diff --git a/LexOccam.x b/LexOccam.x
new file mode 100644
index 0000000..b5e2974
--- /dev/null
+++ b/LexOccam.x
@@ -0,0 +1,149 @@
+{ {-
+Tock: a compiler for parallel languages
+Copyright (C) 2007  University of Kent
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation, either version 2 of the License, or (at your
+option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License along
+with this program.  If not, see <http://www.gnu.org/licenses/>.
+-}
+
+-- | Lexically analyse occam code.
+module LexOccam where
+
+import Data.Generics
+import System
+
+import Metadata
+import PrettyShow
+}
+
+%wrapper "posn"
+
+$decimalDigit = [0-9]
+$hexDigit = [0-9 a-f A-F]
+
+@reserved = "[" | "]" | "(" | ")"
+          | "::" | ":=" | ":" | "," | ";" | "&"
+          | "?" | "!" | "="
+          | "\" | "/\" | "\/"
+          | "+" | "-" | "*" | "/"
+          | "><" | "<<" | ">>" | "<>"
+          | ">=" | "<="
+          | "<" | ">"
+          | "~"
+          | "AFTER" | "ALT" | "AND" | "ANY" | "AT"
+          | "BITAND" | "BITNOT" | "BITOR" | "BOOL" | "BYTE" | "BYTESIN"
+          | "CASE" | "CHAN"
+          | "DATA"
+          | "ELSE"
+          | "FALSE" | "FOR" | "FROM" | "FUNCTION"
+          | "IF" | "IN" | "INLINE" | "INT" | "INT16" | "INT32" | "INT64"
+          | "IS"
+          | "MINUS" | "MOSTNEG" | "MOSTPOS"
+          | "NOT"
+          | "OF" | "OFFSETOF" | "OR"
+          | "PACKED" | "PAR" | "PLACE" | "PLACED" | "PLUS" | "PORT"
+          | "PRI" | "PROC" | "PROCESSOR" | "PROTOCOL"
+          | "REAL32" | "REAL64" | "RECORD" | "REM" | "RESHAPES"
+          | "RESULT" | "RETYPES" | "ROUND"
+          | "SEQ" | "SIZE" | "SKIP" | "STOP"
+          | "TIMER" | "TIMES" | "TRUE" | "TRUNC" | "TYPE"
+          | "VAL" | "VALOF"
+          | "WHILE" | "WORKSPACE"
+          | "VECSPACE"
+          | "#INCLUDE" | "#USE"
+
+@identifier = [a-z A-Z] [a-z A-Z 0-9 \.]*
+
+$escapeChar = [cnrts \" \' \* \n]
+@escape = \* ( $escapeChar | \# $hexDigit $hexDigit )
+
+@stringLiteral = \" ( @escape | [^\"] )* \"
+@charLiteral = \' ( @escape | [^\'] ) \'
+
+-- Note that occam number literals don't include their signs -- if you say
+-- "-3", then that's the operator "-" applied to the literal "3".
+@decimalLiteral = $decimalDigit+
+@hexLiteral = "#" $hexDigit+
+@exponent = ("+" | "-") $decimalDigit+
+@realLiteral = ( $decimalDigit+ "." $decimalDigit+ "E" @exponent )
+             | ( $decimalDigit+ "." $decimalDigit+ )
+
+occam :-
+
+-- Ignore whitespace and comments.
+$white+            ;
+"--" [^\n]*        ;
+
+@reserved          { mkToken TokReserved }
+@identifier        { mkToken TokIdentifier }
+
+@stringLiteral     { mkToken TokStringLiteral }
+@charLiteral       { mkToken TokCharLiteral }
+
+@decimalLiteral    { mkToken TokDecimalLiteral }
+@hexLiteral        { mkToken TokHexLiteral }
+@realLiteral       { mkToken TokRealLiteral }
+
+{
+-- | An occam source token.
+data Token = Token TokenType Meta String
+  deriving (Show, Eq, Typeable, Data)
+
+-- | The type of a source token.
+data TokenType =
+  TokReserved | TokIdentifier
+  | TokStringLiteral | TokCharLiteral
+  | TokDecimalLiteral | TokHexLiteral | TokRealLiteral
+  deriving (Show, Eq, Typeable, Data)
+
+-- | Build a lexer rule for a token.
+mkToken :: TokenType -> AlexPosn -> String -> Token
+mkToken tt (AlexPn _ line col) s = Token tt emptyMeta s
+
+-- | Run the lexer, returning either an error position or a list of tokens.
+-- (This is based on the `alexScanTokens` function that Alex provides, but it
+-- adds error reporting.)
+runLexer :: String -> String -> Either Meta [Token]
+runLexer filename str = go (alexStartPos, '\n', str)
+  where
+    go inp@(pos@(AlexPn _ line col), _, str) =
+         case alexScan inp 0 of
+           AlexEOF -> Right []
+           AlexError _ -> Left meta
+           AlexSkip inp' len -> go inp'
+           AlexToken inp' len act ->
+             case go inp' of
+               e@(Left _) -> e
+               Right ts -> Right $ tok : ts
+                             where (Token tt _ s) = act pos (take len str)
+                                   tok = Token tt meta s
+
+      where
+        meta = emptyMeta {
+                 metaFile = Just filename,
+                 metaLine = line,
+                 metaColumn = col
+               }
+
+-- | Main function for testing the lexer.
+main :: IO ()
+main
+    =  do (arg:_) <- getArgs
+          s <- readFile arg
+          let tokens =
+                case runLexer arg s of
+                  Left m -> error $ "Lex error: " ++ show m
+                  Right ts -> ts
+          putStrLn $ pshow tokens
+}
+
diff --git a/Makefile b/Makefile
index dec9656..5394140 100644
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,11 @@
-targets = tock tocktest
+targets = tock tocktest lextest
 
 all: $(targets)
 
-sources = $(wildcard *.hs)
+sources = $(wildcard *.hs) $(patsubst %.x,%.hs,$(wildcard *.x))
+
+%.hs: %.x
+	alex $<
 
 # profile_opts = -prof -auto-all
 ghc_opts = \
@@ -17,6 +20,9 @@ tock: $(sources)
 tocktest: $(sources)
 	ghc $(ghc_opts) -o tocktest -main-is TestMain --make TestMain
 
+lextest: $(sources)
+	ghc $(ghc_opts) -o lextest -main-is LexOccam --make LexOccam
+
 CFLAGS = \
 	-O2 \
 	-g -Wall \