Humza Shahid
6b91d64fc3
git-subtree-dir: shf git-subtree-mainline:401408448fgit-subtree-split:b6c5a95b66
77 lines
2.2 KiB
Standard ML
77 lines
2.2 KiB
Standard ML
structure ViHDfa =
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struct
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val startState: Word8.word = 0w0
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val oneNewlineState: Word8.word = 0w1
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val twoNewlineState: Word8.word = 0w2
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val chrState: Word8.word = 0w3
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val chrBeforeNewlieState: Word8.word = 0w4
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fun makeStart i =
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if Char.chr i = #"\n" then oneNewlineState else chrState
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fun makeOneNewline i =
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if Char.chr i = #"\n" then twoNewlineState else chrBeforeNewlieState
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val startTable = Vector.tabulate (255, makeStart)
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val oneNewlineTable = Vector.tabulate (255, makeOneNewline)
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val twoNewlineTable = oneNewlineTable
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val chrTable = startTable
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val chrBeforeNewlieTable = startTable
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val tables =
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#[ startTable
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, oneNewlineTable
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, twoNewlineTable
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, chrTable
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, chrBeforeNewlieTable
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]
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fun next (currentState, chr) =
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let val table = Vector.sub (tables, Word8.toInt currentState)
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in Vector.sub (table, Char.ord chr)
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end
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structure ViH =
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MakePrevDfaLoop
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(struct
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val startState = startState
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fun loop (idx, absIdx, str, tl, currentState, counter) =
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if idx < 0 then
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case tl of
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str :: tl =>
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loop
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(String.size str - 1, absIdx, str, tl, currentState, counter)
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| [] => 0
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else
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let
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val chr = String.sub (str, idx)
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val newState = next (currentState, chr)
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in
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if newState = chrBeforeNewlieState orelse newState = chrState then
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if counter - 1 = ~1 then
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absIdx
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else
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loop (idx - 1, absIdx - 1, str, tl, startState, counter - 1)
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else if newState = twoNewlineState then
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if counter - 1 = ~1 then
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absIdx + 1
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else
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loop
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( idx - 1
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, absIdx - 1
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, str
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, tl
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, oneNewlineState
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, counter - 1
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)
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else
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loop (idx - 1, absIdx - 1, str, tl, newState, counter)
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end
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val fStart = loop
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end)
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val prev = ViH.prev
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end
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