COMS W4115 Programming Languages and Translators Event Driven State Language (EDSL) Language Reference Manual (LRM) Christopher D. Sargent [email protected] October 17, 20073. Language Manual This manual is intended to be chapter 3 of the final report and as such, the numbering convention starts at 3. It is assumed that the user has read and understands the proposal white paper and therefore this chapter needs no introduction. 3.1 Token A token can be whitespace, a comment, an identifier, a keyword, a literal, or an operator. 3.1.1 Whitespace Whitespace: „ „ „\t‟ „\n‟ „\r\n‟ Whitespace consists of blanks or spaces, horizontal tabs, and newlines, or a concatenation of one or several of these. For purposes of compatibility with UNIX and Windows platforms, a newline may be either a linefeed character or a carriage return followed by a linefeed. Whitespace serves no other purpose than to separate other tokens. 3.1.2 Comment Comment: Traditional-Comment End-of-Line-Comment Traditional-Comment: /* Comment-End Comment-End: * Comment-End-Star [^*] Comment-End Comment-End-Star: / * Comment-End-Star [^/*] Comment-End End-of-Line-Comment: // Characters-in-End-of-Line-CommentCharacters-in-End-of-Line-Comment: [^ „\n‟ „\r\n‟] Characters-in-End-of-Line-Comment [^ „\n‟ „\r\n‟] The traditional comment begins with the characters /* and ends with the characters */. It can span multiple lines, but it does not nest with other comments. The end-of-line comment begins with the characters//, and ends with the newline character or characters. 3.1.3 Identifier Identifier: Characters-in-Identifier Characters-in-Identifier: ([A-Z] | [a-z]) ([A-Z] | [a-z] | [0-9])* An identifier begins with at least one letter and follows with a sequence of zero or more letters and digits. Identifiers are case sensitive and may have any length, subject to platform specific limitations. 3.1.3.1 Keyword A keyword is an identifier that has special meaning within the language. Keywords should not be used except for their intended purpose. Keywords are identified within the following sections of this document by their courier font. 3.1.4 Literal Literal: Boolean-Literal Integer-Literal Real-Literal Boolean-Literal: true false Integer-Literal: Decimal-Literal Hexadecimal-LiteralBinary-Literal Decimal-Literal: [0-9]+ Hexadecimal-Literal: 0 (x|X) ([A-F] | [a-f] | [0-9])* Binary-Literal: 0 (y|Y) [0-1]* Real-Literal: „.‟ [0-9]+ Exponent? [0-9]+ („.‟ [0-9]+ Exponent? | Exponent) Exponent: (e|E) („+‟ | „-„)? [0-9]+ A Boolean literal has one of two values, either true or false. An integer literal can be a decimal, hexadecimal, or binary number. The prefix is necessary for an LL(2) parser to be able to distinguish the three different kinds of integer. A real literal “consists of an integer part, a decimal point, a fraction part, an e or E, an optionally signed integer exponent. … The integer and fraction parts both consist of a sequence of digits. Either the integer part or the fraction part (not both) may be missing; either the decimal point or the e and the exponent (not both) may be missing.”1 3.1.5 Operator The function of the operators may depend on their operands. See section 3.2 for their usage within expressions. 3.2 Type and Type Conversion There are four basic types. The first three types are simple value storage types. The last is unique in that it stores a value, but it also operates on that value. Like the Boolean literal, a Boolean variable takes either the true or false value. 1 Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language Second Edition (Murray Hill: Prentice-Hall, 1988) 194.The integer variable takes a 32-bit signed integer. The minimum value of an integer is -2147483648 and the maximum is 2147483647. The real variable takes a 64-bit double-precision real. Its size and representation are governed by ANSI/IEEE Std. 754-1985. A timer has the same size and representation as a positive real, but it is constantly decremented until its value reaches zero. Its units are seconds relative to wall-clock time. Automatic type conversion may occur as a result of certain operators and their required operands. Automatic or implicit conversion is the only allowed type conversion mechanism. 3.2.1 Boolean and Integer A bool may be converted to an int without loss. If its value is false, then its integer representation will be 0. If its value is true, then its integer representation will be 1. An int may be converted to a bool with data loss. If its value is 0, then its Boolean representation will be false. If its value is not 0 (either a positive or negative value), then its Boolean representation will be true. 3.2.2 Integer and Real An int may be converted to a real without loss. Its value is exactly the same, with the exception that it has a fractional component equal to zero. A real may be converted to an int with data loss. Not only will its fractional component be truncated towards zero, but if the magnitude of its whole number component exceeds the minimum or maximum for an integer, it will be reduced to that value. 3.2.3 Real and Timer A timer may not take a value that is not an acceptable real value. In addition, a timer may not store a negative value. If a timer is assigned a negative value, its sign will be inverted. The value that a timer currently has may be converted to a real without loss. 3.3 ExpressionThe precedence of the expressions is in order that the expressions are in, in this section. 3.3.1 Primary Expression primary-expression: Identifier Literal ( expression ) The primary expressions consist of identifiers, literals, and expressions in parentheses. Identifier See section 3.1.3. Literal See section 3.1.4. ( expression ) A parenthesized expression is equivalent to the same expression without the parentheses. 3.3.2 Unary Expression unary-expression: primary-expression -unary-expression !unary-expression The unary operators: - and ! evaluate from right-to-left. -unary-expression For the „-„ or „negative‟ operator, the result of the evaluation is the negative of the operand.
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