load "Int";
exception notdone;

datatype hexp_t = x_num of int | x_true | x_false | x_net of string
;

fun sfold f nil = ""
|   sfold f [item] = f item
|   sfold f (h::t) = (f h) ^ ", " ^ (sfold f t)
;

fun xToStr (x_num n) = Int.toString n
|   xToStr (x_true) = "true" 
|   xToStr (x_false) = "false" 
|   xToStr (x_net s) = s
|   xToStr (_) = "??" 
;


fun printgate (id, contacts) = print("  " ^ id ^ "(" ^ sfold xToStr contacts ^ ");\n");


val k = ref 0;
val gates = ref nil;
fun loggate g = (printgate g; gates := g :: !gates); 
fun funique id = id ^ Int.toString(!k) before k := !k + 1;
fun newnet() = x_net(funique "n");

fun gen_gate(id, contacts) = 
    let val r = x_net(funique "g")
    val _ = loggate(id, r :: contacts)
    in r end
;

fun gen_buffer(a, b) = loggate("BUF", [a, b]);

fun gen_and2(x_false, b) = x_false
|   gen_and2(x_true, b) = b
|   gen_and2(a, x_false) = x_false
|   gen_and2(a, x_true) = a
|   gen_and2(a, b) = gen_gate("AND2", [a, b]);
;

fun gen_not(x_true) = x_false
|   gen_not(x_false) = x_true
|   gen_not(a) = gen_gate("INV", [a])
;


fun gen_or2(x_false, b) = b
|   gen_or2(x_true, b) = x_true
|   gen_or2(a, x_false) = a
|   gen_or2(a, x_true) = x_true
|   gen_or2(a, b) = gen_gate("OR2", [a, b]);
;

fun gen_mux2(x_true, l, r) = l
|   gen_mux2(x_false, l, r) = r
|   gen_mux2(g, l, r) = if l=r then l else gen_gate("MUX2", [g, l, r])
;

fun gen_dff(a) = gen_gate("DFF", [a, x_net "clk"]);


(* Build converts an expression into logic gates.
 * It should perhaps check for sub-expressions already made !
 *)

fun build (Num n) = if n=0 then x_false else x_true
|   build (Net s) = x_net s
|   build (Inv v) = gen_not(build v)
|   build (Diadic(D_and, a, b)) = gen_and2(build a, build b)
|   build (Diadic(D_or, a, b))  = gen_or2(build a, build b)
|   build (Diadic(D_xor, a, b)) = gen_xor2(build a, build b)
|   build (Query(g, a, b)) = gen_mux2(build g, build a, build b)
;

(* end of gatebuilder *)