Representation of Modula programs

The preceding chapter has introduced a formalism, by which the structures of well-formed programs will subsequently be defined. It defines, however, merely the way in which programs are composed as sequences of symbols, in contrast to sequences of characters. This “shortcoming” is quite intentional: the representation of symbols (and thereby programs) in terms of characters is considered too much dependent on individual implementations for the general level of abstraction appropriate for a language definition. The creation of an intermediate level of representation by symbol sequences provides a useful decoupling between language and ultimate program representation. The latter depends on the available character set. As a consequence, we need to postulate a set of rules governing the representation of symbols as character sequences. The symbols of the Modula vocabulary are divided into the following classes: identifiers, numbers, strings, operators and delimiters, and comments.