From 512cacb051d7e7c72192462fd19dada8342204e2 Mon Sep 17 00:00:00 2001
From: Jason Dusek <jason.dusek@gmail.com>
Date: Sun, 17 Mar 2013 00:23:30 +0000
Subject: [PATCH] Provide a safe/defaulting element lookup.

---
 hs/Language/Bash/PrettyPrinter.hs | 4 ++++
 hs/Language/Bash/Syntax.hs        | 3 +++
 hs/bash.cabal                     | 2 +-
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/hs/Language/Bash/PrettyPrinter.hs b/hs/Language/Bash/PrettyPrinter.hs
index 2c2c845..8091eca 100644
--- a/hs/Language/Bash/PrettyPrinter.hs
+++ b/hs/Language/Bash/PrettyPrinter.hs
@@ -72,6 +72,8 @@ instance (Annotation t) => PP (Expression t) where
   pp (ARGVLength)            =  word "$#"
   pp (Elements ident)        =  (word . quote . braces)
                                 (bytes ident `append` "[@]")
+  pp (ElementsSafe ident)    =  (word . quote . braces_)
+                                (bytes ident `append` "[@]")
   pp (Keys ident)            =  (word . quote . braces)
                                 ('!' `cons` bytes ident `append` "[@]")
   pp (Length ident)          =  (word . quote . braces)
@@ -188,6 +190,8 @@ braces b                     =  "${" `append` b `snoc` '}'
 
 braces0 b                    =  "${" `append` b `append` ":-}"
 
+braces_ b                    =  concat ["${", b, ":+${", b, "}}"]
+
 brackets b                   =  cons '[' b `snoc` ']'
 
 identpart (VarSpecial special) = (drop 1 . bytes) special
diff --git a/hs/Language/Bash/Syntax.hs b/hs/Language/Bash/Syntax.hs
index 75b84a0..bc19d7b 100644
--- a/hs/Language/Bash/Syntax.hs
+++ b/hs/Language/Bash/Syntax.hs
@@ -157,6 +157,7 @@ data Expression t            =  Literal Esc.Bash
                              |  ARGVElements
                              |  ARGVLength
                              |  Elements Identifier
+                             |  ElementsSafe Identifier
                              |  Keys Identifier
                              |  Length VarName
                              |  Trim Trim VarName (Expression t)
@@ -186,6 +187,7 @@ instance Functor Expression where
     ARGVElements            ->  ARGVElements
     ARGVLength              ->  ARGVLength
     Elements ident          ->  Elements ident
+    ElementsSafe ident      ->  Elements ident
     Keys ident              ->  Keys ident
     Length ident            ->  Length ident
     Trim trim v expr        ->  Trim trim v (fmap f expr)
@@ -208,6 +210,7 @@ instance Foldable Expression where
     ARGVElements            ->  mempty
     ARGVLength              ->  mempty
     Elements _              ->  mempty
+    ElementsSafe _          ->  mempty
     Keys _                  ->  mempty
     Length _                ->  mempty
     Trim _ _ expr           ->  foldMap f expr
diff --git a/hs/bash.cabal b/hs/bash.cabal
index da6e8ad..20e8f1e 100644
--- a/hs/bash.cabal
+++ b/hs/bash.cabal
@@ -1,5 +1,5 @@
 name                          : bash
-version                       : 0.1.6
+version                       : 0.1.8
 category                      : Language
 license                       : BSD3
 license-file                  : LICENSE