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

["John R Levine" <johnl@taugh.com>]

On Tue, 11 Mar 2025, Bakul Shah wrote:
>> 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.

APL at the time had a very simple syntax, once you got past all the 
special characters.  I wrote my compiler on a PDP-10 with ASCII terminals 
so I just used keywords like IOTA.

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

There's a copy at the Internet Archive.  He and I were at Yale at the same 
time and we knew each other a little, but neither of us was aware that 
we'd come up with such similar techniques.

> 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.

You do need to know whether a symbol is a variable or some kind of 
function, but that's not hard.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly