Need some help please

[Nick Name]

On Wed, 27 Aug 2003 15:08:32 +0100
"Rajiv Patel" <raj_patel@cwcom.net> wrote:

> 1.	a conditional expression 

This one uses "case" so it should solve your homework; moreover it uses
an orthogonal matrix (as long as you pay attention to the value assigned
to f, of course) so it is safe.

---- cut here ---

-- First of all, a simple auxiliary function, so everything is 
-- tail recursive

safetailaux :: [b] -> ([b] -> Int) -> [b]
safetailaux b d = a b c
    where c = d b
	  f = f
	  m = const False

	  a c z = case z of
			 1 -> e g  -- this matrix is orthogonal
			 0 -> g f  -- so the function "a" is safe

	  e g = filter m []
	  g e = drop 1 b -- like all functions it can be defined as
			 -- a filter and a drop

-- Now make it no longer tail recursive
safetail x = safetailaux x ((\ z -> if z == 0 then 1 else 0) . length)

--- cut here ---

For the pattern matching case, it's easier:

safetailPM [x,y,z] = tail [x,y,z]
safetailPM a@[x,y] = tail a
safetailPM x = x

For the other one, try to figure out how it works from my examples

Hope this helps 

Vincenzo