Hi all, I recently started writing a simulator for Knuth's MIX computer in Haskell. My first attempt had the basic data types for the machine defined like this: type Byte = Word8 type Address = Word16 type Word = Word32 type FieldSpec = (Int,Int) data Register = A Word | X Word | I Address | J Address type Memory = M.Map Address Word After hitting some kind of dead end with this setup (basically getting frustrated/lost with all the bit-twiddling), I tried again with these more abstract types: data Byte = Byte Word8 data Sign = Plus | Minus data Address = Address Byte Byte data SignedAddress = SignedAddress Sign Address data Word = Word Sign Byte Byte Byte Byte Byte data FieldSpec = FieldSpec Int Int data Memory = Memory (M.Map Address Word) Now I find my code is much clearer (it almost writes itself...) and practically absent of low-level bit operations (except, for example, converting a Word into an actual Haskell Int32 to perform the actual arithmetic). However, I'm wondering about the cost of all the "packing/unpacking" via pattern-matching and/or accessors. Perhaps I should not worry about this and optimize later if required? Is this type of premature optimization (assuming the previous version was faster...) really the root of all evil? Note: I'm not far enough into the simulator to be able to actually test it out and get metrics. Patrick Thanks, Patrick -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada