Good layout style? (was: Re: "where" block local to a guard?)

[Dr Mark H Phillips]

On Wed, 2002-09-18 at 01:26, Hamilton Richards wrote:
> You can get the effect you're after by using let-expressions:
> 
> >  functn :: Int -> Int
> >  functn i
> >      | i>5       = let t = functn (i-2) in t * i
> >      | i>0       = let t = functn (i-1) in t * i
> >      | otherwise = 1
> 
> 'where' is part of the syntax of definitions, not expressions. This 
> enables a name defined in a where-clause to be used in more than one 
> guarded expression.

Thanks for this!  It would seem "let ... in ..." is what I want.

But I'm a bit confused about how to use the off-side rule in
conjunction with let.  Do I do:

    let a=1
        b=2
        c=3
    in a*b*c

or do I do:

    let
    a=1
    b=2
    c=3
    in
    a*b*c

or, in the context of a guard, do I do:

    | i>5      = let a=1; b=2; c=3
      in a*b*c

Basically I'm a bit confused about how the offside rule
works in various situations.

With "if ... then ... else ..." I don't know whether I should be doing

  f x = if x>5 
    then x*x 
    else 2*x

or

  f x = if x>5
        then x*x
        else 2*x

or

  f x = if x>5
          then x*x
            else 2*x

or what!

Hugs seems to think they are all legal.  Is there any rational as to
how to do layout?  Any tips would be greatly appreciated!

Thanks,

Mark.