I myself am fairly new to Haskell and I'm trying to understand Monads better
myself, but maybe this could help?
http://user.cs.tu-berlin.de/~magr/pub/Transformers.en.html
It's a little out of date and won't compile cleanly on newer instances of
GHC without changing all the instances of Map.lookup ... to return $
fromJust Map.lookup, but once you make that small change it works fine.
Also, I'm not familiar with the QuickCheck package, but I browsed through it
quickly and Test.QuickCheck.Monadic caught my eye. Perhaps a State or StateT
combined with IdM or PropertyM would do what you want?
On Tue, Sep 15, 2009 at 5:56 PM, Alexander MacDonald
Hi guys, I¹ve been using quickcheck for a while and I¹m having no problem making generators for my data types, however recently I stumbled upon a situation where I need to maintain State inside the quickcheck generator functions. Here's a simple example, imagine I've got a basic language which only has two features, variable definitions and assignments:
type Script = [Statement]
data Name = Name String deriving (Show,Eq)
data Statement = Def Name Int | Assign Name Name deriving Show
Generating random scripts is easy enough, just make each type an instance of Arbitrary with a suitable generator function, however I want to make sure that the generated scripts are syntactically valid. In this case that means no "Name" can be used in an "Assign" statement unless it has previously been defined by a "Def" statement.
My knowledge of using monads is somewhat basic so I'm struggling to figure out how to use the State monad with QuickCheck. I've pasted my current effort on the web: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=9412
If anyone could spare a moment to glance at my code and give me a push in the right direction that would be much appreciated!
Thanks, Alex Mac
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