Low, high bytes of word.

README.markdown

@@ -463,22 +463,22 @@ We cannot absolute-indexed a word.
     | }
     ? indexed access of non-table
 
-> We cannot absolute acess a word.
-> 
->     | assign word screen 1024
->     | routine main {
->     |    lda screen
->     | }
->     ? absolute access of non-byte-based address
-> 
-> Instead, we have to do this.
-> 
->     | assign word screen 1024
->     | routine main {
->     |    lda <screen
->     |    lda >screen
->     | }
->     = True
+We cannot absolute access a word.
+
+    | assign word screen 1024
+    | routine main {
+    |    lda screen
+    | }
+    ? absolute access of non-byte-based address
+
+Instead, we have to do this.
+
+    | assign word screen 1024
+    | routine main {
+    |    lda <screen
+    |    lda >screen
+    | }
+    = True
 
     -> Tests for functionality "Emit ASM for SixtyPical program"
     
@@ -495,6 +495,8 @@ We cannot absolute-indexed a word.
     |    lda screen, x
     |    lda screen, y
     |    lda (screen), y
+    |    lda <score
+    |    lda >score
     |    inc screen
     |    tax
     |    inx
@@ -541,6 +543,8 @@ We cannot absolute-indexed a word.
     =   lda screen, x
     =   lda screen, y
     =   lda (screen), y
+    =   lda score
+    =   lda score+1
     =   inc screen
     =   tax
     =   inx

src/SixtyPical/Emitter.hs

@@ -49,6 +49,9 @@ emitInstr p r (COPY (NamedLocation st label) A) = "lda " ++ label
 emitInstr p r (COPY (NamedLocation st label) X) = "ldx " ++ label
 emitInstr p r (COPY (NamedLocation st label) Y) = "ldy " ++ label
 
+emitInstr p r (COPY (LowByteOf (NamedLocation st label)) A) = "lda " ++ label
+emitInstr p r (COPY (HighByteOf (NamedLocation st label)) A) = "lda " ++ label ++ "+1"
+
 emitInstr p r (COPY A X) = "tax"
 emitInstr p r (COPY A Y) = "tay"
 emitInstr p r (COPY X A) = "txa"

src/SixtyPical/Model.hs

@@ -39,6 +39,8 @@ data StorageLocation = A
               | Indexed StorageLocation StorageLocation
               | IndirectIndexed StorageLocation StorageLocation
               | NamedLocation (Maybe StorageType) LocationName
+              | LowByteOf StorageLocation
+              | HighByteOf StorageLocation
     deriving (Show, Ord, Eq)
 
 -- this is bunk, man.  if a location does not appear in an analysis

src/SixtyPical/Parser.hs

@@ -122,10 +122,24 @@ index = do
         "y" -> Y
 
 data AddressingModality = Directly LocationName
+                        | HighBytely LocationName
+                        | LowBytely LocationName
                         | Indirectly LocationName
                         | Immediately DataValue
     deriving (Ord, Show, Eq)
 
+low_byte_of_absolute :: Parser AddressingModality
+low_byte_of_absolute = do
+    string "<"
+    l <- locationName
+    return $ LowBytely l
+
+high_byte_of_absolute :: Parser AddressingModality
+high_byte_of_absolute = do
+    string ">"
+    l <- locationName
+    return $ HighBytely l
+
 indirect_location :: Parser AddressingModality
 indirect_location = do
     string "("
@@ -148,7 +162,9 @@ immediate = do
 
 addressing_mode :: (AddressingModality -> [StorageLocation] -> Instruction) -> Parser Instruction
 addressing_mode f = do
-    d <- ((try immediate) <|> (try indirect_location) <|> direct_location)
+    d <- ((try immediate) <|> (try high_byte_of_absolute) <|>
+          (try low_byte_of_absolute) <|> (try indirect_location) <|>
+          direct_location)
     indexes <- many index
     return $ f d indexes
 
@@ -319,6 +335,8 @@ lda = do
     addressing_mode gen
     where
        gen (Immediately v) [] = COPY (Immediate v) A
+       gen (LowBytely l) [] = COPY (LowByteOf (NamedLocation Nothing l)) A
+       gen (HighBytely l) [] = COPY (HighByteOf (NamedLocation Nothing l)) A
        gen (Directly l) [] = COPY (NamedLocation Nothing l) A
        gen (Directly l) [reg] = COPY (Indexed (NamedLocation Nothing l) reg) A
        gen (Indirectly l) [reg] = COPY (IndirectIndexed (NamedLocation Nothing l) reg) A