The Fortress Language Specification - CiteSeerX

escape sequences are useful for ASCII “shorthands” that begin with a lowercase letter or are not restricted words,
and when the escape sequence is immediately followed in the string by a letter, digit, or underscore. For example,
"\beta" evaluates to a string containing a backspace character (indicated by \b) followed by the letters e, t, and a,
but "\’beta’" evaluates to a string containing the single letter β. 5 As another example, "x\AND\’NOT’y" becomes
"x∧¬y", but "x\AND\NOTy" is a static error, because the name “NOTy” does not correspond to a Unicode character.
Also, the string "Foo\’[\’T\’\]’" becomes "FooT".
It is a static error if an unescaped backslash is immediately followed by a character other than another backslash, an
apostrophe, a string literal delimiter, or a restricted-word character. In addition, it is also a static error if an unescaped
backslash within a string literal is followed by any lowercase letter other than ‘b’, ‘t’, ‘n’, ‘f’ or ‘r’. This rule
preserves a certain level of compatibility with the C and Java programming languages.
Unlike elsewhere in a program, the enclosed characters of a string literal are not generally subject to the second
phase of ASCII conversion (word pasting across line terminators still occurs within string literals). However, ASCII
conversion may affect (and often replace) restricted-word and quoted-character escape sequences. Specifically, the
restricted word of a restricted-word escape sequence and the sequence of characters between the apostrophes of a
quoted-character escape sequence are subject to ASCII conversion. If that sequence of characters would be replaced
by a single Unicode character, then the entire escape sequence is replaced by that character, unless the replacement
character is a string literal delimiter, in which case the escape sequence is replaced by a backslash followed by the
replacement character. For example, the string literal "GAMMA" is unchanged by ASCII conversion, but "\GAMMA" and
"\’GAMMA’" are both changed to "Γ". The string literal "\\GAMMA" is also unchanged by ASCII conversion, because
the sequence \\ is an escaped backslash; this string literal evaluates to a string value consisting of the six characters:
\, G, A, M, M, and A. See Appendix E for a detailed discussion of the ASCII conversion process.
The formatting of identifiers and numerals described in Section 5.17 is not performed within string literals.
5.11 Boolean Literals
The boolean literals are false and true .
5.12 The Void Literal
The void literal is () (pronounced “void”).
5.13 Numerals
Numeric literals in Fortress are referred to as numerals. Numerals may be either simple or compound.
A numeral may consist of several words separated by spaces or a ‘ . ’ character. We adopt the following terminology:
• A simple numeral fragment is a word that begins with a digit. and consists of only letters and digits.
• A compound numeral fragment is a simple numeral fragment immediately followed by a ‘ . ’ character immediately
followed by a word that consists of only letters and digits.
• A sequence of characters is a numeral prefix if it is either a numeral fragment (simple or compound) or a numeral
prefix immediately followed by a space immediately followed by a numeral fragment (simple or compound).
5 Actually, the escape sequence \’beta’ is replaced by β during ASCII conversion.
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