Loglan 82, A micro-manual of the programming language - Basic constructs and facilities

3) Modularity

Modular structure of the language is gained due to the large set of means for module nesting and extending. Program modules (units) are blocks, procedures, functions, classes, coroutines and processes. Block is the simplest kind of unit. Its syntax is the following:

The sequence of statements commences with the keyword begin (it may be omitted when this sequence is empty). The lists of declarations define the syntactic entities (variables, constants, other units), whose scope is that block. The syntactic entities are identified in the sequence of statements by means of names (identifiers).

Example:

In the lists of declarations semicolons terminate the whole lists, not the lists elements. Any declaration list must begin with the pertinent keyword (var for variables, const for constants etc.). The value of an expression defining a constant must be determinable statically (at compilation time).

Program in LOGLAN-82 may be a block or alternatively may be of the following form:

Then the whole program can be identified by that name (the source as well as the object code).

A block can appear in the sequence of statements (of any unit), thus it is a statement. (Main block is assumed to appear as a statement of the given job control language.)

For the execution of a block statement the object of block is created in a computer memory, and then, the sequence of statements is performed. The syntactic entities declared in the block are allocated in its object. After a block's termination its object is automatically deallocated (and the corresponding space may be immediately reused).

The modular structure of the language works "in full steam" when not only blocks, but the other kinds of units are also used. They will be described closer in the following points.

Unit nesting allows to build up hierarchies of units and supports security of programming. It follows from the general visibility rules; namely, a syntactic entity declared in an outer unit is visible in an inner one (unless hidden by an inner declaration). On the other hand, a syntactic entity declared in an inner unit is not visible from an outer one.

Example:

In this program, first the main block statement is executed (with variables a,b,c,i,j,k). Next, after the read statement, the inner block statement is executed (with variables j,k). In the inner block the global variables j,k are hidden by the local ones.