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Trie

Functional key-value hash maps.

This module provides an applicative (functional) hash map, called a trie. Notably, each operation produces a new trie rather than destructively updating an existing trie.

Those looking for a more familiar (imperative, object-oriented) hash map should consider TrieMap or HashMap instead.

The basic Trie operations consist of:

  • put - put a key-value into the trie, producing a new version.
  • get - get a key's value from the trie, or null if none.
  • remove - remove a key's value from the trie
  • iter - visit every key-value in the trie.

The put, get and remove operations work over Key records, which group the hash of the key with its non-hash key value.

LIMITATIONS: This data structure allows at most MAX_LEAF_SIZE=8 hash collisions: attempts to insert more than MAX_LEAF_SIZE keys (whether directly via put or indirectly via other operations) with the same hash value will trap.

CREDITS: Based on Section 6 of "Incremental computation via function caching", Pugh & Teitelbaum.

Example:

import Trie "mo:base/Trie";
import Text "mo:base/Text";

// we do this to have shorter type names and thus
// better readibility
type Trie<K, V> = Trie.Trie<K, V>;
type Key<K> = Trie.Key<K>;

// we have to provide `put`, `get` and `remove` with
// a record of type `Key<K> = { hash : Hash.Hash; key : K }`;
// thus we define the following function that takes a value of type `K`
// (in this case `Text`) and returns a `Key<K>` record.
func key(t: Text) : Key<Text> { { hash = Text.hash t; key = t } };

// we start off by creating an empty `Trie`
let t0 : Trie<Text, Nat> = Trie.empty();

// `put` requires 4 arguments:
// - the trie we want to insert the value into,
// - the key of the value we want to insert (note that we use the `key` function defined above),
// - a function that checks for equality of keys, and
// - the value we want to insert.
//
// When inserting a value, `put` returns a tuple of type `(Trie<K, V>, ?V)`.
// to get the new trie that contains the value,  we use the `0` projection
// and assign it to `t1` and `t2` respectively.
let t1 : Trie<Text, Nat> = Trie.put(t0, key "hello", Text.equal, 42).0;
let t2 : Trie<Text, Nat> = Trie.put(t1, key "world", Text.equal, 24).0;

// If for a given key there already was a value in the trie, `put` returns
// that previous value as the second element of the tuple.
// in our case we have already inserted the value 42 for the key "hello", so
// `put` returns 42 as the second element of the tuple.
let (t3, n) : (Trie<Text, Nat>, ?Nat) = Trie.put(
  t2,
  key "hello",
  Text.equal,
  0,
);
assert (n == ?42);

// `get` requires 3 arguments:
// - the trie we want to get the value from
// - the key of the value we want to get (note that we use the `key` function defined above)
// - a function that checks for equality of keys
//
// If the given key is nonexistent in the trie, `get` returns `null`.
var value = Trie.get(t3, key "hello", Text.equal); // Returns `?42`
assert(value == ?0);
value := Trie.get(t3, key "universe", Text.equal); // Returns `null`
assert(value == null);

// `remove` requires 3 arguments:
// - the trie we want to remove the value from,
// - the key of the value we want to remove (note that we use the `key` function defined above), and
// - a function that checks for equality of keys.
//
// In the case of keys of type `Text`, we can use `Text.equal`
// to check for equality of keys. Function `remove` returns a tuple of type `(Trie<K, V>, ?V)`.
// where the second element of the tuple is the value that was removed, or `null` if
// there was no value for the given key.
let removedValue : ?Nat = Trie.remove(
  t3,
  key "hello",
  Text.equal,
).1;
assert (removedValue == ?0);

// To iterate over the Trie, we use the `iter` function that takes a trie
// of type `Trie<K,V>` and returns an iterator of type `Iter<(K,V)>`:
var sum : Nat = 0;
for (kv in Trie.iter(t3)) {
  sum += kv.1;
};
assert(sum == 24);

Type Trie​

type Trie<K, V> = {#empty; #leaf : Leaf<K, V>; #branch : Branch<K, V>}

Binary hash tries: either empty, a leaf node, or a branch node

Type Leaf​

type Leaf<K, V> = { size : Nat; keyvals : AssocList<Key<K>, V> }

Leaf nodes of trie consist of key-value pairs as a list.

