Perspectives on learning and using Haskell
ddarius at hotpop.com
Fri Jan 2 02:44:23 EST 2004
On Thu, 1 Jan 2004 21:07:00 -0500
ajb at spamcop.net wrote:
> > (6) I have found that Haskell seems to a particularly effective
> > platform for pursuing some ideas of extreme programming,
> There you go. :-)
> There is only one problem I've found with test-driven development in
> Haskell. In C++, it's possible to break the "module" abstraction
> (yes, I know, C++ doesn't have modules; it has classes, which are
> really instantiable modules) by using "friend". In Haskell, I find
> myself occasionally having to expose parts of a module which I would
> prefer not to, in order for the unit tests suite to do their job
> I wonder if there might be a way to fix this, say, by allowing modules
> to selectively expose parts of their interface depending on who wants
> to use it.
Well, the quick and dirty solution (at least with GHC) is to use GHCi
and interpret the modules, which should keep some internals readily
accessible. For example, I use the new -e option of GHC to run my unit
The "nicer" way*, though it could use less typing and "extraneous"
files, is simply use multiple modules.
module FooInternals where
publicFoo :: Foo -> Bar
publicFoo x = privateFrob x
privateFrob x :: Foo -> Bar
privateFrob x = ...
debugFoo :: (Foo -> Bar) -> Foo -> Bar
debugFoo f x = ...
module Foo ( publicFoo ) where
module FooDebug ( publicFoo, debugFoo ) where
* Okay, so it doesn't really solve the "problem", it's just a way of
structuring that avoids it.
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