Closures are user defined methods which can be saved. They can be used as a prepared piece of code or to consume items from a thing, list, tuple or set. They can also be used by procedures.

Closure can be stored in a collection or assigned to a variable.

A closure starts with a |, then takes optional arguments and a | to close, followed by a statement. The most simple closure is ||nil which is a closure without arguments and returns the value nil when called.

More complex closures are also possible, check the last example below.


Function Description
call Call the closure with optional arguments.
def Return the definition of a closure using spaces, line-breaks and indentation.
doc Return the doc string of the closure.

Closures may be called recursively up to a recursion depth of 24. If this limit is exceeded, an error is raised. For example: a = ||a(); a();
…will raise operation_err() (maximum recursion depth exceeded)

Doc string

Doc strings can be set on closures. This is especially useful when closures are used inside a procedure since this gives the procedure a nice documentation string.

Usually, a doc string is just a normal string on top of a block in the closure.

For example:

|| {
    "this is a doc string.";

It is common to wrap a block scope within one or more functions. When this is the case, the doc string will be read from the first argument, only if the first non-function argument contains a block scope with a doc string.

For example, this closure contains a block scope wrapped with return and wse:

|| return(wse({
    "this is still a doc string, even while wrapped using `return` and `wse`.";
}), 2);


This code uses a simple closure together with map and call:

// create a simple closure which just adds one to a given value
add_one = |x| x+1;

// use the closure in a `map` function
map_result = [1, 2, 3].map(add_one);

// use the closure as a function call
call_result = add_one(41);

// return the result values
[map_result, call_result];

Return value in JSON format


Like explained, closures can accept multiple arguments and may contain a block scope instead of just a single line statement. Here is an example:

|name, age| {
    "Returns a thing with properties `name`, `age` and `time`.";

    assert(isstr(name) && name.len());
    assert(isint(age) && age >= 0);

    // this is the last statement so it will be the return value
        name: name,
        age: age,
        time: now()