#include "share/atspre_staload.hats"

%{^
  #define get_vram(_) ((void *) 0xB8000 + 1988)
%}

typedef cell = @{ ch = char, attrib = uint8 }

extern fun get_vram {n: nat} (n : size_t n):<> [l: agz] (@[cell][n] @ l | ptr l) = "mac#"

extern prfun eat_vram {l: agz} {n: int} (pf: @[cell][n] @ l): void

extern castfn uint8_of {n: nat} (i: int n): uint8 n

fn string_length {n:nat} (str: string (n)) : size_t (n) = let
  fun loop {i:nat | i <= n} .<n-i>. (str: string n, i: size_t i): size_t (n) =
    if string_isnot_atend (str, i) then loop (str, succ(i)) else i
in
  loop (str, i2sz(0))
end

implement main0 () = let
  val hello = "Hello world!"
  val length = string_length hello
  val color_byte = 0x1f
  val (pf_vram | vram) = get_vram(length)
  fun loop {l : agz} {n,i: nat | i <= n} .<n-i>. (pf: !(@[cell][n] @ l) | n : size_t n, i : int i, p : ptr l, str: string (n)) : void = 
    if n > i then (
      p->[i] := @{ ch = str[i], attrib = uint8_of color_byte };
      loop(pf | n,i+1,p,str))
    else ()

in
  loop(pf_vram | length, 0, vram, hello);
  let prval () = eat_vram pf_vram in () end
end