Switch decoding over to a Monad for portability

At some point this may run on BizHawk so that I can draw information instead of having the very limited Dolphin text.

I should really start working on my own Amulet prelude... There's lots of stuff from cats that I miss here.

mem/decode.ml

@@ -1,5 +1,40 @@
 open import "prelude.ml"
+open import "./int.ml"
+open import "../reader.ml"
+
+type decoding_context = DecodingContext of {
+  read_u8 : int -> u8,
+  read_s8 : int -> s8,
+  read_u16 : int -> u16,
+  read_s16 : int -> s16,
+  read_u32 : int -> u32,
+  read_s32 : int -> s32
+}
 
 class decode 'a begin
-  val decode : int -> 'a
+  val decode : int -> reader decoding_context 'a
+end
+
+instance decode u8 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_u8 addr)
+end
+
+instance decode s8 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_s8 addr)
+end
+
+instance decode u16 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_u16 addr)
+end
+
+instance decode s16 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_s16 addr)
+end
+
+instance decode u32 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_u32 addr)
+end
+
+instance decode s32 begin
+  let decode addr = Reader (fun (DecodingContext c) -> c.read_s32 addr)
 end

mem/int.ml

@@ -1,6 +1,4 @@
 open import "prelude.ml"
-open import "./decode.ml"
-open import "../dolphin.ml"
 
 type u8 =
   U8 of int
@@ -9,10 +7,6 @@ instance show u8 begin
   let show (U8 x) = (show x) ^ "_u8"
 end
 
-instance decode u8 begin
-  let decode addr = U8 (Dolphin.read_value_8 addr)
-end
-
 type s8 =
   S8 of int
 
@@ -20,17 +14,6 @@ instance show s8 begin
   let show (S8 x) = (show x) ^ "_s8"
 end
 
-instance decode s8 begin
-  let decode addr =
-    let u8 = Dolphin.read_value_8 addr
-    let signfix =
-      if u8 > 0xFF then
-        negate (0x100 - u8)
-      else
-        u8
-    S8 signfix
-end
-
 type u16 =
   U16 of int
 
@@ -38,10 +21,6 @@ instance show u16 begin
   let show (U16 x) = (show x) ^ "_u16"
 end
 
-instance decode u16 begin
-  let decode addr = U16 (Dolphin.read_value_16 addr)
-end
-
 type s16 =
   S16 of int
 
@@ -49,17 +28,6 @@ instance show s16 begin
   let show (S16 x) = (show x) ^ "_s16"
 end
 
-instance decode s16 begin
-  let decode addr =
-    let u16 = Dolphin.read_value_16 addr
-    let signfix =
-      if u16 > 0xFFFF then
-        negate (0x10000 - u16)
-      else
-        u16
-    S16 signfix
-end
-
 type u32 =
   U32 of int
 
@@ -67,10 +35,6 @@ instance show u32 begin
   let show (U32 x) = (show x) ^ "_u32"
 end
 
-instance decode u32 begin
-  let decode addr = U32 (Dolphin.read_value_32 addr)
-end
-
 type s32 =
   S32 of int
 
@@ -78,13 +42,20 @@ instance show s32 begin
   let show (S32 x) = (show x) ^ "_s32"
 end
 
-instance decode s32 begin
-  let decode addr =
-    let u32 = Dolphin.read_value_32 addr
-    let signfix =
-      if u32 > 0xFFFFFFFF then
-        negate (0x100000000 - u32)
-      else
-        u32
-    S32 signfix
-end
+let u8_to_s8 (U8 u8) =
+  if u8 > 0x7F then
+    S8 (0x100 - u8)
+  else
+    S8 u8
+
+let u16_to_s16 (U16 u16) =
+  if u16 > 0x7FFF then
+    S16 (0x10000 - u16)
+  else
+    S16 u16
+
+let u32_to_s32 (U32 u32) =
+  if u32 > 0x7FFFFFFF then
+    S32 (0x100000000 - u32)
+  else
+    S32 u32