10. Methods

A method is a scoped group of instructions as a value, that may be executed given any number of arguments as input and that may output any number of values. A method may be overloaded with different kinds of inputs or outputs.

The input of a method comes in the form of a collection of variables called arguments. Input to a method must match exactly one overload.

A method must be defined with a name (see. Lambdas for anonymous methods) and can be overloaded with multiple definitions.

At any point in the method a return statement may be made to cause the method to complete and take the given value as the output of the method call. When the return value of a method is explicitly defined, all possible execution paths must end with a return statement.

Methods are also valid values, and can thus be assigned to Variables. A variable that is of a method type may be assigned any methods with compatible overloads.

See also

Lambdas
Another kind of method

10.1. Type Inference

Method arguments may be defined without a type. In this case, the type is determined by every action involving that argument. From this it builds a “type expectation” that is used at compile time to check whether arguments are valid.

For instance, if a method is defined as:

def intAdd(x, y) -> Int
  return x + y
end

Then the type expectation of x is that it has a method + that can take one argument y and returns a type compatible with Int.

The compiler may create multiple actual functions for each kind of call, for these sorts of methods.

10.2. Syntax

Argument             ::=  Variable [ "=" Value ]
MethodPrototype      ::=  Identifier "(" [ Argument [ "," Argument ]* ] ")" [ "->" Value ]
Return               ::=  "return" [Value]
MethodInstruction    ::=  Instruction | Return
MethodInstructionSet ::=  ( MethodInstruction \n )*
Method               ::=  "def" MethodPrototype MethodInstructionSet "end"

10.3. Examples

def double(x:Float) -> Float
  return x * 2
end

def double(x) -> Int
  return x * 2
end

def double()
  return 2
end

double(2) #=> 4
double() #=> 2

def add(a:Int, b:Int) -> Int
  return a + b
end

def add(a:Float, b:Float) -> Float
  return a + b
end

reduce(add, [1, 2, 3, 4]) #=> 10
reduce(add, [3.0, 8.2, 7.3]) #=> 18.5