🚀 go-pugleaf

In article <BJORNL.90Jul28100843@tarpon.tds.kth.se> bjornl@tds.kth.se (Bj|rn Lisper) writes:
% For instance, if(b,x,y) defined by
% 
% b => if(b,x,y) = x
% not b => if(b,x,y) = y
% 
% is a (non-strict) function in three arguments. Left-to-right lazy evaulation
% will give the ordinary "conditional" semantics. As I pointed out, there are
% cases where other evaluation orders terminate whereas this doesn't.

If you want a different evaluation order you can define it (in
Miranda) like this:

> if b x x = x
> if True x y = x
> if False x y = y

Now if is strict in its second and third arguments but not its first
one.

% Of course. A more interesting example is multiplication, that strictly
% speaking (sic!) is non-strict, since whenever one argument returns zero the
% other argument is not needed. if f(x) is non-terminating, then 0*f(x) still
% terminates (and returns zero) if '*' is treated as a non-strict function
% with left-to-right evaluation order. Is '*' usually implemented as a strict
% or as a non-strict operator in lazy functional languages?

Strict, since if you don't like this you can easily roll your own:

> 0 $times y = 0
> x $times y = x*y

Tim