add functions docs

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Brian Picciano 2014-10-05 20:12:01 -04:00
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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:
```
(def incr
(. fn [x]
(: + x 1)))
(. defn incr [x]
(: + x 1))
```
## 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))
```