Tacit programming: Difference between revisions

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===Functional programming===

A simple example (in [[Haskell]]) is a program which computes the sum of a list of numbers. We can define the sum function recursively using a ''pointed'' style (cf. [[value-level programming|''value''-level programming]]) as:

<syntaxhighlight lang="haskell">sum [] = 0

sum (x:xs) = x + sum xs</syntaxhighlight>

sum [] = 0

</syntaxhighlight>

However, using a [[fold (higher-order function)|fold]], this can be replaced with:

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====jq====

[[jq (programming language)|jq]] is a [[JSON]]-oriented programming language in which the {{Code<code>||}}</code> symbol is used to connect filters to form a pipeline in a familiar way. For example:

[1,2] | add

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evaluates to 3. (Yes, the JSON array is a jq filter that evaluates to an array.)

Although similar to Unix pipelines, jq pipelines allow the incoming data to be sent to more than one recipient on the RHS of the '<code>|'</code> as though in parallel. For example, the program `<code>add/length`</code> will compute the average of the numbers in an array, so that:

[1,2] | add/length

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evaluates to [2,3,1.5]

A dot ('<code>.'</code>) can be used to define an attachment point on the RHS, e.g.:

1 | [., .]

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2 | pow(.; .)

evaluates to 4 since <code>pow(x;y)</code> is x to the power y.

=====Fibonacci sequence=====

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[0,1] | recurse( [last, add] ) | first

Here, <code>[0,1]</code> is the initial pair to be taken as the first two items

in the Fibonacci sequence. (The pair <code>[1,1]</code> could likewise be used for

the variant definition.)

The alphabetic tokens are built-in filters: `first` and `last`

emit the first and last elements of their input arrays respectively;

and `<code>recurse(f)`</code> applies a filter, f, to its input recursively.

jq also allows new filters to be defined in a tacit style, e.g.: