Simple examples of converting to binary bit lane form:

| pandex w (Num n) = if n = 0 then [ x_false ]	else 
    let fun k 0 = nil  (* lsb first *)
	|   k n = (if (n mod 2)=1 then x_true else x_false) :: k (n div 2)
        fun q 0 = [x_true]  (* final negative sign bit *)
	|   q n = (if (n mod 2)=0 then x_true else x_false) :: q (n div 2)
	in if (n >= 0) then k n else sex w (q (0-1-n)) end

Example:  -4 in a 6 bit field is 111100.


> pandex 6 (Num ~4)
it = [ x_false, x_false, x_true, x_true, x_true, x_true ]

Hold lists least significant bit first to make adders easier!


Example: conditional expression: a broadside multiplexor:



| pandex w (Query(g, t, f)) = 
    let val t' = pandex w t
        val f' = pandex w f
	fun k([], []) = []
	|   k(a, nil) = k(a, [ false ])
	|   k(nil, b) = k([ false ], b)
	|   k(a::at, b::bt) = gen_mux2(g, a, b) :: k(at, bt)
	in k(t', f') end

> pandex 3 (Query(Net "g", [Net "t0",  Net "t1"], [Num 5]))
  MUX2(u10, g, t0, VCC);
  MUX2(u11, g, t1, GND);
  MUX2(u12, g, GND, VCC);
it = [ Net "u10", Net "u11", Net "u12" ]

Or if we have some simple peepholes enabled we get:
> pandex 3 (Query(Net "g", [Net "t0",  Net "t1"], [Num 5]))
  MUX2(u20, g, t0, VCC);
  AND2(u21, g, t1);
  INV(u22, g)
it = [ Net "u20", Net "u21", Net "u22" ]



Exercise: write the pandex clauses for the left and right shift operators.