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Dict

This module provides functions for manipulating Dictionaries. Dictionaries are immutable data structure containing unique pairs of key and value.

Usage

There is a special syntax to create an empty dictionary: {}. Dictionaries support special operators for adding elements or operations typical for dictionaries, such as unions or intersections etc.

Folding a dictionary

Folding a dictionary is a process of iterating over its key-value pairs while producing one result value. An example of a folding function could be a sum function, that iterates over all elements and adds all the values up, producing a single result.

Functions foldl take 3 arguments: * dictionary to fold * 2-argument lambda (accumulator, (key, value)) returning a new value of an accumulator * initial value of the accumulator

This example shows how to sum up a dictionary:

Dict::fold {'a' = 1, 'b' = 2, 'c' = 3} (\acc (key, value) -> acc + value) 0

Reducing a dictionary

Reducing a dictionary means applying a transducer onto a dictionary. Transducers are a generic, high-level method for implementing operations over a data structure.

Function reduce takes 2 arguments: * dictionary to reduce * transducer

Example with a map transducer:

Dict::reduce {'a' = 1, 'b' = 2, 'c' = 3} <| Transducers::map \val -> val * 2 (0, \state val -> state + 1, identity)

This example will produce 12, as it sums up all the values doubled.

Obtaining a length of a dictionary

Function len returns a length of a dictionary:

length = Dict::len {'a' = 1, 'b' = 2, 'c' = 3}

Looking up a value by a key

Function lookup returns a value by the key, or () if not found.

First argument is the second is the key and the second one is the dictionary.

length = Dict::lookup 'a' {'a' = 1, 'b' = 2, 'c' = 3}

Building a dictionary from a sequence of tuples

Function from_seq builds a dictionary from a sequence of tuples.

Example:

Dict::from_seq [(1, 4), (2, 5), (3, 6)]

Will return {1 = 4, 2 = 5, 3 = 6}.

Turning a dictionary to a sequence of tuples

Function entries is the inverse operation of the from_seq function and it returns a sequence of tuples (key, value) for the provided dictionary.

Example:

Dict::entries {1 = 4, 2 = 5, 3 = 6}

Will return [(1, 4), (2, 5), (3, 6)].

Getting keys from the dictionary

Function keys returns a set of all keys for the provided dictionary.

Example:

Dict::keys {1 = 4, 2 = 5, 3 = 6}

Will return {1, 2, 3}.


Last update: August 16, 2020