functional.psm1
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## # enums # enum MergeStrategy { Add Override Fail } enum ParamStyle { Implicit Explicit Infer } enum Direction { Left Right } ## # module variables # $Strategies = @{ Add = { Param($a, $b) return $a + $b } Override = { Param($a, $b) return $b } Fail = { Param($a, $b) throw "Cannot merge type '$($a.GetType())' and '$($b.GetType())'" } } ## # helper functions # # don't use `-is [PSCustomObject]` # https://github.com/PowerShell/PowerShell/issues/9557 function isPsCustomObject($v) { $v.PSTypeNames -contains 'System.Management.Automation.PSCustomObject' } # recursively test $a and $b for deep equality function recursiveEquality($a, $b) { if ($a -is [array] -and $b -is [array]) { Write-Debug "recursively test arrays '$a' '$b'" if ($a.Count -ne $b.Count) { return $false } $inequalIndexes = 0..($a.Count - 1) | ? { -not (recursiveEquality $a[$_] $b[$_]) } return $inequalIndexes.Count -eq 0 } if ($a -is [hashtable] -and $b -is [hashtable]) { Write-Debug "recursively test hashtable '$a' '$b'" $inequalKeys = $a.Keys + $b.Keys ` | Sort-Object -Unique ` | ? { -not (recursiveEquality $a[$_] $b[$_]) } return $inequalKeys.Count -eq 0 } if ((isPsCustomObject $a) -and (isPsCustomObject $b)) { Write-Debug "a is pscustomobject: $($a -is [psobject])" Write-Debug "recursively test objects '$a' '$b'" $inequalKeys = $a.psobject.Properties + $b.psobject.Properties ` | % Name ` | Sort-Object -Unique ` | ? { -not (recursiveEquality $a.$_ $b.$_) } return $inequalKeys.Count -eq 0 } Write-Debug "test leaves '$a' '$b'" return $a.GetType() -eq $b.GetType() -and $a -eq $b } # merge `$a` and `$b` recursively. If `$a` and `$b` cannot be merged, # pass `$a` and `$b` to `$strategy` to resolve the conflict. function recursiveMerge($a, $b, [scriptblock]$strategy) { if ($null -eq $a) { Write-Debug "new assignment '$b'" return $b } if ($a -eq $b -or $null -eq $b) { Write-Debug "existing assignment '$a'" return $a } if ($a -is [array] -and $b -is [array]) { Write-Debug "merge arrays '$a' '$b'" return $a + $b | Sort-Object -Unique } if ($a -is [hashtable] -and $b -is [hashtable]) { Write-Debug "merge hashtable '$a' '$b'" $merged = @{ } $a.Keys + $b.Keys ` | Sort-Object -Unique ` | % { $merged[$_] = recursiveMerge $a[$_] $b[$_] $strategy } return $merged } if ((isPsCustomObject $a) -and (isPsCustomObject $b)) { Write-Debug "a is pscustomobject: $($a -is [psobject])" Write-Debug "merge objects '$a' '$b'" $merged = @{ } $a.psobject.Properties + $b.psobject.Properties ` | % Name ` | Sort-Object -Unique ` | % { $merged[$_] = recursiveMerge $a.$_ $b.$_ $strategy } return [PSCustomObject]$merged } Write-Debug "resolve conflict '$a' '$b'" return &$strategy $a $b } ## # exported functions # <# .SYNOPSIS Merges all the input objects using the specified conflict resolution strategy .OUTPUTS The merged value #> function Merge-Object { Param( # The objects to merge [Parameter(Mandatory, ValueFromPipeline, ParameterSetName = "Named")] [Parameter(Mandatory, ValueFromPipeline, ParameterSetName = "Explicit")] [ValidateNotNullOrEmpty()] [object[]] $Object, # The conflict resolution strategy [Parameter(Mandatory, ParameterSetName = "Named")] [ValidateNotNullOrEmpty()] [MergeStrategy] $Strategy, # Resolves merge conflicts between two objects [Parameter(Mandatory, ParameterSetName = "Explicit")] [ValidateScript( { $_.Ast.ParamBlock.Parameters.Count -in (0, 