fancier prompts for ghci

[jsnx]

It'd be nice to put newlines in a GHCi prompt using standard escape sequences.

It is really unnecessary to support anything more than %s as a formatting directive.

[jsnx]

I've integrated this with GHC 6.8.3 sources. There's not much to it.

compiler/ghci/InteractiveUI.hs

@@ -1447 +1447 @@
 setPrompt value = do
   st <- getGHCiState
   if null value
-      then io $ hPutStrLn stderr $ "syntax: :set prompt <prompt>, currently \"" ++ prompt st ++ "\""
-      else setGHCiState st{ prompt = remQuotes value }
+      then io $ hPutStrLn stderr $
+        "syntax: :set prompt <prompt>, currently \"" ++ prompt st ++ "\""
+      else setGHCiState st{ prompt = read . handleQuotes $ value }
   where
-     remQuotes ('\"':xs) | not (null xs) && last xs == '\"' = init xs
-     remQuotes x = x
+     -- the prompt can be input with quote marks and string escaping, or
+     -- with plain character escaping.
+     handleQuotes s | length s > 2 && last s == '"' && head s == '"' = s
+                    | otherwise = wrap . escapeQuotes $ s
+     wrap = ("\"" ++) . (++ "\"")
+     escapeQuotes ('\\':'"':r) = '\\' : '"' : escapeQuotes r
+     escapeQuotes ('"':r) = '\\' : '"' : escapeQuotes r
+     escapeQuotes (c:r) = c : escapeQuotes r
+     escapeQuotes [ ] = [ ]
 
 setOptions wds =
    do -- first, deal with the GHCi opts (+s, +t, etc.)

With quotes, it uses string escapes and retains spaces:

Prelude> :set prompt "{-  %s\n -} "
{-  Prelude
 -}  

Without quotes, it uses only character escapes:

Prelude> :set prompt {-\SP\SP%s\n\SP-}\SP
{-  Prelude
 -}  

[jsnx]

this is the diff mentioned in comment 3 (turns out the diff is not extractable in this version of trac)

[igloo]

Thanks for the patch! I've applied a slightly different version: Prompt strings starting with " are treated as Haskell strings; otherwise they are treated as literal strings.

[jsnx]

Replying to igloo:

Thanks for the patch! I've applied a slightly different version: Prompt strings starting with " are treated as Haskell strings; otherwise they are treated as literal strings.

Is this going to be in 6.12? I've noticed it's not included in 6.10.

[igloo]

Yes, this patch is only in the HEAD (which will become 6.12):

Fri Oct 31 14:52:27 GMT 2008  Ian Lynagh <igloo@earth.li>
  * :set prompt now understand Haskell String syntax; trace #2652