Re: [stack] stackless fixed-arity concatenative languages

On May 22, 2008, at 3:38 AM, John Nowak wrote:

> The kind people on #concatenative also pointed out that 'dup dip dip'
> behaves differently than the version of 'bi@' in Factor because it
> applies the quotation to 'y' first, not 'x'. In an impure language,
> these are obviously not equivalent. A definition that matches the
> semantics of 'bi@' in Factor is 'dup [ dip ] dip call', or '[ dip ]
> keep call'.

Last thought on this for tonight. I wanted to note that 'dup dip dip'  
is actually just plain wrong if you want to use it for quotations with  
arities beyond 1->1. For example, here's the Factor version of 'bi@'  
at work with a quotation of arity 1->2, 'dup':

    1 2 [ dup ] bi@
    1 2 [ dup ] dup [ dip ] dip call
    1 2 [ dup ] [ dup ] [ dip ] dip call
    1 2 [ dup ] dip [ dup ] call
    1 dup 2 [ dup ] call
    1 1 2 [ dup ] call
    1 1 2 dup
    1 1 2 2

As you can see, it applies 'dup' to both 1 and 2 as expected. Here's  
my broken version:

    1 2 [ dup ] bi@_broken
    1 2 [ dup ] dup dip dip
    1 2 [ dup ] [ dup ] dip dip
    1 2 dup [ dup ] dip
    1 2 2 [ dup ] dip
    1 2 dup 2
    1 2 2 2

Not so good. Anyway, if we use the /correct/ version of 'bi@' from  
Factor, my new system-in-progress can give it this rather nice looking  
type that very clearly shows what it does:

    $a [$B] -> $B $a $B

Maybe the trick to making n-ary combinators understandable is a more  
powerful system, not a more restricted one.

- John