Task: Currying






PHP: <?php

function curry($callable)
{
    if (_number_of_required_params($callable) === 0) {
        return _make_function($callable);
    }
    if (_number_of_required_params($callable) === 1) {
        return _curry_array_args($callable, _rest(func_get_args()));
    }
    return _curry_array_args($callable, _rest(func_get_args()));
}

function _curry_array_args($callable, $args, $left = true)
{
    return function () use ($callable, $args, $left) {
        if (_is_fullfilled($callable, $args)) {
            return _execute($callable, $args, $left);
        }
        $newArgs = array_merge($args, func_get_args());
        if (_is_fullfilled($callable, $newArgs)) {
            return _execute($callable, $newArgs, $left);
        }
        return _curry_array_args($callable, $newArgs, $left);
    };
}

function _number_of_required_params($callable)
{
    if (is_array($callable)) {
        $refl = new \ReflectionClass($callable[0]);
        $method = $refl->getMethod($callable[1]);
        return $method->getNumberOfRequiredParameters();
    }
    $refl = new \ReflectionFunction($callable);
    return $refl->getNumberOfRequiredParameters();
}

function _make_function($callable)
{
    if (is_array($callable))
        return function() use($callable) {
            return call_user_func_array($callable, func_get_args());
        };
    return $callable;
}

function _execute($callable, $args, $left)
{
    if (! $left) {
        $args = array_reverse($args);
    }
    $placeholders = _placeholder_positions($args);
    if (0 < count($placeholders)) {
        $n = _number_of_required_params($callable);
        if ($n <= _last($placeholders[count($placeholders) - 1])) {
            throw new \Exception('Argument Placeholder found on unexpected position!');
        }
        foreach ($placeholders as $i) {
            $args[$i] = $args[$n];
            array_splice($args, $n, 1);
        }
    }
    return call_user_func_array($callable, $args);
}

function _placeholder_positions($args)
{
    return array_keys(array_filter($args, '_is_placeholder'));
}

function _is_fullfilled($callable, $args)
{
    $args = array_filter($args, function($arg) {
        return ! _is_placeholder($arg);
    });
    return count($args) >= _number_of_required_params($callable);
}

function _is_placeholder($arg)
{
    return $arg instanceof Placeholder;
}

function _rest(array $args)
{
    return array_slice($args, 1);
}

function product($a, $b)
{
    return $a * $b;
}

echo json_encode(array_map(curry('product', 7), [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]));



VB: Option Explicit On
Option Infer On
Option Strict On

Module Currying
    
    Function Curry(Of T1, TResult)(func As Func(Of T1, TResult)) As Func(Of T1, TResult)
        
        Return Function(a) func(a)
    End Function

    Function Curry(Of T1, T2, TResult)(func As Func(Of T1, T2, TResult)) As Func(Of T1, Func(Of T2, TResult))
        Return Function(a) Function(b) func(a, b)
    End Function

    Function Curry(Of T1, T2, T3, TResult)(func As Func(Of T1, T2, T3, TResult)) As Func(Of T1, Func(Of T2, Func(Of T3, TResult)))
        Return Function(a) Function(b) Function(c) func(a, b, c)
    End Function

    
End Module