The Fortress Language Specification - CiteSeerX

Chapter 13
Expressions
Fortress is an expression-oriented language. Syntactically, the positions in which an expression may legally appear
(value context) is determined by the nonterminal Expr in the Fortress grammar, defined in Appendix G.
13.1 Literals
Syntax:
Value ::= Literal
Fortress provides boolean literals, () literal, character literals, string literals, and numeric literals. Literals are values;
they do not require evaluation.
The literal false has type BooleanLiteralfalse . The literal true has type BooleanLiteraltrue .
The literal () is the only value with type (). Whether any given occurrence of () refers to the value () or to the type
() is determined by context.
A character literal has type Character. Each character literal consists of an abstract character in Unicode 5.0 [25],
enclosed in single quotation marks (for example, ‘a’, ‘A’, ‘$’, ‘α’, ‘⊕’). For convenience, the single quotes may be
either true typographical “curly” single quotation marks or a pair of ordinary apostrophe characters (for example, ’a’,
’A’, ’$’, ’α’, ’⊕’). See Section 5.9 for a description of how names of characters may be used rather than actual
characters within character literals, for example ‘APOSTROPHE’ and ‘GREEK CAPITAL LETTER GAMMA’.
A string literal has type String. Each string literal is a sequence of Unicode 5.0 characters enclosed in double quotation
marks (for example, “Hello, world!” or “π r 2 ”). For convenience, the double quotes may be either true typographical
“curly” double quotation marks or a pair of “neutral” double-quote characters (for example, "Hello, world!"
or "π r 2 "). Section 5.10 also describes how names of characters may be used rather than actual characters within
string literals. One may also use the escape sequences \b and \t and \n and \f and \r as described in [5].
Numeric literals in Fortress are referred to as numerals, corresponding to various expressible numbers. Numerals may
be either simple or compound (as described in Section 5.13).
A numeral containing only digits (let n be the number of digits) has type NaturalNumeraln, 10, v where v is the
value of the numeral interpreted in radix ten. If the numeral has no leading zeros, or is the literal 0 , then it also has
type Literalv .
A numeral containing only digits (let n be the number of digits) then an underscore, then a radix indicator (let r be the
radix) has type NaturalNumeralWithExplicitRadixn, r, v where v is the value of the n-digit numeral interpreted
in radix r.
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