implement foldl, foldlWithPrefix, foldr and foldrWithPrefix
This commit is contained in:
46
README.md
46
README.md
@@ -6,6 +6,8 @@ The signature provided is:
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```
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signature STRING_SET =
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sig
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signature STRING_SET =
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sig
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(* the type of tries *)
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type t
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@@ -13,29 +15,55 @@ sig
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(* the empty trie *)
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val empty: t
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(* returns true if the trie is empty *)
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(* StringSet.isEmpty trie
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* returns true if the trie is empty *)
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val isEmpty: t -> bool
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(* creates a trie containing just a string *)
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(* StringSet.fromString "hello world"
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* creates a trie containing just a string *)
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val fromString: string -> t
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(* returns true if the key was inserted into the trie *)
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(* StringSet.exists ("hello world", trie)
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* returns true if the key was inserted into the trie *)
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val exists: string * t -> bool
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(* inserts a new string into the trie, returning a new trie *)
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(* StringSet.insert ("myNewString", trie)
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* inserts a new string into the trie, returning a new trie *)
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val insert: string * t -> t
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(* removes the key from the trie, returning a new trie *)
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(* StringSet.remove ("stringToRemove", trie)
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* removes the key from the trie, returning a new trie *)
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val remove: string * t -> t
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(* returns a list of all keys matching the specified prefix *)
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(* StringSet.getPrefixList ("myPrefix", trie)
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* returns a list of all keys matching the specified prefix *)
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val getPrefixList: string * t -> string list
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(* returns a list containing all keys in the trie *)
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(* StringSet.toList trie
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* returns a list containing all keys in the trie *)
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val toList: t -> string list
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(* returns a trie containing all keys in the string list *)
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(* StringSet.fromList ["hello", "world"]
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* returns a trie containing all keys in the string list *)
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val fromList: string list -> t
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(* StringSet.foldl (fn (key, acc) => String.size key + acc) 0 trie
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* folds a value through the trie, from lowest to highest. *)
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val foldl: (string * 'b -> 'b) -> 'b -> t -> 'b
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(* StringSet.foldlWithPrefix (fn (key, acc) => String.size key + acc) 0 trie "myPrefix"
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* folds a value through a subset of the trie containing the specified prefix,
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* from lowest to highest. *)
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val foldlWithPrefix: (string * 'b -> 'b) -> 'b -> t -> string -> 'b
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(* StringSet.foldr (fn (key, acc) => String.size key + acc) 0 trie
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* folds a value through the trie, from highest to lowest. *)
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val foldr: (string * 'b -> 'b) -> 'b -> t -> 'b
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(* StringSet.foldrWithPrefix (fn (key, acc) => String.size key + acc) 0 trie "myPrefix"
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* folds a value through a subset of the trie containing the specified prefix,
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* from highest to lowest. *)
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val foldrWithPrefix: (string * 'b -> 'b) -> 'b -> t -> string -> 'b
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end
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```
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@@ -43,7 +71,7 @@ The reason for implementing a new trie specialised to strings rather than using
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# To-do
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- [ ] Add `foldl`, `foldr`, `foldlWithPrefix`, `foldrWithPrefix` functions to string set
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- [x] Add `foldl`, `foldr`, `foldlWithPrefix`, `foldrWithPrefix` functions to string set
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- [ ] Benchmarks (possibly comparing to a set of strings in a balanced binary tree)
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- [ ] Use unrolled linked list with zipper in trie, to limit size of vector as allocating large vectors repeatedly is expensive
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- [ ] Implement StringMap, containing both keys and values
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@@ -6,29 +6,55 @@ sig
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(* the empty trie *)
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val empty: t
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(* returns true if the trie is empty *)
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(* StringSet.isEmpty trie
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* returns true if the trie is empty *)
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val isEmpty: t -> bool
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(* creates a trie containing just a string *)
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(* StringSet.fromString "hello world"
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* creates a trie containing just a string *)
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val fromString: string -> t
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(* returns true if the key was inserted into the trie *)
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(* StringSet.exists ("hello world", trie)
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* returns true if the key was inserted into the trie *)
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val exists: string * t -> bool
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(* inserts a new string into the trie, returning a new trie *)
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(* StringSet.insert ("myNewString", trie)
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* inserts a new string into the trie, returning a new trie *)
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val insert: string * t -> t
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(* removes the key from the trie, returning a new trie *)
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(* StringSet.remove ("stringToRemove", trie)
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* removes the key from the trie, returning a new trie *)
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val remove: string * t -> t
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(* returns a list of all keys matching the specified prefix *)
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(* StringSet.getPrefixList ("myPrefix", trie)
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* returns a list of all keys matching the specified prefix *)
