Adding until keyword and tests (#146)

Author: James Brundage

Transpilers/Keywords/Until.psx.ps1

@@ -0,0 +1,107 @@
+<#
+.SYNOPSIS
+    until keyword
+.DESCRIPTION
+    The until keyword simplifies event loops.
+
+    until will always run at least once, and will run until a condition is true.
+.NOTES
+    until will become a ```do {} while ()``` statement in PowerShell.
+.EXAMPLE
+    {
+        $x = 0
+        until ($x == 10) {
+            $x            
+            $x++
+        }        
+    } |.>PipeScript
+.EXAMPLE
+    {
+        until "00:00:05" {
+            [DateTime]::Now
+            Start-Sleep -Milliseconds 500
+        } 
+    } | .>PipeScript
+.EXAMPLE
+    Invoke-PipeScript {
+        $tries = 3
+        until (-not $tries) {
+            "$tries tries left"
+            $tries--            
+        }
+    }
+#>
+[ValidateScript({
+    $commandAst = $_    
+    return ($commandAst -and 
+        $CommandAst.CommandElements[0].Value -eq 'until' -or
+        (
+            $commandAst.CommandElements.Count -ge 2 -and 
+            $commandAst.CommandElements[0].Value -like ':*' -and
+            $commandAst.CommandElements[1].Value -eq 'until'
+        )
+    )
+})]
+param(
+[Parameter(Mandatory,ValueFromPipeline,ParameterSetName='CommandAst')]
+[Management.Automation.Language.CommandAst]
+$CommandAst
+)
+
+process {
+    $CommandName, $CommandArgs = $commandAst.CommandElements
+    if ($commandName -like ':*') {
+        $null, $firstArg, $secondArg = $CommandAst.ArgumentList
+    } else {
+        $firstArg, $secondArg = $CommandAst.ArgumentList
+    }
+    
+
+    # If the first arg is a command expression, it becomes do {} while ($firstArg)
+    if (-not $firstArg -or $firstArg.GetType().Name -notin 
+        'ParenExpressionAst', 'ScriptBlockExpressionAst',
+        'VariableExpressionAst','MemberExpressionAst','ExpandableStringExpressionAst') {
+        Write-Error "Until must be followed by a Variable, Member, String, or Parenthesis Expression"
+        return
+    }
+
+    if ($secondArg -isnot [Management.Automation.Language.ScriptBlockExpressionAst]) {
+        Write-Error "Until must be followed by a condition and a ScriptBlock"
+        return
+    }
+
+    $condition = $firstArg
+    if ($firstArg.GetType().Name -eq 'ParenExpressionAst' -and 
+        $firstArg.Pipeline.PipelineElements.Count -eq 1 -and 
+        $firstArg.Pipeline.PipelineElements[0].Expression -and 
+        $firstArg.Pipeline.PipelineElements[0].Expression.GetType().Name -in 
+        'VariableExpressionAst','MemberExpressionAst','ExpandableStringExpressionAst') {
+        $condition = $firstArg.Pipeline.PipelineElements[0].Expression
+    }
+    elseif ($firstArg.GetType().Name -eq 'ScriptBlockExpressionAst') {
+        $condition = $firstArg -replace '^\{' -replace '\}$'
+    }
+
+    $conditionScript = [ScriptBlock]::Create($condition)
+    $LoopScript = $secondArg.Extent.ToString() -replace '^\{' -replace '\}$'    
+
+    $secondArgScriptBlock = [ScriptBlock]::Create($LoopScript)
+    
+    $conditionScript = $conditionScript      | .>Pipescript
+    $untilTranspiled = $secondArgScriptBlock | .>Pipescript
+    $conditionScript = 
+        if ($conditionScript -match '^\(') {
+            "(-not $conditionScript)"
+        } else {
+            "(-not ($conditionScript))"
+        }
+    
+    
+    $newScript = @"
+$(if ($CommandName -like ':*') { "$CommandName "})do {
+$untilTranspiled
+} while $conditionScript
+"@
+    
+    [ScriptBlock]::Create($newScript)
+}

Transpilers/Keywords/Until.tests.ps1

@@ -0,0 +1,23 @@
+describe "'until' keyword" {    
+    it "Is a loop that runs until the condition is false" {
+        Invoke-PipeScript { 
+            $x = 0 
+            until ($x -ge 10) {
+                $x++
+            }
+            $x
+        } | Should -Be 10
+    }
+    it 'Can have a loop label' {
+        Invoke-PipeScript { 
+            $x = 0 
+            :thisUntil until ($x -ge 10) {
+                $x++
+                break thisUntil
+            }
+            $x
+        } | Should -Be 10
+    }
+}
+
+