Re: [Haskell-cafe] SmallCheck and parser testing

3 Apr 2007

      On Tue, 3 Apr 2007 16:01:56 +0100
Joel Reymont  wrote:
...
Folks,
I'm trying to figure out how to test a Parsec-based parser with  
Smallcheck [1]. My test AST is below and the goal is to return  
StyleValue <Int here> if the parser is fed an integer, or return  
Solid when parsing "Solid", etc.
data Style
     = StyleValue Expr
     | Solid
     | Dashed
     | Dotted
     | Dashed2
     | Dashed3
     deriving Show
I figure that the following is needed somehow:
instance Serial Style where
     series = cons1 StyleValue . depth 0
              \/ cons0 Solid
              \/ cons0 Dashed
              \/ cons0 Dashed2
              \/ cons0 Dashed3
              \/ cons0 Dotted
My parser is 'style', so I would be passing it as p below
run p input =
     case (parse p "" input) of
       Left err -> do { putStr "parse error at "
                      ; print err
                      }
       Right x -> x
How do I go from here to making sure my parser is valid?
There are several ways to check your parser.  If you have a pretty
printer, you can check that the parse of a pretty printed term is equal
to the term itself.

\begin{code}
parseEq :: String -> Style -> Bool
parseEq s t = case parse style "" s of
                   Left err -> False
                   Right x  -> x == t

prop_parsePretty t = parseEq (pretty t) t
\end{code}

You can also use a unit-testing style.  Imagine you have a list of
strings and the correct parse trees for each.  You can then check that
the parses match the expected results.

\begin{code}
knownParses :: [(String, Style)]
knownParses = ???

prop_unitTest = all (uncurry parseEq) knownParses
\end{code}

Cheers,
Spencer Janssen
...
I thought of the following property (thanks sjanssen)
prop_parse p s =
     show (run p s) == s
but I don't know how to proceed from here.
Thanks, Joel
[1] http://www.cs.york.ac.uk/fp/darcs/smallcheck/
--
http://wagerlabs.com/
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