[TUHS] Re: uphill both ways, was Re: What would early alternatives to C have been?

[Bakul Shah via TUHS <tuhs@tuhs.org>]


On Mar 10, 2025, at 7:26 PM, John Levine <johnl@taugh.com> wrote:
> 
> In my 1971 compiler course at Yale, Alan Perlis made us try to write a compiler
> that translated a subset of APL into Basic. He suggested we write it in APL,
> which was a terrible idea, so I wrote it in Trac, for which I happened to have
> written my own interpreter.
> 
> I think my compiler was the only one that worked, and it was pretty clever,
> turning the APL array expressions into structures with array boundaries and
> example expressions, with no array temporaries. It only generated the loops to
> evaluate the expressions when storing into another array.
> 
> Someone got a PhD in 1978 for a similar compiling technique but in 1971 I was a
> 17 year old twerp so what did I know?
> 
> R's,
> John

Pretty impressive for a 17yo!

Isn’t APL syntax rather context sensitive[1]? Neither yacc nor
a RD parser would’ve helped! Unless the subset was limited to a
context free subset.

Tim Budd in his 1978 work made quite a few changes to APL to
ease compilation and used yacc. [I have the book somewhere....]

[1] I do not recall if Iverson's original APL had a context sensitive
grammar but modern APLs do.
 
Given an expression ‘x y z’, its parse depends on the types of
x, y & z. Example: y(x,z) if y is a dyadic verb, x & z are values,
x(y(z)) if x & y are monadic verbs, z a value etc.