Contents Next

3.1   Lexical conventions

Blanks

The following characters are considered as blanks: space, newline, horizontal tabulation, carriage return, line feed and form feed. Blanks are ignored, but they separate adjacent identifiers, literals and keywords that would otherwise be confused as one single identifier, literal or keyword.

Comments

Comments are introduced by the two characters (*, with no intervening blanks, and terminated by the characters *), with no intervening blanks. Comments are treated as blank characters. Comments do not occur inside string or character literals. Nested comments are handled correctly.

Identifiers

ident ::= letter   { letter | 0...9| _| '}
letter ::= A ... Z | a ... z

Identifiers are sequences of letters, digits, _ (the underscore character), and ' (the single quote), starting with a letter. Letters contain at least the 52 lowercase and uppercase letters from the ASCII set. The current implementation also recognizes as letters all accented characters from the ISO 8859-1 (``ISO Latin 1'') set. All characters in an identifier are meaningful. The current implementation places no limits on the number of characters of an identifier.

Integer literals

integer-literal ::= [ -] { 0...9 }+
  | [ -] ( 0x| 0X) { 0...9| A...F| a...f }+
  | [ -] ( 0o| 0O) { 0...7 }+
  | [ -] ( 0b| 0B) { 0...1 }+

An integer literal is a sequence of one or more digits, optionally preceded by a minus sign. By default, integer literals are in decimal (radix 10). The following prefixes select a different radix:
Prefix Radix
0x, 0X hexadecimal (radix 16)
0o, 0O octal (radix 8)
0b, 0B binary (radix 2)
(The initial 0 is the digit zero; the O for octal is the letter O.) The interpretation of integer literals that fall outside the range of representable integer values is undefined.

String literals

string-literal ::= " { string-character } "
string-character ::= regular-char
  | \ ( \ | " | n | t | b | r)
  | \ ( 0...9) ( 0...9) ( 0...9)

String literals are delimited by " (double quote) characters. The two double quotes enclose a sequence of either characters different from " and \, or escape sequences from the table below:
Sequence Character denoted
\\ backslash (\)
\" double quote (")
\n newline (LF)
\r return (CR)
\t horizontal tabulation (TAB)
\b backspace (BS)
\ddd the character with ASCII code ddd in decimal

The current implementation places no restrictions on the length of string literals.

Infix symbols

infix-symbol ::= < { operator-char } | > { operator-char } | < > | no-inf-no-sup   { operator-char }
operator-char ::= < | > | no-inf-no-sup
no-inf-no-sup ::= ! | # | $ | % | & | * | + | - | . | / | = | ? | @ | ^ | | | ~

Sequences of ``operator characters'', such as <=> or !!, are read as a single token from the infix-symbol class. These symbols are parsed as infix operators inside expressions, but otherwise behave much as identifiers.

Warning: due to the concrete syntax of types that includes much < and > in sequence, the only identifiers that contain only < and > are <, > and <>.

Keywords

The identifiers below are reserved as keywords, and cannot be employed otherwise: 
    and       do            else          end           external
    false     if            in            init          let
    loc       open          primitive     reply         spawn
    then      to            true          type          val
    where     with
The following character sequences are also keywords: 
    ->    .     |

Ambiguities

Lexical ambiguities are resolved according to the ``longest match'' rule: when a character sequence can be decomposed into two tokens in several different ways, the decomposition retained is the one with the longest first token.

Contents Next