ginger/docs/functions.md

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# Functions
Functions are first-class citizens in ginger. The simplest anonymous function
can be created like so:
```
(. fn [x]
(: + x 1))
```
This function takes in a single number and returns that number plus one. It
could be assigned to a variable on the package using `def`, or by using the
shortcut `defn`. The following two statements are equivalent:
```
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(. def incr
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(. fn [x]
(: + x 1)))
(. defn incr [x]
(: + x 1))
```
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## Function returns
### Single returns
A function returns whatever the last expression in its execution returned. For
example:
```
(. defn abs [x]
(. if (: >= x 0)
x
(: * -1 x)))
```
This function will return the argument `x` if it is greater than or equal to 0,
or `(* -1 x)` if it's not.
### Multiple returns
A function which wishes to return multiple arguments should return them as a
vector or list of arguments. The `let` function, which can be used to define
temporary variables in a scope, can deconstruct these multiple-returns:
```
# Returns two numbers which sum up to 10
(. defn sum-10 []
[4 6])
(. let [[foo bar] (: sum-10)
(: fmt.Println "%d + %d = 10" foo bar))
```
Functions defined within a go library which return multiple values can also be
deconstructed in a `let` statement:
```
(. let [[conn err] (: net.Dial "tcp" "localhost:80")]
# do stuff)
```
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## Variadic function
Functions may take in any number of variables using the `...` syntax, similar to
how go does variadic functions. The variadic variable must be the last in the
function's argument list, and is used as a list inside of the function. A list
may also be used as the input for a variadic function, also using the `...`
syntax.
The following is an example of both defining a variadic function and both ways
of using it. `+` is a variadic function in this example:
```
(. defn avg [...x]
(/
(+ x...)
(len x)))
(: fmt.Println (avg 1 2 3 4 5))
```
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## Tail-recursion
TODO