(* AST for a K-like language *)

use "arr.sml"; (* TODO: open, nto use, for compiled version *)

datatype ast = Leaf of arr
             | Nilad of unit -> arr
             | Monad of (arr -> arr) * ast
             | Dyad of ((arr * arr) -> arr) * ast * ast;
             (* TODO: higher-arity functions, projections &c.  Unless you just
                want to do an APL rather than a K? *)

fun eval_ast(t) = case t of
                       Leaf(a)     => a
                     | Nilad(f)    => f()
                     | Monad(f,r)  => f(eval_ast(r))
                     | Dyad(f,l,r) => f(eval_ast(l),eval_ast(r));

(* TODO: codegen_ast (eval_ast evaluates it in ML, but we need to output ASM!) *)

(*
(* Test data *)
val x = S(N(0w2));
val y = S(N(0w3));
val a0 = A(x,y);
val a1 = A(A(A(x,y),x),y);
fun f() = S(N(0w4)); (* nilad *)
fun g(x) = A(x,x); (* monad *)
fun h(x,y) = A(x,y); (* dyad *)
val t0 = Leaf(x);
val t1 = Leaf(a0);
val t2 = Leaf(a1);
val tn = Nilad(f);
val tm = Monad(g,t1);
val td = Dyad(h,t1,t2);
*)