Type Branch​

type Branch<K, V> = { size : Nat; left : Trie<K, V>; right : Trie<K, V> }

Branch nodes of the trie discriminate on a bit position of the keys' hashes. This bit position is not stored in the branch but determined from the context of the branch.

Type AssocList​

type AssocList<K, V> = AssocList.AssocList<K, V>

Type Key​

type Key<K> = { hash : Hash.Hash; key : K }

A Key for the trie has an associated hash value

  • hash permits fast inequality checks, and permits collisions, while
  • key permits precise equality checks, but is only used on values with equal hashes.

Function equalKey​

func equalKey<K>(keq : (K, K) -> Bool) : ((Key<K>, Key<K>) -> Bool)

Equality function for two Key<K>s, in terms of equality of K's.

Function isValid​

func isValid<K, V>(t : Trie<K, V>, _enforceNormal : Bool) : Bool

@deprecated isValid is an internal predicate and will be removed in future.

Type Trie2D​

type Trie2D<K1, K2, V> = Trie<K1, Trie<K2, V>>

A 2D trie maps dimension-1 keys to another layer of tries, each keyed on the dimension-2 keys.

Type Trie3D​

type Trie3D<K1, K2, K3, V> = Trie<K1, Trie2D<K2, K3, V>>

A 3D trie maps dimension-1 keys to another Composition of 2D tries, each keyed on the dimension-2 and dimension-3 keys.

Function empty​

func empty<K, V>() : Trie<K, V>

An empty trie. This is usually the starting point for building a trie.

Example:

import { print } "mo:base/Debug";
import Trie "mo:base/Trie";
import Text "mo:base/Text";

// we do this to have shorter type names and thus
// better readibility
type Trie<K, V> = Trie.Trie<K, V>;
type Key<K> = Trie.Key<K>;

// We have to provide `put`, `get` and `remove` with
// a function of return type `Key<K> = { hash : Hash.Hash; key : K }`
func key(t: Text) : Key<Text> { { hash = Text.hash t; key = t } };
// We start off by creating an empty `Trie`
var trie : Trie<Text, Nat> = Trie.empty();

Function size​

func size<K, V>(t : Trie<K, V>) : Nat

Get the size in O(1) time.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

var size = Trie.size(trie); // Returns 0, as `trie` is empty
assert(size == 0);
trie := Trie.put(trie, key "hello", Text.equal, 42).0;
size := Trie.size(trie); // Returns 1, as we just added a new entry
assert(size == 1);

Function branch​

func branch<K, V>(l : Trie<K, V>, r : Trie<K, V>) : Trie<K, V>

Construct a branch node, computing the size stored there.

Function leaf​

func leaf<K, V>(kvs : AssocList<Key<K>, V>, bitpos : Nat) : Trie<K, V>

Construct a leaf node, computing the size stored there.

This helper function automatically enforces the MAX_LEAF_SIZE by constructing branches as necessary; to do so, it also needs the bitpos of the leaf.

Function fromList​

func fromList<K, V>(kvc : ?Nat, kvs : AssocList<Key<K>, V>, bitpos : Nat) : Trie<K, V>

Transform a list into a trie, splitting input list into small (leaf) lists, if necessary.

Function clone​

func clone<K, V>(t : Trie<K, V>) : Trie<K, V>

Clone the trie efficiently, via sharing.

Purely-functional representation permits O(1) copy, via persistent sharing.

Function replace​

func replace<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool, v : ?V) : (Trie<K, V>, ?V)

Replace the given key's value option with the given value, returning the modified trie. Also returns the replaced value if the key existed and null otherwise. Compares keys using the provided function k_eq.

