^name, ', exactly ',
    $c.divide.nude.join('/'), ')';

x = 10   y = 3

add       -> 13
substract -> 7
multiply  -> 30
divide    -> 3.333333   (a Rat, exactly 10/3)

divide returns an exact Rat, which is the right answer and not what most calculators give you.

Note the spelling: the method is substract, without the first t. .subtract is a method-not-found on both engines.

Named arguments only #

use Calculator;

my $r = try Calculator.new(10, 3);
say 'positional arguments : ', $! ?? 'refused' !! 'accepted';
say 'named arguments      : ', Calculator.new(x => 10, y => 3).add;
say '';
my $n = try Calculator.new(x => 10);
say 'a missing y          : ', $! ?? 'refused' !! 'accepted';

positional arguments : refused
named arguments      : 13

a missing y          : refused

Both attributes are is required, so the constructor tells you what is missing.

The one thing to know #

The constructor, not the methods, decides what arithmetic you are allowed to do: it demands x > y > 0.

use Calculator;

sub attempt($label, &c) {
    my $r = try c();
    say sprintf('%-22s %s', $label, $! ?? 'refused' !! 'ok -> ' ~ $r);
}

attempt 'new(x=>10, y=>3).add',  { Calculator.new(x => 10, y => 3).add };
attempt 'new(x=>3,  y=>10).add', { Calculator.new(x => 3,  y => 10).add };
attempt 'new(x=>5,  y=>5).add',  { Calculator.new(x => 5,  y => 5).add };
attempt 'new(x=>5,  y=>0).add',  { Calculator.new(x => 5,  y => 0).add };
attempt 'new(x=>5,  y=>-2).add', { Calculator.new(x => 5,  y => -2).add };

new(x=>10, y=>3).add   ok -> 13
new(x=>3,  y=>10).add  refused
new(x=>5,  y=>5).add   refused
new(x=>5,  y=>0).add   refused
new(x=>5,  y=>-2).add  refused

This is a Calculator that cannot compute 3 + 10, cannot compute 5 − 5, and cannot touch zero or any negative number. The refusal happens at new, before you have named an operation — so a program that only ever wanted multiply still dies because its operands are in the wrong order, with a message about a relation that has nothing to do with multiplication.

Roughly the only genuine two-number sum this class can express is one where the first number is strictly the larger and both are positive.

Where the two engines differ #

On whether the declared attribute type is enforced at all.

has Int $.x is required where * > 0 carries both a type and a constraint. Rakudo applies both, so Calculator.new(x => 2.5, y => 1) and Calculator.new(x => '7', y => '3') are refused. Raku++ applies only the where, so the same two calls build an object and .add returns 3.5 and 10 respectively.

Code that passes a Rat or a numeric string therefore works on one engine and is refused on the other — and the one that accepts it is the one giving you an Int-declared attribute holding a Str.

The git:// source URL in the metadata uses a protocol GitHub stopped serving.