function map([scriptblock]$map, [Collections.IEnumerable]$x, $y) { $x.ForEach({& $map $_ $y}) }

# Two parameters
map { param($x, $y) $x + $y } @(1,2,3) 10

# Anonymous function as a value
$squareIt = { param($x) $x + $x }
map $squareIt @(1,2,3)

# One parameter
map { param($x) [math]::Pow($x,2) } @(1,2,3)

# Strings
map { param($x,$y) ' ' * ($y - $x.Length) + $x } (echo bob chris jack) 12


function fold([scriptblock]$fold, [Collections.IEnumerable]$x, $a) {
    $x.ForEach({
        $a = & $fold $a $_
    })
    return $a
}

$sum = { param($a,$x) $a + $x }

# Basic aggregation
fold $sum @(1,2,3)

# With initializer
fold { param($a,$x) $a + $x } @(1,2,3) 1

# Combining functions
fold $sum (map $squareIt @(1,2,3))