Iteration

Iteration is supported through a number of statements, as well as through recursive functions.

Iteration Statements

The statements supporting iteration are described in detail in Chapter 14, The Built-In Macros and Special Definitions.

**Table 4-3** Iteration Statements
Macro	Description	Page
`while`	Repeatedly executes a body until a test expression is false.	399
`until`	Repeatedly executes a body until a test expression is true.	400
`for`	Performs general iteration over a body, updating bindings and performing end tests on each iteration.	400

Tail Recursion

Implementations are encouraged to optimize tail recursive function calls whenever possible. Tail recursion occurs when a function F₁ returns the values of a call to another function F₂. In many cases, this can be used to create loops using self-recursive or mutually recursive functions. (Among the cases that cannot be optimized are those in which the return value types of F₁ and F₂ differ, requiring the F₁ to check the types of the values before returning them.)

The following example uses tail recursion to compute the name of the root volume on which a given file system object is stored.

define method root-volume-name (f :: <file-or-directory>)
  if ( root-volume?(f) ) 
    f.name
  else 
    root-volume-name(f.container)
  end if;
end method;

The example above can execute with constant stack size, regardless of how deeply nested the file system hierarchy may be.