I get this person may have been working with constraints we don't know about, but its not straightforward. Give this to 10 working C devs and ask them to tell you what it does without running it.
The standard cues of straightforward code aren't there -- well named variables, well named functions, comments, indentation, etc...
The APL people are not fooling around, either - look at Kx's customers: http://kx.com/Customers/end-user-customers.php . And then check how much a license for kdb+ costs per core. Oh, and "a standard purchase requires licensing at least 8 cores."
I'm curious, do you think you could tell me what some arbitrary C code does that I give you, where I've changed all the variables to "a", "b", "c", etc...? I'd be hardpressed to believe anyone in the world could.
Is APL structurally so expressive that huamns can easily extract meaning from structure? If so this is the single great accomplishment in the history of computer science. This dwarfs any contribution from Lisp, C, FORTRAN, theory of computation, etc...
And the fact that I know some of the people that worked on the original versions of APL at IBM, yet they never mentioned this, makes me suspect.
If you know the specific context ahead of time (a FSM for lexing, a hash table implementation, etc), then it really isn't that hard.* Are you honestly telling me that you wouldn't be able to figure out how a hash table implementation worked if all the types and variable names were changed to single letters? It would slow you down, sure, but it wouldn't be impossible.
* Speaking as someone who has debugged code with variable names and comments in Swedish.
That code was written with the context of, "Hey, we both know APL really well, here's a quick prototype for a new implementation of it, could you give it a look?" When somebody is showing a Scheme implementation to other Lispers, they don't need to spend time explaining what a cdr is. Context matters.
Most of the functions in that take one or two arbitrarily-dimensioned arrays and loop simple operations over them. Everything takes (w) or (a, w) and returns z. i is a loop index (as usual). w->p is the array of values in w, ga allocates a new array. ("get array"? "generic allocate?")
V1(iota){I n=*w->p;A z=ga(0,1,&n);DO(n,z->p[i]=i);R z;}
Yes, probably not. I've looked at code that I've personally written with variable names -- in the debugger and still scratched my head trying to figure out what I had done. And not trying to overstate my ability, but I tend to be someone who is generally pretty good at reading code.
Here's some code you might run across in some DSP code. There are some globals, and hopefully I translated it correctly. But in any case, w/ good function variable naming I could understand the intent in a few seconds. Without it, I think I'd scratch my head for some time. How long does it take you to figure out what it does (or what it is intended to do)?
ov f(){
xx b, hh, i, pp, j, jj = PL, k;
xx D = NN>>2*b,d=n-2*zz;
t *z[B]; t *p, m, n, q, oo;
for (i=0; i<B; i++) z[i] = &X[ro[i]*jj];
for (b=0; b<D; b++) { f(b, hh, d);
for (i=0; i<B; i++) { pp=ro[i];
k = (b << zz) + i;
p = &YY[(hh<<zz) + (pp<<(n-zz))];
for (j=0; j<B; j+=SS) { m = z[j][k];n=z[j+1][k];q = z[j+2][k];oo = z[j+3][k];
p[j]=m;p[j+1]=n;p[j+2]= q;p[j+3]=oo;}}}}About your code sample - I haven't done anything with digital signal processing code, so I couldn't tell you. It looks like some sort of wave transformation, but that's like saying code from a 3D rendering engine is "doing something with triangles", sorry.
Most of the APL functions are only a line or two long, though - that makes a big difference. "accumulate i..N", "get new vector with a[i] + w[i]", etc. The only part that is individually complex is the parser.