Functions. #

In Cyber, there are first-class functions (or function values) as well as statically defined functions.

Static Functions. #

Static functions are not initally values themselves. They allow function calls to be optimal since they don’t need to resolve a dynamic value. A nice feature of Cyber’s static functions is they can be used just like a function value.

Static functions are declared with the func keyword and must have a name.

import m 'math'

func dist(x0, y0, x1, y1):
    dx = x0-x1
    dy = y0-y1
    return m.sqrt(dx^2 + dy^2)

Calling static functions is straightforward. You can also reassign or pass them around as values.

print dist(0, 0, 10, 20)

-- Assigning to a local variable.
bar = dist

-- Passing `dist` as an argument.
func squareDist(dist, size):
    return dist(0, 0, size, size)
print squareDist(dist, 30)

The function declaration can also be initialized to an expression that evaluates to a function. However, the expression can not contain any local variable references since it’s a static declaration. The function signatures also have to match.

func myAdd(a, b):
    return a + b
func add(a, b) = myAdd      -- Valid declaration.

myInc = func(a):
    return a + 1
func inc(a) = myInc         -- CompileError, referencing local variable `myInc`.

func foo(a, b, c) = myAdd   -- panic, signature mismatch.

Functions can return multiple values.

import {cos, sin} 'math'

func compute(rad):
    return cos(rad), sin(rad)
x, y = compute(pi)

Function Overloading. #

Static functions can be overloaded by the number of parameters in its signature.

func foo():
    return 2 + 2

func foo(n):
    return 10 + n

func foo(n, m):
    return n * m

print foo()         -- "4"
print foo(2)        -- "12"
print foo(20, 5)    -- "100"

Lambdas. #

Lambdas or function values can be assigned to variables or passed as arguments into other constructs.

When a lambda only returns an expression, it can be declared with a simplified syntax.

-- Passing simple lambda as an argument.
foo(word => toUpper(word))

-- A simple lambda with multiple arguments.
foo((word, prefix) => prefix + toUpper(word))

-- Assigning a simple lambda.
canvas.onUpdate = delta_ms => print delta_ms

Lambdas that need a block of statements can be declared with the func keyword without a name.

-- Assigning lambda block to a variable.
add = func (a, b):
    return a + b

-- Passing a lambda block as an argument.
canvas.onUpdate():
    ..func (delta_ms):
        print delta_ms

Passing a lambda block as a call argument is only possible in a call expression block. To understand how that works, see Function Calls.

Closures. #

In Cyber, lambdas can capture local variables in parent blocks. This example shows the lambda f capturing a from the main scope.

a = 1
f = func():
    return a + 2
print f()         -- "3"

In the following, a referenced in the lambda expression is captured from the scope of the static function add.

func add():
    a = 123
    return b => a + b
addTo = add()
print addTo(10)   -- "133"

However, static functions can not capture local variables.

a = 1
func foo():
    print a       -- Compile Error: Can't reference local from static function.

Function Calls. #

The straightforward way to call a function is to use parentheses.

d = dist(100, 100, 200, 200)

You can call functions with named parameters.

d = dist(x0: 10, x1: 20, y0: 30, y1: 40)

The shorthand method for calling functions omits parentheses and commas. This only works for functions that accept parameters:

d = dist 100 100 200 200  -- Calls the function `dist`.

func random():            -- Function with no parameters.
    return 4

r = random                -- Returns the function itself as a value. Does not call the function `random`.
r = random()              -- Calls the function `random`.

The top level arguments for the shorthand convention must be separated by whitespace. A string can contain whitespace since it’s surrounded by delimiters.

a = myFunc 'cyber script'

The following has a binary expression with spaces inbetween which is not allowed. Removing that whitespace fixes the call expression.

a = myFunc 1 + 2     -- Not allowed.
a = myFunc 1+2       -- Correct.

Wrapping arguments in parentheses allows you to keep the whitespace in the sub-expression.

-- This calls the function `myFunc` with 2 arguments.
a = myFunc 'hello' (1 + 2 * 3)

-- Nested function call using the shorthand convention.
a = myFunc 'hello' (otherFunc 1+2 'world')

The call expression block continues to add arguments from the block’s body. If arguments are omitted from the initial call expression they can be added inside using the .. syntax. Arguments mapped to named parameters have a key value syntax separated by a :. All other arguments are added into a list and passed as the last argument.

foo(123):
    ..func ():
        return 123
    param3: 123
    234
    bar()
    'hello'

In the example above, the function foo is called with 4 arguments. The first argument 123 is included in the starting call expression. The second argument is a function value inside the call expression block. The third argument is mapped to the param param3. Finally, the fourth argument is a list that contains 234, bar(), and 'hello'.