Note: Replacing a key's value by null removes the key and also shrinks the trie.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "test", Text.equal, 1).0;
trie := Trie.replace(trie, key "test", Text.equal, 42).0;
assert (Trie.get(trie, key "hello", Text.equal) == ?42);

Function put​

func put<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool, v : V) : (Trie<K, V>, ?V)

Put the given key's value in the trie; return the new trie, and the previous value associated with the key, if any.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
let previousValue = Trie.put(trie, key "hello", Text.equal, 33).1; // Returns ?42
assert(previousValue == ?42);

Function get​

func get<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool) : ?V

Get the value of the given key in the trie, or return null if nonexistent.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
var value = Trie.get(trie, key "hello", Text.equal); // Returns `?42`
assert(value == ?42);
value := Trie.get(trie, key "world", Text.equal); // Returns `null`
assert(value == null);

Function find​

func find<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool) : ?V

Find the given key's value in the trie, or return null if nonexistent

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
var value = Trie.find(trie, key "hello", Text.equal); // Returns `?42`
assert(value == ?42);
value := Trie.find(trie, key "world", Text.equal); // Returns `null`
assert(value == null);

Function merge​

func merge<K, V>(tl : Trie<K, V>, tr : Trie<K, V>, k_eq : (K, K) -> Bool) : Trie<K, V>

Merge tries, preferring the left trie where there are collisions in common keys.

note: the disj operation generalizes this merge operation in various ways, and does not (in general) lose information; this operation is a simpler, special case.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 42).0;
// trie2 is a copy of trie
var trie2 = Trie.clone(trie);
// trie2 has a different value for "hello"
trie2 := Trie.put(trie2, key "hello", Text.equal, 33).0;
// mergedTrie has the value 42 for "hello", as the left trie is preferred
// in the case of a collision
var mergedTrie = Trie.merge(trie, trie2, Text.equal);
var value = Trie.get(mergedTrie, key "hello", Text.equal);
assert(value == ?42);

Function mergeDisjoint​

func mergeDisjoint<K, V>(tl : Trie<K, V>, tr : Trie<K, V>, k_eq : (K, K) -> Bool) : Trie<K, V>

Merge tries like merge, but traps if there are collisions in common keys between the left and right inputs.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 42).0;
// trie2 is a copy of trie
var trie2 = Trie.clone(trie);
// trie2 has a different value for "hello"
trie2 := Trie.put(trie2, key "hello", Text.equal, 33).0;
// `mergeDisjoint` signals a dynamic errror
// in the case of a collision
var mergedTrie = Trie.mergeDisjoint(trie, trie2, Text.equal);

Function diff​

func diff<K, V, W>(tl : Trie<K, V>, tr : Trie<K, W>, k_eq : (K, K) -> Bool) : Trie<K, V>

Difference of tries. The output consists of pairs of the left trie whose keys are not present in the right trie; the values of the right trie are irrelevant.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 42).0;
// trie2 is a copy of trie
var trie2 = Trie.clone(trie);
// trie2 now has an additional key
trie2 := Trie.put(trie2, key "ciao", Text.equal, 33).0;
// `diff` returns a trie with the key "ciao",
// as this key is not present in `trie`
// (note that we pass `trie2` as the left trie)
Trie.diff(trie2, trie, Text.equal);

Function disj​

func disj<K, V, W, X>(tl : Trie<K, V>, tr : Trie<K, W>, k_eq : (K, K) -> Bool, vbin : (?V, ?W) -> X) : Trie<K, X>

Map disjunction.

This operation generalizes the notion of "set union" to finite maps.

Produces a "disjunctive image" of the two tries, where the values of matching keys are combined with the given binary operator.

For unmatched key-value pairs, the operator is still applied to create the value in the image. To accomodate these various situations, the operator accepts optional values, but is never applied to (null, null).

Implements the database idea of an "outer join".

Function join​

func join<K, V, W, X>(tl : Trie<K, V>, tr : Trie<K, W>, k_eq : (K, K) -> Bool, vbin : (V, W) -> X) : Trie<K, X>

Map join.

Implements the database idea of an "inner join".

This operation generalizes the notion of "set intersection" to finite maps. The values of matching keys are combined with the given binary operator, and unmatched key-value pairs are not present in the output.

Function foldUp​

func foldUp<K, V, X>(t : Trie<K, V>, bin : (X, X) -> X, leaf : (K, V) -> X, empty : X) : X

This operation gives a recursor for the internal structure of tries. Many common operations are instantiations of this function, either as clients, or as hand-specialized versions (e.g., see , map, mapFilter, some and all below).

