Promises

use v6;

class Promise {
    enum STATE <PENDING FULFILLED REJECTED>;

    has STATE $!state;
    has %!do-actions;

    method state {
        $!state;
    }

    method fulfill($val!) {
        if $!state != STATE::FULFILLED {
            $!state = STATE::FULFILLED;
            %!do-actions<fulfill> = $val;
        }
    }
    method reject($reason!) {
        if $!state != STATE::REJECTED {
            $!state = STATE::REJECTED;
            %!do-actions<reject> = $reason;
        }
    }

    method then($on-fulfill?, $on-reject?) {
        if $!state == STATE::PENDING {
            %!do-actions<fulfill>.push: { $on-fulfill } if $on-fulfill;
            %!do-actions<reject>.push: { $on-reject } if $on-reject;
        } elsif %!state == STATE::REJECTED {
            %!do-actions<reject>.map: { $^x.() };
        } else {
            %!do-actions<fulfill>.map: { $^x.() };
        }
        return self;
    }

}