3 files changed, 87 insertions, 27 deletions
diff --git a/kernel/main.dats b/kernel/main.dats
index e7a68f5..bbec179 100644
--- a/kernel/main.dats
+++ b/kernel/main.dats
@@ -1,16 +1,7 @@
 #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
+staload "kernel/writer.sats"
+dynload "kernel/writer.dats"
 
 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) =
@@ -19,19 +10,4 @@ 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
-
+implement main0 () = print_char('X')
diff --git a/kernel/writer.dats b/kernel/writer.dats
new file mode 100644
index 0000000..7d0383f
--- /dev/null
+++ b/kernel/writer.dats
@@ -0,0 +1,57 @@
+#include "share/atspre_staload.hats"
+
+staload "kernel/writer.sats"
+
+extern castfn i2u8 {n: nat} (i: int n): uint8 n
+
+fun color_value(c : color): uint8 = 
+  case+ c of 
+    | Black() => i2u8 0
+    | Blue() => i2u8 1
+    | Green() => i2u8 2
+    | Cyan() => i2u8 3
+    | Red() => i2u8 4
+    | Magenta() => i2u8 5
+    | Brown() => i2u8 6
+    | LightGray() => i2u8 7
+    | DarkGray() => i2u8 8
+    | LightBlue() => i2u8 9
+    | LightGreen() => i2u8 10
+    | LightCyan() => i2u8 11
+    | LightRed() => i2u8 12
+    | Pink() => i2u8 13
+    | Yellow() => i2u8 14
+    | White() => i2u8 15
+
+fun code_value(foreground: color, background:color): uint8 = 
+  (color_value(background) << 4) lor color_value(foreground)
+
+fun output_char(c : char, writer : !writer) : void = let
+  val p = writer.buffer.1
+  val () = p->[writer.column_position] := @{ ascii_character = c , color_code = writer.color_code }
+in
+  ()
+end
+
+%{^
+  #define get_vram() ((void *) 0xB8000 + 1988)
+%}
+
+extern fun get_vram():<> [l: addr] (@[screenChar][N] @ l | ptr l) = "mac#"
+
+extern prfun eat_writer (pf: writer): void
+
+extern castfn uint8_of {n: nat} (i: int n): uint8 n
+
+implement print_char(c : char) : void = let
+  val (pf_vram | vram) = get_vram()
+  val writer = @{
+    column_position = i2sz 0,
+    color_code = code_value(Yellow,Black),
+    buffer = (pf_vram | vram)
+  }
+in 
+  output_char(c,writer);
+  let prval () = eat_writer writer in () end
+end
+
diff --git a/kernel/writer.sats b/kernel/writer.sats
new file mode 100644
index 0000000..c9b8814
--- /dev/null
+++ b/kernel/writer.sats
@@ -0,0 +1,27 @@
+#define N 80 * 25
+
+datatype color =
+  | Black 
+  | Blue 
+  | Green 
+  | Cyan 
+  | Red 
+  | Magenta 
+  | Brown 
+  | LightGray 
+  | DarkGray 
+  | LightBlue 
+  | LightGreen 
+  | LightCyan 
+  | LightRed 
+  | Pink 
+  | Yellow 
+  | White 
+
+
+typedef screenChar = @{ ascii_character = char, color_code = uint8}
+
+vtypedef tptr (a: t@ype, l:addr) = (a @ l | ptr l)
+vtypedef writer = [l: addr] [n:nat | n < N] @{ column_position = size_t n, color_code = uint8 , buffer = tptr(@[screenChar][N],l)}
+
+fun print_char(c : char) : void