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: * 2-argument lambda (accumulator, (key, value)) returning a new value of an accumulator * initial value of the accumulator * dictionary to fold
This example shows how to sum up a dictionary:
Dict::fold (\acc (key, value) -> acc + value) 0 {'a' = 1, 'b' = 2, 'c' = 3}
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: * transducer * dictionary to reduce
Example with a map transducer:
Dict::reduce (Transducers::map \val -> val * 2 (0, \state val -> state + 1, identity)) {'a' = 1, 'b' = 2, 'c' = 3}
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}.