Function prod​

func prod<K1, V1, K2, V2, K3, V3>(tl : Trie<K1, V1>, tr : Trie<K2, V2>, op : (K1, V1, K2, V2) -> ?(Key<K3>, V3), k3_eq : (K3, K3) -> Bool) : Trie<K3, V3>

Map product.

Conditional catesian product, where the given operation op conditionally creates output elements in the resulting trie.

The keyed structure of the input tries are not relevant for this operation: all pairs are considered, regardless of keys matching or not. Moreover, the resulting trie may use keys that are unrelated to these input keys.

Function iter​

func iter<K, V>(t : Trie<K, V>) : I.Iter<(K, V)>

Returns an iterator of type Iter over the key-value entries of the trie.

Each iterator gets a persistent view of the mapping, independent of concurrent updates to the iterated map.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
// create an Iterator over key-value pairs of trie
let iter = Trie.iter(trie);
// add another key-value pair to `trie`.
// because we created our iterator before
// this update, it will not contain this new key-value pair
trie := Trie.put(trie, key "ciao", Text.equal, 3).0;
var sum : Nat = 0;
for ((k,v) in iter) {
  sum += v;
};
assert(sum == 74);

Module Build​

module Build

Represent the construction of tries as data.

This module provides optimized variants of normal tries, for more efficient join queries.

The central insight is that for (unmaterialized) join query results, we do not need to actually build any resulting trie of the resulting data, but rather, just need a collection of what would be in that trie. Since query results can be large (quadratic in the DB size), avoiding the construction of this trie provides a considerable savings.

To get this savings, we use an ADT for the operations that would build this trie, if evaluated. This structure specializes a rope: a balanced tree representing a sequence. It is only as balanced as the tries from which we generate these build ASTs. They have no intrinsic balance properties of their own.

Type Build​

type Build<K, V> = {#skip; #put : (K, ?Hash.Hash, V); #seq : { size : Nat; left : Build<K, V>; right : Build<K, V> }}

The build of a trie, as an AST for a simple DSL.

Function size​

func size<K, V>(tb : Build<K, V>) : Nat

Size of the build, measured in #put operations

Function seq​

func seq<K, V>(l : Build<K, V>, r : Build<K, V>) : Build<K, V>

Build sequence of two sub-builds

Function prod​

func prod<K1, V1, K2, V2, K3, V3>(tl : Trie<K1, V1>, tr : Trie<K2, V2>, op : (K1, V1, K2, V2) -> ?(K3, V3), _k3_eq : (K3, K3) -> Bool) : Build<K3, V3>

Like prod, except do not actually do the put calls, just record them, as a (binary tree) data structure, isomorphic to the recursion of this function (which is balanced, in expectation).

Function nth​

func nth<K, V>(tb : Build<K, V>, i : Nat) : ?(K, ?Hash.Hash, V)

Project the nth key-value pair from the trie build.

This position is meaningful only when the build contains multiple uses of one or more keys, otherwise it is not.

Function projectInner​

func projectInner<K1, K2, V>(t : Trie<K1, Build<K2, V>>) : Build<K2, V>

Like mergeDisjoint, except that it avoids the work of actually merging any tries; rather, just record the work for latter (if ever).

Function toArray​

func toArray<K, V, W>(tb : Build<K, V>, f : (K, V) -> W) : [W]

Gather the collection of key-value pairs into an array of a (possibly-distinct) type.

Function fold​

func fold<K, V, X>(t : Trie<K, V>, f : (K, V, X) -> X, x : X) : X

Fold over the key-value pairs of the trie, using an accumulator. The key-value pairs have no reliable or meaningful ordering.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 3).0;
// create an accumulator, in our case the sum of all values
func calculateSum(k : Text, v : Nat, acc : Nat) : Nat = acc + v;
// Fold over the trie using the accumulator.
// Note that 0 is the initial value of the accumulator.
let sum = Trie.fold(trie, calculateSum, 0);
assert(sum == 77);

Function some​

func some<K, V>(t : Trie<K, V>, f : (K, V) -> Bool) : Bool

Test whether a given key-value pair is present, or not.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 3).0;
// `some` takes a function that returns a Boolean indicating whether
// the key-value pair is present or not
var isPresent = Trie.some(
  trie,
  func(k : Text, v : Nat) : Bool = k == "bye" and v == 32,
);
assert(isPresent == true);
isPresent := Trie.some(
  trie,
  func(k : Text, v : Nat) : Bool = k == "hello" and v == 32,
);
assert(isPresent == false);

Function all​

func all<K, V>(t : Trie<K, V>, f : (K, V) -> Bool) : Bool

Test whether all key-value pairs have a given property.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `all` takes a function that returns a boolean indicating whether
// the key-value pairs all have a given property, in our case that
// all values are greater than 9
var hasProperty = Trie.all(
  trie,
  func(k : Text, v : Nat) : Bool = v > 9,
);
assert(hasProperty == true);
// now we check if all values are greater than 100
hasProperty := Trie.all(
  trie,
  func(k : Text, v : Nat) : Bool = v > 100,
);
assert(hasProperty == false);

Function nth​

func nth<K, V>(t : Trie<K, V>, i : Nat) : ?(Key<K>, V)

Project the nth key-value pair from the trie.

Note: This position is not meaningful; it's only here so that we can inject tries into arrays using functions like Array.tabulate.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

import Array "mo:base/Array";
trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `tabulate` takes a size parameter, so we check the size of
// the trie first
let size = Trie.size(trie);
// Now we can create an array of the same size passing `nth` as
// the generator used to fill the array.
// Note that `toArray` is a convenience function that does the
// same thing without you having to check whether the tuple is
// `null` or not, which we're not doing in this example
let array = Array.tabulate<?(Key<Text>, Nat)>(
  size,
  func n = Trie.nth(trie, n)
);

Function toArray​

func toArray<K, V, W>(t : Trie<K, V>, f : (K, V) -> W) : [W]

Gather the collection of key-value pairs into an array of a (possibly-distinct) type.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `toArray` takes a function that takes a key-value tuple
// and returns a value of the type you want to use to fill
// the array.
// In our case we just return the value
let array = Trie.toArray<Text, Nat, Nat>(
  trie,
  func (k, v) = v
);

Function isEmpty​

func isEmpty<K, V>(t : Trie<K, V>) : Bool

Test for "deep emptiness": subtrees that have branching structure, but no leaves. These can result from naive filtering operations; filter uses this function to avoid creating such subtrees.

Function filter​

func filter<K, V>(t : Trie<K, V>, f : (K, V) -> Bool) : Trie<K, V>

Filter the key-value pairs by a given predicate.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `filter` takes a function that takes a key-value tuple
// and returns true if the key-value pair should be included.
// In our case those are pairs with a value greater than 20
let filteredTrie = Trie.filter<Text, Nat>(
  trie,
  func (k, v) = v > 20
);
assert (Trie.all<Text, Nat>(filteredTrie, func(k, v) = v > 20) == true);

Function mapFilter​

func mapFilter<K, V, W>(t : Trie<K, V>, f : (K, V) -> ?W) : Trie<K, W>

Map and filter the key-value pairs by a given predicate.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `mapFilter` takes a function that takes a key-value tuple
// and returns a possibly-distinct value if the key-value pair should be included.
// In our case, we filter for values greater than 20 and map them to their square.
let filteredTrie = Trie.mapFilter<Text, Nat, Nat>(
  trie,
  func (k, v) = if (v > 20) return ?(v**2) else return null
);
assert (Trie.all<Text, Nat>(filteredTrie, func(k, v) = v > 60) == true);

Function equalStructure​

func equalStructure<K, V>(tl : Trie<K, V>, tr : Trie<K, V>, keq : (K, K) -> Bool, veq : (V, V) -> Bool) : Bool

Test for equality, but naively, based on structure. Does not attempt to remove "junk" in the tree; For instance, a "smarter" approach would equate #bin {left = #empty; right = #empty} with #empty. We do not observe that equality here.

