Let render take a string to specify the render type

This seems cleaner than a boolean parameter.

Author: tarleb

README.md

@@ -53,7 +53,7 @@ Documentation
 
 #### render
 
-`render (doc[, colwidth[, ansi]])`
+`render (doc[, colwidth[, style]])`
 
 Render the `Doc` using the given column width.
 
@@ -65,9 +65,9 @@ Parameters:
 `colwidth`
 :   Maximum number of characters per line
 
-`ansi`
-:   Whether to generate plain or ANSI terminal output. Defaults to
-    `false`.  (boolean)
+`style`
+:   Whether to generate 'plain' or 'ANSI' terminal output. Must be
+    either `'plain'` or `'ansi'`. Defaults to `'plain'`. (string)
 
 ### Doc construction
 

src/HsLua/Module/DocLayout.hs

@@ -268,15 +268,22 @@ render = defun "render"
            "Maximum number of characters per line.\n" <>
            "A value of `nil`, the default, means that the text " <>
            "is not reflown.")
-  <#> opt (boolParam "ansi" $
+  <#> opt (parameter peekRenderStyle "string" "style" $
            "Whether to generate plain text or ANSI terminal output.\n" <>
-           "Defaults to `false`.")
+           "Must be either `'plain'` or `'ansi'`.\n" <>
+           "Defaults to `'plain'`.")
   =#> functionResult pushText "string" "rendered doc"
   #? T.unlines
      [ "Render a [[Doc]]. The text is reflowed on breakable spaces to"
      , "match the given line length. Text is not reflowed if the line"
      , "line length parameter is omitted or nil."
      ]
+ where
+   peekRenderStyle idx = peekByteString idx >>= \case
+     "ansi"  -> pure True
+     "ANSI"  -> pure True
+     "plain" -> pure False
+     style   -> failPeek $ "Unknown rendering style: " <> style
 
 --
 -- Querying