🚀 go-pugleaf

In article <4170@castle.ed.ac.uk> nick@lfcs.ed.ac.uk (Nick Rothwell) writes:
>Correct me if I'm wrong (more than likely...) but in a lazy language
>I can write things like
>
>	fun f x = cons(1, f x)
>
>to build an infinite list, but not
>
>	fun f x = reverse_cons(f x, 1)
>
>because of the reduction order.

If you apply a printing function to the second you might get a "(" on
the screen and then the program will hang, but that is to do with the
strictness of the printing function.  It's the printing function which
has defined an evaluation order, in effect.  However, if I were to
pattern match

        fun last (reverse_cons(x,a)) = a

a call of "last (f x)" should return "1" (BTW, what's that "x" for?).

I believe there is an Oxford DPhil thesis by a man called David Turner
which pointed out that strict languages are not referentially
transparent because of the fact that conditionals are not strict, so
that the equality symbol in the definition

        fun iiff (b,x,y) = if b then x else y

is not equality.  Lazy evaluation languages are referentially
transparent.  I think this is what the original poster meant by
"purer".

>		Nick.
>--
>Nick Rothwell,	Laboratory for Foundations of Computer Science, Edinburgh.
>		nick@lfcs.ed.ac.uk    <Atlantic Ocean>!mcsun!ukc!lfcs!nick
>~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~
>		   Ich weiss jetzt was kein Engel weiss

						Geoff Barrett


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