Lexical Elements.

For the purpose of this section, the POSIX Extended Regular Expressions (ERE) syntax is used to describe the production of lexical elements. The POSIX regular expression is chosen for it being vendor neutral. There's a difference between the POSIX semantic of regular expression and PCRE semantic, the latter of which is widely used in many programming languages even on POSIX platforms, most notably Perl, Python, PHP, and have been adopted by JavaScript. Care have been taken to ensure the expressions used in this chapter are interpreted identically under both semantics.

Comments

Comments in the language begin with 2 forward slashses: //, and span towards the end of the line. Another form of comments exists, where it begins with /* and ends with */ - this form of comment can span multiple lines.

Comments in the following explanatory code blocks use the same notation as in the actual language.

Identifiers and Keywords

An identfier has the following production: [_[:alpha:]][_[:alnum:]]*. A keyword is an identifier that matches one of the following:

// Types:
long ulong double val ref

// Special Values:
true false null

// Phrases:
return break continue and or _Fallback

// Statements and Declarations:
decl

// Control Flows:
if else elif while do for

// Functions:
subr method ffi this

// Translation Unit Interface:
_Include extern

Numbers

Decimal integer literals have the following production: [1-9][0-9]*[uU]?. When the literal has the "U" suffix, the literal has type ulong, otherwise, the literal has type long.

Octal integer literals have the following production: 0[0-7]*. An octal literal always has type ulong.

Hexadecimal integer literals have the following production: 0[xX][0-9a-fA-F]+. A hexadecimal literal always has type ulong.

Fraction literals has the following production: [0-9]+\.[0-9]*|\.[0-9]+. The literal always has type double.

Decimal scientific literals is a fraction literal further suffixed by a decimal exponent literal production: [eE][-+]?[0-9]+. The digits of the production indicates a power of 10 to raise fraction part to.

Hexadecimal fraction literal has the following production: 0[xX]([0-9a-fA-F]+.[0-9a-fA-F]*|.[0-9a-fA-F]+) - this production is NOT a valid lexical element in the language, but hexadecimal scientific literal is, which is defined as hex fraction literal followed by hexadecimal exponent literal - having the production: [pP][-+]?[0-9]+. The digits of the production indicates a power of 2 to raise the fraction part to.

Characters and Strings

Character and string literals have the following production: ['"]([^\]|\\(["'abfnrtv]|x[0-9a-fA-F]{2,2}|[0-7]{1,3}))['"]

In the 2nd subexpression, each alternative have the following meanings:

1. Escaping
   • For single and double quote characters, they're represented literally and don't delimit the literal.
   • 'a' indicates the BEL ASCII 'bell' control character,
   • 'b' indicates the BS ASCII backspace character,
   • 'f' indicates the FF ASCII form-feed character,
   • 'n' indicates the LF ASCII line-feed character,
   • 'r' indicates the CR ASCII carriage return character,
   • 't' indicates the HT ASCII horizontal tab character,
   • 'v' indicates the VT ASCII vertical tab character.
2. Hexadecimal byte literal. The first character is interpreted as the high nibble of the byte, while the second the low.
3. Octal byte literal. The characters (total 3 at most) are interpreted as an octal integer literal used as value for the byte. If there are 3 digits, then the first digit must be between 0 and 3.

When single-quoted, the literal is a character literal having the value of the first character as type long, the behavior is implementation-defined if there are multiple characters.

When double-quoted, the literal is a string literal having type str.

Punctuations

A punctuation is one of the following:

( ) [ ] =? . ++ -- + - ~ ! * / %
<< >> >>> < > & ^ |
<= >= == != === !== && || ?? ? :
= *= /= %= += -= <<= >>= >>>= &= ^= |= &&= ||= ,
; { }