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val getPrefixList: string * t -> string list
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(* returns a list containing all keys in the trie *)
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(* StringSet.toList trie
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* returns a list containing all keys in the trie *)
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val toList: t -> string list
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(* returns a trie containing all keys in the string list *)
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(* StringSet.fromList ["hello", "world"]
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* returns a trie containing all keys in the string list *)
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val fromList: string list -> t
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(* StringSet.foldl (fn (key, acc) => String.size key + acc) 0 trie
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* folds a value through the trie, from lowest to highest. *)
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val foldl: (string * 'b -> 'b) -> 'b -> t -> 'b
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(* StringSet.foldlWithPrefix (fn (key, acc) => String.size key + acc) 0 trie "myPrefix"
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* folds a value through a subset of the trie containing the specified prefix,
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* from lowest to highest. *)
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val foldlWithPrefix: (string * 'b -> 'b) -> 'b -> t -> string -> 'b
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(* StringSet.foldr (fn (key, acc) => String.size key + acc) 0 trie
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* folds a value through the trie, from highest to lowest. *)
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val foldr: (string * 'b -> 'b) -> 'b -> t -> 'b
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(* StringSet.foldrWithPrefix (fn (key, acc) => String.size key + acc) 0 trie "myPrefix"
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* folds a value through a subset of the trie containing the specified prefix,
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* from highest to lowest. *)
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val foldrWithPrefix: (string * 'b -> 'b) -> 'b -> t -> string -> 'b
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end
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structure StringSet: STRING_SET =
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@@ -227,6 +253,75 @@ struct
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else
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PREFIX_MATCHES_WHOLE_TRIE
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fun helpFoldlTrieVector (f, pos, keys, children, acc) =
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if pos = Vector.length children then
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acc
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else
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let
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val curChild = Vector.sub (children, pos)
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val acc = helpFoldl (f, curChild, acc)
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val acc =
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if isFoundNode curChild then f (Vector.sub (keys, pos), acc) else acc
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in
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helpFoldlTrieVector (f, pos + 1, keys, children, acc)
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end
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and helpFoldl (f, trie, acc) =
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case trie of
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CHILDREN {keys, children} =>
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helpFoldlTrieVector (f, 0, keys, children, acc)
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| FOUND_WITH_CHILDREN {keys, children} =>
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helpFoldlTrieVector (f, 0, keys, children, acc)
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| FOUND => acc
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fun foldl f initial trie = helpFoldl (f, trie, initial)
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fun foldlWithPrefix f initial trie prefix =
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case getPrefixSubtrie (prefix, trie) of
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PREFIX_FOUND (prefix, subtrie) =>
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let val acc = helpFoldl (f, subtrie, initial)
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in if isFoundNode subtrie then f (prefix, acc) else acc
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end
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| NO_PREFIX_FOUND => initial
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| PREFIX_MATCHES_WHOLE_TRIE => helpFoldl (f, trie, initial)
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fun helpFoldrTrieVector (f, pos, keys, children, 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 curChild = Vector.sub (children, pos)
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val acc = helpFoldr (f, curChild, acc)
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val acc =
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if isFoundNode curChild then f (Vector.sub (keys, pos), acc) else acc
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in
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helpFoldrTrieVector (f, pos - 1, keys, children, acc)
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end
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and helpFoldr (f, trie, acc) =
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case trie of
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CHILDREN {keys, children} =>
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helpFoldrTrieVector (f, Vector.length keys - 1, keys, children, acc)
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| FOUND_WITH_CHILDREN {keys, children} =>
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helpFoldrTrieVector (f, Vector.length keys - 1, keys, children, acc)
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| FOUND => acc
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fun foldr f initial trie = helpFoldr (f, trie, initial)
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fun foldrWithPrefix f initial trie prefix =
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case getPrefixSubtrie (prefix, trie) of
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PREFIX_FOUND (prefix, subtrie) =>
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let val acc = helpFoldr (f, subtrie, initial)
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in if isFoundNode subtrie then f (prefix, acc) else acc
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end
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| NO_PREFIX_FOUND => initial
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| PREFIX_MATCHES_WHOLE_TRIE => helpFoldr (f, trie, initial)
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(* recurseHelpGetPrefixList and helpGetPrefixList are basically manually coded
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* foldr functions over the trie, applying the accumuluator to every found
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* node, from right to left.
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* No need to recode it as a usage of a generic foldr function though,
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* because lower dispatch cost this way. *)
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fun recurseHelpGetPrefixList (pos, keys, children, acc) =
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if pos < 0 then
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acc
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@@ -568,10 +663,7 @@ struct
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end
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| fromList ([]) = empty
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datatype remove_result =
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UNCHANGED
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| MADE_EMPTY
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| CHANGED of t
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datatype remove_result = UNCHANGED | MADE_EMPTY | CHANGED of t
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(* should be called when there is a FULL_SEARCH_MATCH
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* and child is a terminal FOUND node *)
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