Tacit programming: Difference between revisions

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</syntaxhighlight>

For a more complex example, the [[Haskell]] code {{<code|1=>p = ((.) f) . g}}</code> can be translated as:

<syntaxhighlight lang="python">

p = partial(compose, partial(compose, f), g)

</syntaxhighlight>

===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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In Unix scripting the functions are computer programs which receive data from [[Standard streams|standard input]] and send the results to [[Standard streams|standard output]]. For example,

<syntaxhighlight lang="bash">

sort | uniq -c | sort -rn

</syntaxhighlight>

is a tacit or point-free composition which returns the counts of its arguments and the arguments, in the order of decreasing counts. The {{Codemono|sort}} and {{Codemono|uniq}} are the functions, the {{Code|-c}} and {{Code|-rn}} control the functions, but the arguments are not mentioned. The pipe {{<Code>||}}</code> is the composition operator.

Due to the way pipelines work, it is normally possible only to pass one ''argument'' at a time in the form of a pair of standard [[input/output]] stream. Although extra [[file descriptor]]s can be opened from [[named pipe]]s, this no longer constitutes a point-free style.

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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.:

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In point-free style, this can be written in Python as:

<syntaxhighlight lang="python">

example = compose(foo, bar, baz)

</syntaxhighlight>

In jq, the equivalent point-free definition would be: