Functional programming with Powershell

Higher Order Functions.ps1

function Convert-ByFilter($values, $predicate) {
    return $values | where { & $predicate $_ }
}

Describe "Higher Order Functions" {
    $values = @(1, 2, 3, 4)
 
    It "Should filter even" {
        $evenPredicate = { param($value) return $value % 2 -eq 0 }
        $even = Convert-ByFilter $values $evenPredicate
        $even.Length | Should Be 2
        $even[0] | Should Be 2
        $even[1] | Should Be 4
         
    }
 
    It "Should filter odd" {
        $oddPredicate = { param($value) return $value % 2 -eq 1 }
        $odd = Convert-ByFilter $values $oddPredicate
        $odd.Length | Should Be 2
        $odd[0] | Should Be 1
        $odd[1] | Should Be 3
    }
}