Probably useful to include a "mkFixed" function example as well, to show
how a Fixed can be constructed using the "optimal" data representation:
-- | Make a fixed field.
--
-- Note that this type constructor function chooses the minimal type
-- representation for the fixed value stored. Unsigned representations
-- are preferred over signed.
mkFixed :: String -> Int -> Integer -> Member
mkFixed name len val
| len <= 0 = error $ "mkFixed " ++ name ++ ": length < 0"
| len < 8 && validUnsigned len val = Fixed name len False (fromIntegral
val :: Word8)
| len < 8 && validSigned len val = Fixed name len True (fromIntegral
val :: Int8)
| len < 16 && validUnsigned len val = Fixed name len False (fromIntegral
val :: Word16)
| len < 16 && validSigned len val = Fixed name len True (fromIntegral
val :: Int16)
| len < 32 && validUnsigned len val = Fixed name len False (fromIntegral
val :: Word32)
| len < 32 && validSigned len val = Fixed name len True (fromIntegral
val :: Int32)
| len < 64 && validUnsigned len val = Fixed name len False (fromIntegral
val :: Word64)
| len < 64 && validSigned len val = Fixed name len True (fromIntegral
val :: Int64)
| otherwise = error $ "mkFixed " ++ name ++ ": cannot represent this bit
field"
On Thu, Aug 23, 2012 at 11:47 AM, Scott Michel
Here's an example (not a complete module) I was using to represent bit-oriented structures as they occur in certain space applications, notably GPS frames. "Fixed" allows for fixed-sized fields and lets the end user choose the integral type that's best for the structure.
At least it's not a parser or language example. :-)
-scooter
-- | Member fields, etc., that comprise a 'BitStruct' data Member where Field :: String -- Field name -> Int -- Field length -> Bool -- Signed (True) or unsigned (False) -> Member ZeroPad :: String -- Field name -> Int -- Field length -> Member OnesPad :: String -- Field name -> Int -- Field length -> Member ArbPad :: String -- Field name -> Int -- Field length -> Member Reserved :: String -- Field name -> Int -- Field length -> Member Fixed :: (Integral x, Show x) => String -- Field name -> Int -- Field length -> Bool -- Signed (True) or unsigned (False) -> x -- Type of the fixed field's value -> Member Variant :: (Integral x, Show x) => String -- Variant prefix name -> Maybe BitStruct -- Header before the tag -> TagElement -- The tag element itself -> Maybe BitStruct -- Common elements after the tag -> Seq (x, BitStruct) -- Variant element tuples (value, structure) -> Member -- Mult-value variant: Use this when multiple variant tag values have the -- same structure: MultiValueVariant :: (Integral x, Show x) => String -- Variant prefix name -> Maybe BitStruct -- Header before the tag -> TagElement -- The tag element itself -> Maybe BitStruct -- Common elements after the tag -> Seq ([x], BitStruct) -- Variant element tuples ([values], structure) -> Member