GADTs in the wild

[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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/glasgow-haskell-users/attachments/20120823/cdf72524/attachment.htm>