Hello everybody!
================
I love Haskell and it has helped me a lot to understand geometric
modelling, the subject of my diploma thesis.
But I have encountered a serious problem. I would like to have lists
of instances of a class, but it doesn't seem possible. I have
played around with new data-declarations, but what I actually need is
the comfortable flexibility of Haskell built-in lists.
I have written the program below which produces the nice output
["Instance_One", "Instance_One", "Instance_One"]
["Instance_Two", "Instance_Two", "Instance_Two"]
["Baseclass", "Baseclass", "Baseclass"]
But I would like to have a program with the following output:
["Instance_One", "Instance_Two", "Baseclass"]
So my question to all Haskell experts is: Is there any way to obtain
this output in the way I conceived? Or am I simply too stupid?
looking forward to hear from anybody, Greetings, Sven.
PS. Please write back to the address below, if you don't mind.
======================================================================
import GHCio
import Channel
class Baseclass m where
showme::m->String
showme m = "Baseclass"
data Instance_One = Inst_One
instance Baseclass Instance_One where
showme m = "Instance_One"
data Instance_Two = Inst_Two
instance Baseclass Instance_Two where
showme m = "Instance_Two"
instance Baseclass Integer
list_one = [Inst_One,Inst_One,Inst_One]
list_two = [Inst_Two,Inst_Two,Inst_Two]
list_base::[Integer]
list_base = [1,2,3]
-- ### This is what I need but Haskell won't let me do that ###
-- list_needed::[Baseclass]
-- list_needed = [Inst_One,Inst_Two,2]
showlist::Baseclass m => [m]->String
showlist l = show (map showme l) ++ "\n"
main = putStr $ (showlist list_one )
++ (showlist list_two )
++ (showlist list_base)
-- ++ (showlist list_needed)
======================================================================
--
-----------------------------------------------------------------------
Sven Havemann, Rosental 24, 53111 Bonn, Deutschland, 0049/228/656860
Keywords: Freeform Curves & Surfs, Generative Modeling, 4D Animation
FG Computergrafik: Institut f. Informatik III
Universitaet Bonn Tel: (0228) 73-4315/-4292, Fax: -4382
Roemerstr. 164, Mail: [EMAIL PROTECTED]
D-53117 Bonn, Deutschland WWW: http://hyperg.cs.uni-bonn.de/~havemann
-----------------------------------------------------------------------
