-- Communicating Haskell Processes.
-- Copyright (c) 2008, University of Kent.
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module Control.Concurrent.CHP.ProcessId where

-- We derive Ord for these two types so that they can be used in sets.  However,
-- the Ord instance should not be confused with the partial ordering detailed
-- in the tracing paper, which is provided by the pidLessThanOrEqual function
-- below.

data ProcessIdPart = ParSeq Int Integer deriving (Eq, Ord, Show)

newtype ProcessId = ProcessId [ProcessIdPart] deriving (Eq, Ord, Show)

rootProcessId :: ProcessId
rootProcessId = ProcessId [ParSeq 0 0]

emptyProcessId :: ProcessId
emptyProcessId = ProcessId []

testProcessId :: Int -> ProcessId
testProcessId n = ProcessId [ParSeq n 0]

-- We use here the property that the lists will either be equal, or different
-- within their shared length.  Therefore they will be different when zipped,
-- or if they're identical that means the originals were identical
pidLessThanOrEqual :: ProcessId -> ProcessId -> Bool
pidLessThanOrEqual (ProcessId pida) (ProcessId pidb) = cmp (zip pida pidb)
    where
      cmp :: ([(ProcessIdPart, ProcessIdPart)]) -> Bool
      cmp [] = True -- Equal
      cmp ((ParSeq pa sa, ParSeq pb sb):xs)
        | pa /= pb  = False -- No ordering
        | sa < sb   = True -- Less than
        | sa > sb   = False -- Greater than
        | otherwise = cmp xs --Both parts equal, keep going