`fastn` supports functions which users can create to execute their own logic in their `fastn` documents. It also provides various [`built-in-functions`](/built-in-functions/) which users can use anywhere in their `fastn` document.

How to create functions ?

To create a function, you need to follow the function declaration syntax which is as follows:

Function Declaration syntax

--  (, , ...):
 : 
 : 
...

Lang:

ftd

Using the above declaration syntax, a simple `add()` function is defined below which takes two integer as arguments and returns the added value.

Sample `add()` function

-- integer add(a, b):
integer a:
integer b:

a + b

Lang:

ftd

How to use your functions ?

Once functions have been defined, you can use these functions by invoking it by using `$`.

Sample code using add() function

Input

-- integer add(a, b):
integer a:
integer b:

a + b

-- ftd.column:
spacing.fixed.px: 10
color: $inherited.colors.text

-- ftd.text: Adding 35 and 83

-- ftd.integer: $add(a=35, b=83)

-- end: ftd.column

Lang:

ftd

Output

Adding 35 and 83

118

Some frequently used functions

Below mentioned are some of the most frequently used functions which can be created as per the requirement and are not part of `fastn`.

Clamp

Clamp functions are used to limit your given value between certain range.

Regular Clamp

This function will clamp the value between 0 and `max`. Value will range from `[0,max]` given `max > 0`.

Sample code using `regular-clamp()`

Input

-- integer $num: 0

-- display-integer: $num
$on-click$: $regular-clamp($a = $num, by = 1, max = 6)

-- void regular-clamp(a,by,max):
integer $a:
integer by:
integer max:

a = (a + by) % (max + 1)

Lang:

ftd

Output

Clamp with min and max

This function will clamp the value between `min` and `max`. Value will range from `[min,max]` given `max > min`.

Sample code using `clamp_with_limits()`

Input

-- integer $n: 1

-- display-integer: $n
$on-click$: $clamp_with_limits($a = $n, by = 1, min = 1, max = 6)

-- void clamp_with_limits(a,by,min,max):
integer $a:
integer by: 1
integer min: 0
integer max: 5

a = (((a - min) + by) % (max + 1 - min)) + min

Lang:

ftd

Output

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[💻️](/community/)

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Quick links:

- [Install `fastn`](install/) - [Create `fastn` package](create-fastn-package/) - [Expander Crash Course](expander/) - [Syntax Highlighting in Sublime Text](/sublime/)

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