SmallCheck and parser testing
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? 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/
On Tue, 3 Apr 2007 16:01:56 +0100
Joel Reymont
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/
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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'd use QuickCheck rather than SmallCheck. First write Arbitrary instances for Style and Expr (plus obviously any other types used by Expr). Then write another generator that converts a Style to a string with random formatting (whitespace, comments etc). Then assert that the
On Tue, 3 Apr 2007 16:01:56 +0100
Joel Reymont
participants (3)
-
Joel Reymont -
Paul Johnson -
Spencer Janssen