Callables

A callable is an object that, given a set of inputs known as parameters produce one output known as the return value through a sequence of computations.

Declaration

A callable can be declared with the following syntax:

fun <identifier>(<param0>, <param1>, [...], <paramN>) = <expression>

where <identifier> is the name which the callable shall be refered to in the module, <param0> through <paramN> are the identifiers of each parameter, and <expression> is the expression that shall be evaluated when the callable is invoked.

Invokation

Callable invokation is done by specifying its identifier, then the list of its parameters enclosed in parenthesis:

<identifier>(<param0>, <param1>, [...], <paramN>)

Purity

A callable is called pure when it has no side-effects, and when given a set of parameters, two invokations does produce the same return value.

A common example of pure callables are the arithmetic operators.

Functions

Functions are the default (and most used) kind of callables. It has an internal context that is the parameters and local variables, and is destroyed when a return value is produced.

Coroutines

Coroutines are the second kind of callables, and can be inferred from the usage of the yield control flow keyword. They are much like functions, except that the internal context of the function is not discarded when a return value is produced. Instead, the context is saved, and the coroutine shall resume when it is invoked again later.

Tasks

Tasks are the final kind of callables, and they express a way to make asynchronous tasks units that can be passed on different execution environments. Tasks can be inferred from the usage of the offer control flow keyword, and much like functions, their execution context is destroyed after a return value has been offered.

Control Flow

In addition to the standard control flow statements, the following statements are provided to change the control flow in any callable:

• return <expr>: returns the value of the given expression in a function. Execution of the current function stops.
• yield <expr>: yields the value of the given expression in a coroutine. Execution resumes after this point when the coroutine is called again.
• offer <expr>: offers the value of the given expression in a task to the underlying task manager. Execution of the current function stops.