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Clojure - Simple projects - Encoding and decoding

Convert boolean true false to 1 and 0λ︎

A very simple example of encoding and decoding is converting the Clojure values of true and false to 1 and 0 respectively.

Using 1 for true and 0 for false has been a common idiom in programming languages, especially where a language did not include true and false syntax.

Define an association between valuesλ︎

Define a Clojure hash-map to associate the Clojure boolean true an false values to 1 and 0 respectively

{false 0
 true 1}

Find an associated value for the conversionλ︎

Using the get function the boolean-value is used to find a matching key in the map and if found the value that key is associated is returned.

(get {false 0 true 1} boolean-value)


(get {false 0 true 1} true)

A map can be called, just like a function. the boolean-value is passed to the map as a function argument. As with the get expression, if the map contains the key the associated value is returned.

({false 0 true 1} boolean-value)


({false 0 true 1} true)

Convert multiple boolean valuesλ︎

If there are a collection of boolean values to convert, the map function can be used to convert them all to 1 or 0.

Map this over a collection of values

(map {false 0 true 1} [collection-of-boolean-values])


(map {false 0 true 1} [true false false true true true false false true false true false false true])

How does this work?λ︎

The map function takes two arguments, a function and a collection. The map function calls the function given as an argument and calls it with each element of the collection in turn. The result of each call is remembered by the map function and when the last element of the collection has been used, a new collection of all the results is returned.

In the above example, the hash-map {false 0 true 1} acts as a function.

({false 0 true 1} true)

A hash-map acts as a function in that it can return an associated value when given a key as an argument.

Calling {false 0 true 1} with true as an argument returns the value 1.