Powershell equivalent to F# Seq.forall

Question

I've written this (which works):

function ForAll {
    BEGIN {
        $allTrue = $true
    }
    PROCESS {
        if ($_ -lt 1) { $allTrue = $false }  
    }
    END {
        $allTrue
    }
}

$aList = (0..4)
$bList = (1..4)

$aList | ForAll # returns false
$bList | ForAll # returns true

But what I want to do is replace the ($_ -lt 1) with a function called something like $predicate that I pass into the ForAll function. I can't seem to get this to work. Any ideas?

Answer 1

Have a look here:

http://stackoverflow.com/questions/1094650/is-there-a-function-pointer-or-array-of-functions-in-powershell

Answer 2

Use [scriptblock], imho it is much easier than using functions here. That's the task why scriptblocks were invented.

function ForAll([scriptblock]$predicate) {

    BEGIN {
        $allTrue = $true
    }
    PROCESS {
        if (!(& $predicate $_)) { $allTrue = $false }  
    }
    END {
        $allTrue
    }
}

$aList = (0..4)
$bList = (1..4)

$aList | ForAll {$args[0] -le -10 } # returns false
$bList | ForAll {$args[0] -le 10 } # returns true

$args[0] denotes the first argument passed to the scriptblock - in this case it is $_.

Answer 3

If you're on PowerShell 2.0, you can use param with a scriptblock to declare parameters e.g.:

function ForAll {
    param(
        [Parameter(Position=0,Mandatory=$true)]
        [scriptblock]
        $Expression,

        [Parameter(Position=1,Mandatory=$true,ValueFromPipeline=$true)]
        [psobject]
        $InputObject
    ) 

    Begin { $allTrue = $true } 

    Process { 
        foreach ($obj in $InputObject) {
            if (!(&$Expression $obj)) { $allTrue = $false }
        }
    } 

    End { $allTrue } 
} 

$aList = (0..4) 
$bList = (1..4) 

ForAll {param($val) $val -gt 0} (0..4) # returns false 

$aList | ForAll {param($val) $val -gt 0} # returns false 
$bList | ForAll {param($val) $val -gt 0} # returns true 
$aList | ForAll {param($val) $val -ge 0 -and $val -le 4} # returns true