# [clean-list] swap from CLAS lib

G.W.M. Vissers vissers@theochem.kun.nl
Fri, 14 Sep 2001 16:50:09 +0200 (CEST)

```Hello,

I was playing around with the CLAS library (again), and noticed that
the swap function class in Clas1.icl only has instances for integers and
unboxed real arrays. Now, the following code works ok:

/////////////////////////////////////////////////////////////////////////

module bla

import StdArray, StdInt

class swap a :: *{# .a} .Int .Int -> .{# .a}

instance swap Int
where
swap x i j
| (i==j) = x
#! (xi, x) = replace x i 0
#! (xj, x) = replace x j xi
= { x & [i] = xj}

instance swap {# Real}
where
swap x i j
| (i==j) = x
#! (xi, x) = replace x i {}
#! (xj, x) = replace x j xi
= { x & [i] = xj}

Start = swap v 2 1
where
v = {1,2,3}

//////////////////////////////////////////////////////////////////////////

So, next I thought it would be nice to add an instance for unboxed integer

instance swap {# Int}
where
swap x i j
| (i==j) = x
#! (xi, x) = replace x i {}
#! (xj, x) = replace x j xi
= { x & [i] = xj}

and changed the Start function to

Start = swap v 2 1
where
v = {{1,2,3}, {2,3,4}, {3,4,5}}

Now, the compiler complains:
Error [bla.icl,25,swap ({#})]: swap ({#}) multiply defined symbol

which seems pretty weird to me, because I always thought that integers and
reals were pretty different. So, the question is: what goes wrong here? Is
it possible to use the same class also for swapping rows in an integer
matrix?

Thanks for any pointers,

Gé Vissers

```