Parse assembly statements

This commit begins the rewrite of the assembly parser to use the new (not yet
written down) syntax.

src/Mima/Parse/Assembly/Directive.hs

@@ -0,0 +1,65 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Mima.Parse.Assembly.Directive
+  ( SetRegister(..)
+  , Directive(..)
+  , lDirective
+  ) where
+
+import qualified Data.Set as Set
+import           Text.Megaparsec
+
+import           Mima.Parse.Assembly.Common
+import           Mima.Parse.Assembly.Lexeme
+import           Mima.Parse.Common
+import           Mima.Word
+
+data SetRegister a
+  = SetIAR a
+  | SetACC MimaWord
+  | SetRA a
+  | SetSP a
+  | SetFP a
+  deriving (Show)
+
+data Directive a
+  = DReg (SetRegister a)    -- .reg (iar|acc|ra|sp|fp) <initial value>
+  | DOrg MimaAddress        -- .org <address>
+  | DLit MimaWord           -- .lit <word>
+  | DArr [MimaWord]         -- .arr [<word>, ...]
+  | DFlag (Set.Set Char)    -- .flag <chars>
+  | DFlagOn (Set.Set Char)  -- .flagon <chars>
+  | DFlagOff (Set.Set Char) -- .flagoff <chars>
+  deriving (Show)
+
+lSetRegister :: Parser (SetRegister Address)
+lSetRegister =
+      SetIAR <$> sepBySpace "iar" address
+  <|> SetACC <$> sepBySpace "acc" word
+  <|> SetRA  <$> sepBySpace "ra" address
+  <|> SetSP  <$> sepBySpace "sp" address
+  <|> SetFP  <$> sepBySpace "fp" address
+  where
+    sepBySpace name parser = symbol name *> lSpace *> lexeme parser
+
+lWordArray :: Parser [MimaWord]
+lWordArray = open *> (word `sepBy` comma) <* close
+  where
+    open  = lexeme $ symbol "["
+    comma = lexeme $ symbol ","
+    close = lexeme $ symbol "]"
+
+lFlags :: Parser (Set.Set Char)
+lFlags = Set.unions <$> some (lexeme flag)
+
+lDirective :: Parser (Directive Address)
+lDirective = label "assembler directive" $ undefined
+      DReg <$> directive ".reg" lSetRegister
+  <|> DOrg <$> directive ".org" (lexeme largeValue)
+  <|> DLit <$> directive ".lit" (lexeme word)
+  <|> DArr <$> directive ".arr" lWordArray
+  <|> DFlag    <$> directive ".flag"    lFlags
+  <|> DFlagOn  <$> directive ".flagon"  lFlags
+  <|> DFlagOff <$> directive ".flagoff" lFlags
+  where
+    directive name parser = symbol name *> lSpace *> parser