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Artifact 5d16a20cc646981e2d293c6f7be4e63348305fb7351d81889f2fda3544830e7f:

  • File partial-application.ps1 — part of check-in [cb6955222c] at 2018-06-10 13:00:04 on branch trunk — A proof of concept module implementing partial application (not currying) of functions and cmdlets in powershell. This is a functional language technique often used in languages like Haskell, ML etc. (user: Oisin Grehan size: 8198)

# encoding: ascii
# api: powershell
# title: partial application
# description: A proof of concept module implementing partial application (not currying) of functions and cmdlets in powershell. This is a functional language technique often used in languages like Haskell, ML etc.
# version: 0.1
# type: function
# author: Oisin Grehan
# license: CC0
# function: Get-ParameterDictionary
# x-poshcode-id: 1687
# x-archived: 2016-11-14T09:21:34
# x-published: 2010-03-10T16:56:00
#
#
Set-StrictMode -Version 2

$commonParameters = @("Verbose",
                      "Debug",
                      "ErrorAction",
                      "WarningAction",
                      "ErrorVariable",
                      "WarningVariable",
                      "OutVariable",
                      "OutBuffer")

<#
.SYNOPSIS
    Support function for partially-applied cmdlets and functions.
#>
function Get-ParameterDictionary {
    [outputtype([Management.Automation.RuntimeDefinedParameterDictionary])]
    [cmdletbinding()]
    param(
        [validatenotnull()]
        [management.automation.commandinfo]$CommandInfo,
        [validatenotnull()]
        [management.automation.pscmdlet]$PSCmdletContext = $PSCmdlet
    )
    
    # dictionary to hold dynamic parameters
    $rdpd = new-object Management.Automation.RuntimeDefinedParameterDictionary

    try {
        # grab parameters from function
        if ($CommandInfo.parametersets.count > 1) {
            $parameters = $CommandInfo.ParameterSets[[string]$CommandInfo.DefaultParameterSet].parameters
        } else {
            $parameters = $CommandInfo.parameters.getenumerator() | % {$CommandInfo.parameters[$_.key]}
        }        
                
        $parameters | % {
            
            write-verbose "testing $($_.name)"
                                    
            # skip common parameters        
            if ($commonParameters -like $_.Name) {                                  
                
                write-verbose "skipping common parameter $($_.name)"
                
            } else {
                
                $rdp = new-object management.automation.runtimedefinedparameter
                $rdp.Name = $_.Name
                $rdp.ParameterType = $_.ParameterType
                
                # tag new parameters to match this function's parameterset
                $pa = new-object system.management.automation.parameterattribute
                $pa.ParameterSetName = $PSCmdletContext.ParameterSetName
                $rdp.Attributes.Add($pa)
                
                $rdpd.add($_.Name, $rdp)
            }
            
        }
    } catch {
    
        Write-Warning "Error getting parameter dictionary: $_"
    }
    
    # return
    $rdpd
}

<#
.SYNOPSIS
    Function that accepts a FunctionInfo or CmdletInfo reference and one or more parameters
    and returns a FunctionInfo bound to those parameter(s) and their value(s.)
.DESCRIPTION
    Function that accepts a FunctionInfo or CmdletInfo reference and one or more parameters
    and returns a FunctionInfo bound to those parameter(s) and their value(s.)
    
    Any parameters "merged" into the function are removed from the available parameters for
    future invocations. Multiple chained merge-parameter calls are permitted.
.EXAMPLE

    First, we define a simple function:
    
    function test {
        param($a, $b, $c, $d);
        "a: $a; b: $b; c:$c; d:$d"
    }
    
    Now we merge -b parameter into functioninfo with the static value of 5, returning a new
    functioninfo:
    
    ps> $x = merge-parameter (gcm test) -b 5
    
    We execute the new functioninfo with the & (call) operator, passing in the remaining 
    arguments:
    
    ps> & $x -a 2 -c 4 -d 9
    a: 2; b: 5; c: 4; d: 9
    
    Now we merge two new parameters in, -c with the value 3 and -d with 5:
    
    ps> $y = merge-parameter $x -c 3 -d 5
    
    Again we call $y with the remaining named parameter -a:
    
    ps> & $y -a 2
    a: 2; b: 5; c: 3; d: 5
.EXAMPLE

    Cmdlets can also be subject to partial application. In this case we create a new
    function with the returned functioninfo:
    
    ps> si function:get-function (merge-parameter (gcm get-command) -commandtype function)
    ps> get-function
    <lists all commands of commandtype "function">            
.PARAMETER _CommandInfo
    The FunctionInfo or CmdletInfo into which to merge (apply) parameter(s.)
    
    The parameter is named with a leading underscore character to prevent parameter
    collisions when exposing the targetted command's parameters and dynamic parameters.
.INPUTS
    FunctionInfo or CmdletInfo
.OUTPUTS
    FunctionInfo
#>
function Merge-Parameter {    
    [OutputType([Management.Automation.FunctionInfo])]
    [CmdletBinding()]
    param(
        [parameter(position=0, mandatory=$true)]
        [validatenotnull()]
        [validatescript({
            ($_ -is [management.automation.functioninfo]) -or `
            ($_ -is [management.automation.cmdletinfo])
        })]
        [management.automation.commandinfo]$_Command
    )
    
    dynamicparam {
        # strict mode compatible check for parameter
        if ((test-path variable:_command)) {
            # attach input functioninfo's parameters to self
            Get-ParameterDictionary $_Command $PSCmdlet
        }
    }

    begin {
        write-verbose "merge-parameter: begin"
        
        # copy our bound parameters, except common ones              
        $mergedParameters = new-object 'collections.generic.dictionary[string,object]' $PSBoundParameters
        
        # remove our parameters, leaving only target function/CommandInfo's args to curry in
        $mergedParameters.remove("_Command") > $null
        
        # remove common parameters
        $commonParameters | % {
            if ($mergedParameters.ContainsKey($_)) {
                $mergedParameters.Remove($_)  > $null
            }
        }
    }
    
    process {
        write-verbose "merge-parameter: process"
        
        # temporary function name
        $temp = [guid]::NewGuid()

        $target = $_Command

        # splat our fixed named parameter(s) and then splat remaining args
        $partial = {
            [cmdletbinding()]
            param()
            
            # begin dynamicparam
            dynamicparam
            {                
                $targetRdpd = Get-ParameterDictionary $target $PSCmdlet
        
                # remove fixed parameters
                $mergedParameters.keys | % {
                    $targetRdpd.remove($_) > $null
                }
                $targetRdpd
            }
            begin {
                write-verbose "i have $($mergedParameters.count) fixed parameter(s)."
                write-verbose "i have $($targetrdpd.count) remaining parameter(s)"
            }
            # end dynamicparam
            process {
                $boundParameters = $PSCmdlet.MyInvocation.BoundParameters
                
                # remove common parameters (verbose, whatif etc)
                $commonParameters | % {
                    if ($boundParameters.ContainsKey($_)) {
                        $boundParameters.Remove($_)  > $null
                    }
                }
                
                # invoke command with fixed parameters and passed parameters (all named)
                . $target @mergedParameters @boundParameters
                
                if ($args) {
                    write-warning "received $($args.count) arg(s) not part of function."
                }
            }
        }
        
        # emit function/CommandInfo
        new-item -Path function:$temp -Value $partial.GetNewClosure()
    }
    
    end {
        # cleanup
        rm function:$temp
    }    
}

new-alias papp Merge-Parameter -force

Export-ModuleMember -Alias papp -Function Merge-Parameter, Get-ParameterDictionary