2) } )] [scriptblock] $Resolver ) if (-not $Resolver) { $Resolver = $Strategies["$Strategy"] } # we need to use explicit params because implicit params are invoked in a closure, # whereas we need our scriptblock to have access to $Strategies $reducer = { Param($a, $b); recursiveMerge $a $b $Resolver } $input | Reduce-Object $reducer } function Merge-ScriptBlock { [OutputType([scriptblock])] Param( [Parameter(Mandatory, ValueFromPipeline)] [ValidateScript( { $_ | % { $_.Ast.ParamBlock.Parameters.Count -eq 1 } | Test-All } )] [scriptblock[]] $ScriptBlock ) $reducer = { Param($a, $b) { Param($arg) &$a (&$b $arg) }.GetNewClosure() } $input | Reduce-Object $reducer } <# .SYNOPSIS Reduces a pipeline with the given reducer function .OUTPUTS The accumulated value .NOTES Reduce is an unapproved Verb, but none of the approved verbs accurately describe what we're doing, so we are conforming to Verb-Noun convention like other *-Object cmdlets instead #> function Reduce-Object { [Diagnostics.CodeAnalysis.SuppressMessageAttribute("PSUseApprovedVerbs", "")] Param( # The function applied to the accumulator and each element of the input [Parameter(Mandatory)] [ValidateScript( { $_.Ast.ParamBlock.Parameters.Count -in (0, 2) } )] [scriptblock] $Reducer, # The objects to merge [Parameter(Mandatory, ValueFromPipeline)] [ValidateNotNullOrEmpty()] [object[]] $Object, [ParamStyle] $ParamStyle = "Infer", [Direction] $Direction = "Right" ) # deduce and validate scriptblock invokation style $paramCount = $Reducer.Ast.ParamBlock.Parameters.Count $implicit = $ParamStyle -ne "Explicit" -and $paramCount -eq 0 $explicit = $ParamStyle -ne "Implicit" -and $paramCount -eq 2 if (-not ($implicit -or $explicit)) { throw "Could not reconcile Reducer parameter count '$paramCount' with param declaration style '$ParamStyle'" } # normalize input if ($Direction -eq [Direction]::Left) { [array]::Reverse($input) } # invoke the reducer $accum = $input | Select -First 1 if ($implicit) { foreach ($object in $input | Select -Skip 1) { # invoke in scriptblock to minimize exposure of local variables $safelyScoped = { Param($a, $b, [scriptblock]$reducer) . $reducer.GetNewClosure() } $accum = &$safelyScoped $accum $object $Reducer } } if ($explicit) { foreach ($object in $input | Select -Skip 1) { $accum = &$Reducer $accum $object } } return $accum } <# .SYNOPSIS Returns true if all elements in the pipeline are truthy #> function Test-All { [OutputType([boolean])] Param() foreach ($e in $input) { if (-not $e) { return $false } } return $true } <# .SYNOPSIS Returns true if any of the elements in the pipeline are truthy #> function Test-Any { [OutputType([boolean])] Param() foreach ($e in $input) { if ($e) { return $true } } return $false } <# .SYNOPSIS Returns true if all elements in the pipeline are equival .DESCRIPTION Compares each element in the pipeline to the first pipeline element using a deep/recursive equality check of the properties and items #> function Test-Equality { [OutputType([boolean])] Param( # The objects to compare for equality [Parameter(Mandatory, ValueFromPipeline)] [ValidateNotNullOrEmpty()] [object[]] $Object ) $head = $input | Select -First 1 $input | Select -Skip 1 | % { recursiveEquality $head $_ } | Test-All } ## # aliases # New-Alias -Name "merge" -Value Merge-Object New-Alias -Name "reduce" -Value Reduce-Object New-Alias -Name "forall" -Value Test-All New-Alias -Name "exists" -Value Test-Any |