Hi,
Jose> I am working on an Computer Algebra system to transform
Jose> mathematic expressions, possibly simplifing them. There is a
Jose> data type to represent the expressions:
Jose> data Expr = Int Integer | Cte String | Var String | App Fn [Expr]
Jose> An expression may be an integer, a named constante (to
Jose> represent "known" contantes like pi and e), a variable or an
Jose> application. An application has a functor (function name) and
Jose> a list of arguments. The functor is introduced with
Jose> data Fn = Sum | Pro | Pow
Jose> meaning the application may be a sum, a product or a power.
...
Jose> The functions manipulating the expressions also should be
Jose> extensible to accomodate new algorithms. The extensions is in
Jose> a form of hooks (based on the Fn component of an application
Jose> function) in the main algorithms.
I've encountered the same problem and I'm interested to get to know a
highly productive way which at the same time can be considered
a good way of software engineering.
Not enough ... it should pass the Haskell typechecker and be compatible
with the class concept.
At the moment, I know only one "right way": to define several different
types and define functions on each of these types individually.
That's too much work for me ...
However, the only fast but awful style I know is something like:
data FunctorType = Sum | Pro | Pow | Sin | Trace | UnsafeInput
| ... whatever you like
data AllMyExpressions = SingleConstructor { functor: FunctorType,
arguments: [AllMyExpressions] }
--
Christoph Herrmann
E-mail: [EMAIL PROTECTED]
WWW: http://brahms.fmi.uni-passau.de/cl/staff/herrmann.html
