Flow Control

Flow control statements determine the sequence of operations in a program by conditionally executing parts of the program, looping over parts of the program, calling other pages code, and determining what to do in case of errors.

Conditional statements are represented by if-then-else constructs, with optional elif clauses.

Loops can be implemented using while statemnts, repeat statements, or for statements.

There are two ways to execute the code associated with another web page. Both allow extending the functionality of a web page by re-using the code of other pages (and formatting, using the first method):

• The call function takes as a paramter a web page file name, simulates a request to that page, and returns the formatted response that should be assigned to a variable of type page. Later, the content can be merged with other strings or pages in a larger response. 
  
• The import statement is a way to incorporate the compiled code of the .icod file of another web page in the current page, as an opaque block of declarations and statements. The global variables in the included code are going to be visible in the current block of statements. To avoid name conflicts, an optional prefix can be applied to all the imported variable names.

The request processing language does not contain a way to declare functions, but offers parameterized macro processing capabilities, which can be used to create the equivalent of ?inlined functions and make possible other more flexible solutions.

A robust error handling mechanism is based on raise and onerror statements, which can also handle errors returned from imported code.