[Pkg-haskell-commits] [SCM] haskell-testpack branch, master, updated. debian/1.0.2-1-4-gb0d6b36

[John Goerzen]

The following commit has been merged in the master branch:
commit ba4312e92531238ef20173970fe30419e319e672
Author: John Goerzen <jgoerzen at complete.org>
Date:   Wed Dec 1 04:52:26 2004 +0100

    Checkpointing
    
    Keywords:
    
    
    (jgoerzen at complete.org--projects/missingh--head--0.5--patch-133)

diff --git a/ChangeLog b/ChangeLog
index 1b061c4..d73b8f1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,19 @@
 # arch-tag: automatic-ChangeLog--jgoerzen at complete.org--projects/missingh--head--0.5
 #
 
+2004-11-30 21:52:26 GMT	John Goerzen <jgoerzen at complete.org>	patch-133
+
+    Summary:
+      Checkpointing
+    Revision:
+      missingh--head--0.5--patch-133
+
+
+    modified files:
+     ChangeLog libsrc/MissingH/ConfigParser.hs
+     testsrc/ConfigParser/Maintest.hs
+
+
 2004-11-30 20:57:23 GMT	John Goerzen <jgoerzen at complete.org>	patch-132
 
     Summary:
diff --git a/libsrc/MissingH/ConfigParser.hs b/libsrc/MissingH/ConfigParser.hs
index 3e7e0be..c4e5455 100644
--- a/libsrc/MissingH/ConfigParser.hs
+++ b/libsrc/MissingH/ConfigParser.hs
@@ -62,6 +62,7 @@ module MissingH.ConfigParser
      -- $usagenomonad
 
      -- ** Error Monad Usage
+     -- $usageerrormonad
 
      -- * Types
      SectionSpec, OptionSpec, ConfigParser(..),
@@ -571,7 +572,55 @@ You can transform errors into exceptions in your code by using
 
 In short, you can just put @forceEither $@ in front of every call that returns
 a 'CPResult'.  This is still a pure functional call, so it can be used outside
-of any monads.
+of the IO monads.  The exception, however, can only be caught in the IO
+monad.
+
+If you don't want to bother with 'forceEither', you can use the error monad.  It's simple and better... read on.
+-}
+
+{- $usageerrormonad
+
+The 'CPResult' type is actually defined in terms of the Error monad, which is
+itself based on the Either data type.
+
+Here's a neat example of chaining together calls to build up a 'ConfigParser'
+object:
+
+>do let cp = emptyCP
+>   cp <- add_section cp "sect1"
+>   cp <- set cp "sect1" "opt1" "foo"
+>   cp <- set cp "sect1" "opt2" "bar"
+>   options cp "sect1"
+
+The return value of this little snippet is @Right [\"opt1\", \"opt2\"]@.
+(Note to beginners: unlike the IO monad, you /can/ escape from the Error
+monad.)
+
+Although it's not obvious, there actually was error checking there.  If
+any of those calls would have generated an error, processing would have
+stopped immediately and a @Left@ value would have been returned.  Consider
+this example:
+
+>do let cp = emptyCP
+>   cp <- add_section cp "sect1"
+>   cp <- set cp "sect1" "opt1" "foo"
+>   cp <- set cp "sect2" "opt2" "bar"
+>   options cp "sect1"
+
+The return value from this is @Left ('NoSection' \"sect2\", \"set\")@.  The
+second call to 'set' failed, so the final call was skipped, and the result
+of the entire computation was considered to be an error.
+
+You can combine this with the non-monadic style to get a final, pure value
+out of it:
+
+>forceEither $ do let cp = emptyCP
+>                 cp <- add_section cp "sect1"
+>                 cp <- set cp "sect1" "opt1" "foo"
+>                 cp <- set cp "sect1" "opt2" "bar"
+>                 options cp "sect1"
+
+This returns ["opt1", "opt2"].  A quite normal value.
 
 -}
 
diff --git a/testsrc/ConfigParser/Maintest.hs b/testsrc/ConfigParser/Maintest.hs
index 634112d..655da4a 100644
--- a/testsrc/ConfigParser/Maintest.hs
+++ b/testsrc/ConfigParser/Maintest.hs
@@ -109,10 +109,35 @@ test_ex_nomonad =
        hPutStr fh "Your setting is:"
        hPutStr fh $ forceEither $ get cp "file1" "location"
 
-                 
+test_ex_errormonad = 
+    [ 
+      TestLabel "chaining1" $ TestCase $ 
+      (Right ["opt1", "opt2"]) @=? 
+       do let cp = emptyCP
+          cp <- add_section cp "sect1"
+          cp <- set cp "sect1" "opt1" "foo"
+          cp <- set cp "sect1" "opt2" "bar"
+          options cp "sect1"
+     ,TestLabel "chaining2" $ TestCase $ 
+      (Left (NoSection "sect2", "set")) @=? 
+       do let cp = emptyCP
+          cp <- add_section cp "sect1"
+          cp <- set cp "sect1" "opt1" "foo"
+          cp <- set cp "sect2" "opt2" "bar"
+          options cp "sect1"
+     ,TestLabel "chaining3" $ TestCase $ 
+      ["opt1", "opt2"] @=? (
+       forceEither $ do let cp = emptyCP
+                        cp <- add_section cp "sect1"
+                        cp <- set cp "sect1" "opt1" "foo"
+                        cp <- set cp "sect1" "opt2" "bar"
+                        options cp "sect1"
+       )
+    ]
      
 
 tests = TestList [TestLabel "test_basic" (TestList test_basic),
                  TestLabel "test_defaults" (TestList test_defaults),
                  TestLabel "test_nodefault" (TestList test_nodefault),
-                 TestLabel "test_ex_nomonad" (TestCase test_ex_nomonad)]
+                 TestLabel "test_ex_nomonad" (TestCase test_ex_nomonad),
+                 TestLabel "test_ex_errormonad" (TestList test_ex_errormonad)]

-- 
haskell-testpack