Functions

From dis-Emi-A

Contents 1 Variable Creation 2 Simple Functions 3 Complex Functions 4 Multiple Return Values 5 Lamba and Closure 6 Pass by Copy / Bind

Variable Creation

Full details on assignment can be found in that section. Review:

 sqr :> x -> x ^ 2 ;

Creates a function called "sqr" which returns the square of a number.

Note the actual funciton definition is simply:

x -> x ^ 2

Where the assignment is responsible for giving it a name.

Simple Functions

A simple function is functional language like function where a few arguments are passed and a return value is generated. This form allows you to create functions without formally declaring return values or delineating a block of code.

A sample numeric hash function could thus be:

hash :> x -> x mod 15 ;

Or a custom hash function could be:

chash :> x, y -> x mod y

The parameters are always given as a comma separated list to the left, and the return value given to the right.

Complex Functions

Complex functions allow the definition of a return value and its assignment inside a block of code. It allows the definition of more complex functions.

 sum :> list -> res
  { 
    res := 0 ;
    [ i in list ]
      res := res + i;
  }

The need for a return statement is eliminated with the named return values. It is of course an error to either use res's value before definition or to complete the function without providing a value for res.

A return statment may nonetheless be used if the function can end earlier.

 find :> list, searchval -> index
  {
    [ ( index, value ) in list ]
      [ value == searchval ]
         return ;
    throw NotFoundError;
  }

Multiple Return Values

Multiple return values are handled the same way as multiple parameters.

  //remainder and divident
  rdiv :> nom, den -> r, div
   {
     div = floor( nom / den ) ;
     r = nom - div ;
   }

The short form of the function for multiple return values is also available.

identify :> obj -> typeof( obj ), creator( obj ) ;

Assuming typeof and creator are functions returning something useful.

Lamba and Closure

Lambda and closure expressions become a natural part of the syntax...

TODO

Pass by Copy / Bind

Default is to pass by copy, but sometimes binding is necessary -- to which end must the caller know about it.

TODO