On: The Q Language

[kazinator]

I don't see where this code is getting a definition for K. (The return type of the ctype function).

It's not in the "k.h" header, though that references it also.

Maybe the build system injects it through the compiler command line or a forced-include header. Though the gcc command line alluded to in the block comment header shows no evidence of that.

Edit: Found it! It's a typedef for a pointer to a struct k0:

  typedef struct k0{signed char m,a,t;C u;I r;union{G g;H h;I i;J j;E e;F f;S s;struct k0*k;struct{J n;G G0[1];};};}*K;

[hoosieree → kazinator]

That's the dominant data structure in the whole program. It's a little different from what's used in APL and J, but essentially it represents an array which carries around its length, shape, and pointer to items. An explanation for the J version is in An Implementation of J [1].

There are a handful of helper functions to get/set various parts of this structure, and most of the functions in the language (and its implementation) take 1 or 2 of these and return 1.

[1]: http://sblom.github.io/openj-core/iojNoun.htm#Arrays