Re: [stack] Joy's relationship to FP + a Joy variant with combining forms

John Nowak scripsit:

> What I'm desperately curious about is why certain languages like FP,  
> APL, J, etc, avoid first class functions. Obviously there are  
> advantages to only having first order functions, and I see a few ways  
> this is useful (termination proofs are much easier, etc), but I'm  
> admittedly less informed on this subject than I'd like to be. If  
> anyone would be willing to point me in the direction of something that  
> discusses the advantages of the FP/APJ/J approach in contrast to the  
> ML/Haskell approach, I'd be very grateful. Unfortunately, most papers  
> on FP seem to be locked away on sites I don't have access to, which is  
> doubly bad as there are so few to begin with.

I don't really know either, but one thing that comes to mind is that these
languages are classically implemented using dynamic-binding interpreters,
which don't mix very well with first-class functions (the Lisp "funarg
problem").  Although as long ago as 1977, HP implemented APL using a
JIT compiler, with as far as I know no effects on the language except
the loss of "eval".

The paper describing it, (Eric J. Van Dyke, A Dynamic Incremental Compiler
for an Interpretative Language, HP Journal, pp. 17-24, July 1977), is
not online as far as I can tell, but in brief: Each line of APL code
was compiled into machine code as it was encountered, specializing the
code to assume that the rank, shape, and type of the variables mentioned
in it were fixed.  A prologue, also JIT-compiled, assured that this was
still true when the line was next executed.  If the assumption failed,
the line was recompiled using a different strategy which assumed that
rank and type were fixed but not shape; further failures caused this
second strategy to be repeated.  This technique squeezed almost all the
polymorphism out of actual APL programs.

-- 
Income tax, if I may be pardoned for saying so,         John Cowan
is a tax on income.  --Lord Macnaghten (1901)           [email protected]