Function replaceThen​

func replaceThen<K, V, X>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool, v2 : V, success : (Trie<K, V>, V) -> X, fail : () -> X) : X

Replace the given key's value in the trie, and only if successful, do the success continuation, otherwise, return the failure value

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
trie := Trie.put(trie, key "ciao", Text.equal, 10).0;
// `replaceThen` takes the same arguments as `replace` but also a success continuation
// and a failure connection that are called in the respective scenarios.
// if the replace fails, that is the key is not present in the trie, the failure continuation is called.
// if the replace succeeds, that is the key is present in the trie, the success continuation is called.
// in this example we are simply returning the Text values `success` and `fail` respectively.
var continuation = Trie.replaceThen<Text, Nat, Text>(
  trie,
  key "hello",
  Text.equal,
  12,
  func (t, v) = "success",
  func () = "fail"
);
assert (continuation == "success");
continuation := Trie.replaceThen<Text, Nat, Text>(
  trie,
  key "shalom",
  Text.equal,
  12,
  func (t, v) = "success",
  func () = "fail"
);
assert (continuation == "fail");

Function putFresh​

func putFresh<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool, v : V) : Trie<K, V>

Put the given key's value in the trie; return the new trie; assert that no prior value is associated with the key

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

// note that compared to `put`, `putFresh` does not return a tuple
trie := Trie.putFresh(trie, key "hello", Text.equal, 42);
trie := Trie.putFresh(trie, key "bye", Text.equal, 32);
// this will fail as "hello" is already present in the trie
trie := Trie.putFresh(trie, key "hello", Text.equal, 10);

Function put2D​

func put2D<K1, K2, V>(t : Trie2D<K1, K2, V>, k1 : Key<K1>, k1_eq : (K1, K1) -> Bool, k2 : Key<K2>, k2_eq : (K2, K2) -> Bool, v : V) : Trie2D<K1, K2, V>

Put the given key's value in the 2D trie; return the new 2D trie.

Function put3D​

func put3D<K1, K2, K3, V>(t : Trie3D<K1, K2, K3, V>, k1 : Key<K1>, k1_eq : (K1, K1) -> Bool, k2 : Key<K2>, k2_eq : (K2, K2) -> Bool, k3 : Key<K3>, k3_eq : (K3, K3) -> Bool, v : V) : Trie3D<K1, K2, K3, V>

Put the given key's value in the trie; return the new trie;

Function remove​

func remove<K, V>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool) : (Trie<K, V>, ?V)

Remove the entry for the given key from the trie, by returning the reduced trie. Also returns the removed value if the key existed and null otherwise. Compares keys using the provided function k_eq.

Note: The removal of an existing key shrinks the trie.

For a more detailed overview of how to use a Trie, see the User's Overview.

Example:

trie := Trie.put(trie, key "hello", Text.equal, 42).0;
trie := Trie.put(trie, key "bye", Text.equal, 32).0;
// remove the entry associated with "hello"
trie := Trie.remove(trie, key "hello", Text.equal).0;
assert (Trie.get(trie, key "hello", Text.equal) == null);

Function removeThen​

func removeThen<K, V, X>(t : Trie<K, V>, k : Key<K>, k_eq : (K, K) -> Bool, success : (Trie<K, V>, V) -> X, fail : () -> X) : X

Remove the given key's value in the trie, and only if successful, do the success continuation, otherwise, return the failure value

Function remove2D​

func remove2D<K1, K2, V>(t : Trie2D<K1, K2, V>, k1 : Key<K1>, k1_eq : (K1, K1) -> Bool, k2 : Key<K2>, k2_eq : (K2, K2) -> Bool) : (Trie2D<K1, K2, V>, ?V)

remove the given key-key pair's value in the 2D trie; return the new trie, and the prior value, if any.

Function remove3D​

func remove3D<K1, K2, K3, V>(t : Trie3D<K1, K2, K3, V>, k1 : Key<K1>, k1_eq : (K1, K1) -> Bool, k2 : Key<K2>, k2_eq : (K2, K2) -> Bool, k3 : Key<K3>, k3_eq : (K3, K3) -> Bool) : (Trie3D<K1, K2, K3, V>, ?V)

Remove the given key-key pair's value in the 3D trie; return the new trie, and the prior value, if any.

Function mergeDisjoint2D​

func mergeDisjoint2D<K1, K2, V>(t : Trie2D<K1, K2, V>, _k1_eq : (K1, K1) -> Bool, k2_eq : (K2, K2) -> Bool) : Trie<K2, V>

Like mergeDisjoint, except instead of merging a pair, it merges the collection of dimension-2 sub-trees of a 2D trie.