Adding await keyword (Fixes #181)

Author: James Brundage

Transpilers/Keywords/Await.psx.ps1

@@ -0,0 +1,76 @@
+<#
+.SYNOPSIS
+    awaits asynchronous operations
+.DESCRIPTION
+    awaits the result of a task.
+.EXAMPLE
+    .>PipeScript -ScriptBlock {
+        await $Websocket.SendAsync($SendSegment, 'Binary', $true, [Threading.CancellationToken]::new($false))
+    }
+.EXAMPLE
+    .>PipeScript -ScriptBlock {
+        $receiveResult = await $Websocket.ReceiveAsync($receiveSegment, [Threading.CancellationToken]::new($false))
+    }
+#>
+[ValidateScript({
+    $CommandAst = $_
+    $CommandAst.CommandElements -and $CommandAst.CommandElements[0].Value -eq 'await'
+})]
+param(
+[Parameter(Mandatory,ValueFromPipeline)]
+[Management.Automation.Language.CommandAST]
+$CommandAst
+)
+
+process {
+    if ($CommandAst.CommandElements.Count -lt 2) {
+        Write-Error "await what?"
+        return
+    }
+
+    if ($CommandAst.CommandElements[0].Value -ne 'await') {
+        Write-Error "not await"
+        return
+    }
+
+    if ($CommandAst.CommandElements[1] -isnot [Management.Automation.Language.InvokeMemberExpressionAst]) {
+        Write-Error "await must be followed by an invocation expression"
+        return
+    }
+
+    # Note: This is one of those cases where version targeting might be handy.
+    # older versions of PowerShell (I believe -lt 4.0) will not handle task returns correctly without help.
+
+    [Timespan]$awaitTimeout = '00:00:10'
+    [Timespan]$awaitSleep   = 7
+
+
+
+    $newScript = @(
+        '[DateTime]$awaitTimeout = [DateTime]::Now + "' + "$awaitTimeout" + '"'
+        '[TimeSpan]$awaitSleep   = "' + "$awaitSleep" + '"'
+        '$awaitTask = ' + "$($commandAst.CommandElements[1].Extent.ToString())"
+{
+while (!$awaitTask.IsCompleted -and [DateTime]::Now -lt $awaitTimeout) {
+    Start-Sleep -Milliseconds $awaitSleep.TotalMilliseconds
+}
+if ($awaitTask.IsCompleted -and $null -ne $awaitTask.Result) {
+    $awaitTask.Result
+}
+elseif ($awaitTask.IsCompleted -and $awaitTask.Exception) {
+    if ($awaitTask.Exception.InnerExceptions) {
+        $awaitTask.Exception.InnerExceptions
+    } else {
+        $awaitTask.Exception
+    }
+}
+}
+
+    ) -join [Environment]::NewLine
+
+    if ($CommandAst.IsAssigned) {
+        $newScript = "`$($newScript)"
+    }
+
+    [ScriptBlock]::create($newScript)
+}

Transpilers/Keywords/Await.tests.ps1

@@ -0,0 +1,9 @@
+describe Await {
+    it 'Lets us wait for asynchronous results' {
+        Invoke-PipeScript -ScriptBlock {
+            $webRequest    = new Net.HttpWebRequest "https://api.github.com/repos/StartAutomating/PipeScript"
+            $awaitedResult = await $webRequest.GetResponseAsync()
+            $awaitedResult | Should -not -be $null
+        }
+    }
+}