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-- Assembler for Hack Computer
-- Coursework for Nand2Tetris
-- Author: Yuchen Pei (me@ypei.me)
import Numeric (showIntAtBase)
import Data.Char (intToDigit)
import Data.Map (Map)
import qualified Data.Map as Map
import Data.List.Split (splitOn, splitOneOf)
import System.Environment (getArgs)
parseLine :: Map [Char] [Char] -> [Char] -> [Char]
parseLine table (x:xs)
| x == '@' && (head xs `elem` ['0'..'9']) = (int2Bin16 $ read xs)
| x == '@' = table Map.! xs
| '=' `elem` (x:xs) && ';' `elem` (x:xs) = let [dest, comp, jump] = splitOneOf "=;" (x:xs) in "111" ++ (parseComp comp) ++ (parseDest dest) ++ (parseJump jump)
| '=' `elem` (x:xs) = let [dest, comp] = splitOn "=" (x:xs) in "111" ++ (parseComp comp) ++ (parseDest dest) ++ "000"
| ';' `elem` (x:xs) = let [comp, jump] = splitOn ";" (x:xs) in "111" ++ (parseComp comp) ++ "000" ++ (parseJump jump)
parseComp xs = case xs of
"0" -> "0101010"
"1" -> "0111111"
"-1" -> "0111010"
"D" -> "0001100"
"A" -> "0110000"
"!D" -> "0001101"
"!A" -> "0110001"
"-D" -> "0001111"
"-A" -> "0110011"
"D+1" -> "0011111"
"A+1" -> "0110111"
"D-1" -> "0001110"
"A-1" -> "0110010"
"D+A" -> "0000010"
"A+D" -> "0000010"
"D-A" -> "0010011"
"A-D" -> "0000111"
"D&A" -> "0000000"
"A&D" -> "0000000"
"D|A" -> "0010101"
"A|D" -> "0010101"
"M" -> "1110000"
"!M" -> "1110001"
"-M" -> "1110011"
"M+1" -> "1110111"
"M-1" -> "1110010"
"D+M" -> "1000010"
"M+D" -> "1000010"
"D-M" -> "1010011"
"M-D" -> "1000111"
"D&M" -> "1000000"
"M&D" -> "1000000"
"D|M" -> "1010101"
"M|D" -> "1010101"
parseDest xs = (f 'A'):(f 'D'):(f 'M'):[]
where f x = if x `elem` xs then '1' else '0'
parseJump xs = case xs of
"" -> "000"
"JGT" -> "001"
"JEQ" -> "010"
"JGE" -> "011"
"JLT" -> "100"
"JNE" -> "101"
"JLE" -> "110"
"JMP" -> "111"
int2Bin x = showIntAtBase 2 intToDigit x ""
int2Bin16 :: Int -> [Char]
int2Bin16 x = let xs = int2Bin x in replicate (16 - length xs) '0' ++ xs
initTable :: Map [Char] [Char]
initTable = Map.fromList $ (\(x, y) -> (x, int2Bin16 y)) <$> ("SP", 0):("LCL", 1):("ARG", 2):("THIS", 3):("THAT", 4):("SCREEN", 16384):("KBD", 24576):rs
where rs = zipWith (,) ((\x -> 'R':(show x)) <$> [0..15]) [0..15]
stripJunk :: [Char] -> [[Char]]
stripJunk xs = filter (not . null) $ (filter (not . (flip elem " \t")) . head . (splitOn "//")) <$> lines (replCrWithNl xs)
stripLabels :: [[Char]] -> [[Char]]
stripLabels = filter (not . (elem '('))
-- For labels
addLabels :: [[Char]] -> Int -> Map [Char] [Char] -> Map [Char] [Char]
addLabels [] _ table = table
addLabels ((hd:tl):rest) addr table
| hd == '(' = addLabels rest addr (Map.insert (init tl) (int2Bin16 addr) table)
| otherwise = addLabels rest (addr + 1) table
-- For variables, addr is the current instruction address, vaddr is the
-- variable memory address (to be assigned)
addSyms :: [[Char]] -> Int -> Int -> Map [Char] [Char] -> Map [Char] [Char]
addSyms [] _ _ table = table
addSyms ((hd:tl):rest) addr vaddr table
| hd == '(' = addSyms rest addr vaddr (Map.insert (init tl) (int2Bin16 addr) table)
| hd == '@' && head tl `notElem` ['0'..'9'] && tl `Map.notMember` table = addSyms rest (addr + 1) (vaddr + 1) (Map.insert tl (int2Bin16 vaddr) table)
| otherwise = addSyms rest (addr + 1) vaddr table
parseCode :: [Char] -> [Char]
parseCode code = unlines $ parseLine (addSyms codeWithoutLabels 0 16 (addLabels codeWithoutJunk 0 initTable)) <$> codeWithoutLabels
where codeWithoutJunk = stripJunk code
codeWithoutLabels = stripLabels codeWithoutJunk
replCrWithNl = fmap cr2nl
where cr2nl '\r' = '\n'
cr2nl c = c
main = do
args <- getArgs
let filename = head args
code <- readFile $ filename
writeFile (head (splitOn "." filename) ++ ".hack") (parseCode code)
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