2.   LEXICAL STRUCTURE

2.1  CHARACTER SET AND TRANSLATOR INPUT

Programs are composed of any sequence of characters from the 95-character ASCII or basic 55-character set. Any program can be written using only the 55-character set given below. Rules for converting from the 95-character ASCII set to the 55-character set are given in the description for specific tokens and token separators.

RULES

No distinction is made between upper and lower case letters except within a string literal.

Basic 55-Character Set

95-Character ASCII Set

    All characters in the basic 55-character set plus

NOTES

    This document uses the 95-character ASCII set to describe the language.

2.2  TOKENS AND TOKEN SEPARATORS

C - identifier,   D - literal,   K - comment,   L - pragmat,  

A token is the basic component used to build all constructs of the language. It is an indivisible lexical unit that is interpreted as a complete 'word' by the translator. A token separator is required in some cases between tokens and can be used otherwise to improve readability. A token or token separator is composed of a contiguous sequence of characters.

RULES

Input text is organized into lines, each of which is composed of tokens and token separators. No token or token separator can extend over more than one line of text. An end of line, eol, is a token separator.

A token separator must appear between any two adjacent tokens, unless one of the tokens is a special symbol or an operator symbol
(such as < >) which does not have the form of an identifier (e.g., AND)). One or more token separators may appear between any two tokens.

EXAMPLES

2.3  TOKENS

2.3.1  RESERVED WORDS

Reserved words have a fixed meaning within the syntax of the language.

RULES

The following are reserved words:

NOTES

     Reserved words may not be redefined.

    No distinction is made in the user of upper or lower case characters in a reserved word, thus, end, End, END, and enD are all equivalent.

2.3.2  OPERATOR SYMBOLS

Operator symbols are names of functions which are invoked with a special prefix or infix syntax (see Section 5.2).

RULES

The operator symbols are:

NOTES

    The definition of operator symbol names is discussed in Section 13.2.

RED RATIONALE MODULO AND INTEGER DIVISION DIV was chosen over / for lexical consistency with MOD, and to make easy the user overloading of /. CATENATION A one character symbol (&) was preferred since it will be heavily used. LOGICAL AND SET OPERATORS Since there is no conventional symbol for symmetric difference, consistency and readability indicated the use of menumonic operators (AND, OR and NOT) rather than operator symbols (*, +, and -). RELATIONAL OPERATORS The relational operator symbols =, /, <, <=, >, and >= are required by SM 3-1C. Since = is used for equality, RED adopts the standard practice of using := for assignment, avoiding such error-prone constructs as X=Y=Z.

2.3.3  SPECIAL SYMBOLS

Special symbols are tokens which have special meaning in the syntax.

RULES

The table below lists the special symbols and their uses.

All of the special symbols, except [, ], and #, consist of characters exclusively from the 55-character set. The following 55-character alternates are provided.

2.3.4  IDENTIFIERS

An identifier is a name which is associated with a language construct by a definition (see Section 3.5).

RULES

Reserved words and operator symbols (e.g., AND) may not be used as identifiers.

All characters in an identifier, including underscore, are significant.

NOTES

     No distinction is mode in the use of upper or lower case charoctors in an identifier (e.g.,'Abc, abc, ond ABC are all equivalent).

EXAMPLES

2.3.5  LITERALS


E - int literal,   F - float literal,   G - emum literal,   H - string literal,   I - boolean literal,   J - indirect literal,  

Literals are used to specify values for some built-in types and for user-defined indirect types (see Section 4.4.3).

RULES

The values of all literals are known at translation time.

The rules for resolution of the type and subtype of a literal are described in Section 5.7.

NOTES

     The following sections describe specific literals. User-defined literals, which are language constructs rather then tokens, are described in Sections 5.7 and 13.5.

2.3.6  NUMERIC LITERALS

Numeric literals specify integer values for the INT type and floating point values for the FLOAT type.

RULES

A floating point literal in E form is interpreted as the decimal number times ten to the integer value following E. The default precision of a floating point number is the number of digits preceding E, minus any leading zeros to the left of the decimal point.

NOTES

     Numeric literals are always positive values. A negative literal is obtained by preceding the literal with the prefix minus operator. This operation is performed at translation time. `

    Because a float literal is a token, blanks may not appear within the float literal.

    The precision of a float literal is first determined by context and, if that is not sufficient, the default precision is used (see Section 5.7).

    No distinction is made in the use of upper or lower case e in a float literal.

EXAMPLES

2.3.7  ENUM LITERALS


C - identifer

An enum literal (enumeration literal) specifies a named value of an enumeration type.

NOTES

     The same enumeration literal may appear in several enumeration types. For example, the enumeration literal 'ORANGE may appear simultaneously in the ENUM types FRUIT and COLOR.

    Because an enum literal ia a token, no blank may appear between the apostrophe and the identifier.

    Because the enum literal is distinguished by an apostrophe, the identifier following the apostrophe may be defined in the same scope (i.e., RED may be the name of a variable in the same scope in which RED is an enum literal).

    The language views a character set as an enumeration type, where each character corresponds to an enum literal. `

    No distinction is made in use of upper or lower case (e.g., 'RED, 'Red, 'red, and 'reD are all equivalent).

EXAMPLES

2.3.8  STRING LITERALS

A string literal specifies a value of a STRING type. A string is a sequence of characters. Each character is an enumeration literal. If a string includes only those characters in the 95-character set, the special literal form, string literal, can be used. A string literal is considered to be a shorthand form for the concatenation of characters defined by enum literals>; e.g., "ABC" is considered a shorthand form of

RULES

'' (quote quote) is the 55-character set form of " (double quote).

NOTES

     A string literal may not extend over one line. If an end of line ia found before the terminating quote, the string literal token is terminated and an error message is issued. The & infix operator can be used to obtain a long string by concatenation.

    Upper or lower case characters are distinguished in strings; e.g., "ABC" ia not equivalent to "abc". All characters in the 95-character ASCII set have a corresponding enumeration literal (defined in Appendix C.15). For example, since 'lbracket is the enumeration literal for [ and 'number the enumeration literal for #, the string

    is equivalent to

EXAMPLES

2.3.9  BOOLEAN LITERALS

A boolean literal specifies a value of type BOOL.

2.3.10  INDIRECT LITERALS

The indirect literal NIL specifies that value of an indirect type (see Section 4.4.3) which points to no dynamic variable.

2.4  TOKEN SEPARATORS

2.4.1  COMMENT

A comment provides program documentation.

RULES

A comment is terminated by the end of the line on which it appears. Comments are ignored by the translator.

2.4.2  PRAGMAT

82 - pragmats

Pragmats supply information to the translator which does not affect language semantics. Pragmats are described in Appendix B.