From dacc1aa41699ee6c8f4c49ef6061c95ea5e70017 Mon Sep 17 00:00:00 2001
From: Ian Lynagh <igloo@earth.li>
Date: Fri, 28 Nov 2008 19:17:06 +0000
Subject: [PATCH] Teach runghc about --help; fixes trac #2757

---
 docs/users_guide/runghc.xml |    7 +++---
 utils/runghc/runghc.hs      |   51 ++++++++++++++++++++++++++++---------------
 2 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/docs/users_guide/runghc.xml b/docs/users_guide/runghc.xml
index 4a6640c..ec55a43 100644
--- a/docs/users_guide/runghc.xml
+++ b/docs/users_guide/runghc.xml
@@ -13,16 +13,17 @@
 <screen>
 runghc [runghc flags] [GHC flags] module [program args]
 </screen>
-    <para>The only runghc flag currently is
+    <para>The runghc flags are
     <literal>-f /path/to/ghc</literal>,
-    which tells runghc which GHC to use to run the program. If it is
+    which tells runghc which GHC to use to run the program,
+    and <literal>--help</literal>, which prints usage information. If it is
     not given then runghc will search for GHC in the directories in the
     system search path.</para>
 
     <para>runghc will try to work out where the boundaries between
     <literal>[runghc flags]</literal> and
     <literal>[GHC flags]</literal>, and
-    <literal>[GHC flags]</literal> and
+    <literal>[program args]</literal> and
     <literal>module</literal> are, but you can use a
     <literal>--</literal> flag if it doesn't get it right. For example,
     <literal>runghc -- -fglasgow-exts Foo</literal> means runghc
diff --git a/utils/runghc/runghc.hs b/utils/runghc/runghc.hs
index 5baaeff..bfdcc96 100644
--- a/utils/runghc/runghc.hs
+++ b/utils/runghc/runghc.hs
@@ -25,6 +25,7 @@ module Main (main) where
 import Control.Exception
 import Data.Char
 import Data.List
+import Data.Monoid
 import System.Cmd
 import System.Directory
 import System.Environment
@@ -41,9 +42,10 @@ import Foreign.C.String
 main :: IO ()
 main = do
     args <- getArgs
-    case getGhcLoc args of
-        (Just ghc, args') -> doIt ghc args'
-        (Nothing, args') -> do
+    case parseRunGhcFlags args of
+        (Help, _) -> printUsage
+        (RunGhcFlags (Just ghc), args') -> doIt ghc args'
+        (RunGhcFlags Nothing, args') -> do
             mbPath <- getExecPath
             case mbPath of
                 Nothing  -> dieProg ("cannot find ghc")
@@ -51,20 +53,35 @@ main = do
                     let ghc = takeDirectory (normalise path) </> "ghc"
                     in doIt ghc args'
 
-getGhcLoc :: [String] -> (Maybe FilePath, [String])
-getGhcLoc args = case args of
-                 "-f" : ghc : args' -> f ghc args'
-                 ('-' : 'f' : ghc) : args' -> f ghc args'
-                 -- If you need the first GHC flag to be a -f flag then
-                 -- you can pass -- first
-                 "--" : args' -> (Nothing, args')
-                 _            -> (Nothing, args)
-    where f ghc args' = -- If there is another -f flag later on then
-                        -- that overrules the one that we've already
-                        -- found
-                        case getGhcLoc args' of
-                        (Nothing, _) -> (Just ghc, args')
-                        success -> success
+data RunGhcFlags = RunGhcFlags (Maybe FilePath) -- GHC location
+                 | Help -- Print help text
+
+instance Monoid RunGhcFlags where
+    mempty = RunGhcFlags Nothing
+    Help `mappend` _ = Help
+    _ `mappend` Help = Help
+    RunGhcFlags _ `mappend` right@(RunGhcFlags (Just _)) = right
+    left@(RunGhcFlags _) `mappend` RunGhcFlags Nothing = left
+
+parseRunGhcFlags :: [String] -> (RunGhcFlags, [String])
+parseRunGhcFlags = f mempty
+    where f flags ("-f" : ghc : args)
+              = f (flags `mappend` RunGhcFlags (Just ghc)) args
+          f flags (('-' : 'f' : ghc) : args)
+              = f (flags `mappend` RunGhcFlags (Just ghc)) args
+          f flags ("--help" : args) = f (flags `mappend` Help) args
+          -- If you need the first GHC flag to be a -f flag then
+          -- you can pass -- first
+          f flags ("--" : args) = (flags, args)
+          f flags         args  = (flags, args)
+
+printUsage :: IO ()
+printUsage = do
+    putStrLn "Usage: runghc [runghc flags] [GHC flags] module [program args]"
+    putStrLn ""
+    putStrLn "The runghc flags are"
+    putStrLn "    -f /path/to/ghc       Tell runghc where GHC is"
+    putStrLn "    --help                Print this usage information"
 
 doIt :: String -> [String] -> IO ()
 doIt ghc args = do
-- 
1.7.10.4