83 lines
2.1 KiB
Standard ML
83 lines
2.1 KiB
Standard ML
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structure PersistentVector =
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struct
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(* Clojure-style persistent vector,
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* as intermediary data structure
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* for building search list *)
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datatype t =
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BRANCH of t vector
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| LEAF of int vector
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val maxSize = 32
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val empty = LEAF #[]
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datatype append_result = APPEND of t | UPDATE of t
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fun helpAppend (key, tree) =
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case tree of
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BRANCH nodes =>
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let
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val lastNode = Vector.sub (nodes, Vector.length nodes - 1)
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in
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case helpAppend (key, lastNode) of
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UPDATE newLast =>
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let
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val newNode = Vector.update
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(nodes, Vector.length nodes - 1, newLast)
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val newNode = BRANCH newNode
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in
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UPDATE newNode
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end
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| APPEND newVec =>
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if Vector.length nodes + 1 > maxSize then
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let val newNode = BRANCH #[newVec]
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in APPEND newNode
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end
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else
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let
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val newNodes = Vector.concat [nodes, #[newVec]]
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val newNodes = BRANCH newNodes
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in
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UPDATE newNodes
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end
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end
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| LEAF vec =>
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if Vector.length vec + 1 > maxSize then
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let val newNode = LEAF #[key]
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in APPEND newNode
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end
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else
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let
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val newNode = Vector.concat [vec, #[key]]
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val newNode = LEAF newNode
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in
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UPDATE newNode
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end
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fun append (key, tree) =
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case helpAppend (key, tree) of
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UPDATE t => t
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| APPEND newNode => BRANCH #[tree, newNode]
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fun branchToList (pos, nodes, acc) =
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if pos < 0 then
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acc
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else
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let
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val node = Vector.sub (nodes, pos)
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val acc = helpToVector (node, acc)
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in
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branchToList (pos - 1, nodes, acc)
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end
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and helpToVector (tree, acc) =
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case tree of
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BRANCH nodes => branchToList (Vector.length nodes - 1, nodes, acc)
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| LEAF vec => vec :: acc
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fun toVector tree =
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let val lst = helpToVector (tree, [])
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in Vector.concat lst
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end
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end
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