Terminal Atom Syntax

To express the syntax of terminal atoms, we use the standard regular expression notation.

Integer Atom

Integers are coded on 64 bits.
The syntax for the integer type is one of the followings:

[0-9]+ 		 decimal base

0x[0-9a-fA-F]+ 		 hexadecimal

0[0-7]+ 		 octal

The domain for the integer type is as follows:

Minimal Value	Maximal Value
-9223372036854775808	9223372036854775807

A few examples:

13940     // integer expressed in the decimal base
0x273f1   // integer expressed in the hexadecimal base
0x273F1   // integer expressed in the hexadecimal base
0100      // integer expressed in the octal base

Float Atom

The syntax for floating point atoms is one of the following regular expressions:

[0-9]+\.[0-9]+?
[0-9]+?\.[0-9]+
[0-9]+\.[0-9]+?(e|E)[+-]?[0-9]+([fF]|[lL])?
[0-9]+?\.[0-9]+(e|E)[+-]?[0-9]+([fF]|[lL])?

The domain for the float type is as follows:

Minimal Value	Maximal Value
4.94065645841246544e-324	1.79769313486231570e+308

A few examples:

1.
1.23
.3
0.3039
1e+10
2.e+112
1.2e-100
.234e-200
.234e-200f
.234e-200F

String Atom

The syntax for the string type is as follows:
\"([^"]|\\\")*\"

The following escape sequences are interpreted:

Escape Sequence	Name	ASCII Name
\a	alert	BEL
\b	backspace	BS
\f	form feed	FF
\n	newline	NL (LF)
\r	carriage return	CR
\t	horizontal tab	HT
\v	vertical tab	VT
\\	backslash	\
\"	double quote	"
\'	single quote	'
\ooo	octal number	\ooo

A few examples:

"hello"
"hello \"world\""
"this is a multi-lines\ntext\n"
"this text contains escape sequences: \007\v\f\n''

Char Atom

The syntax for the char type is one of the followings:
'ascii character'
'\[0-7+]'
'\(x|X)[0-9a-fA-F+]'
'\a'
'\b'
'\f'
'\n'
'\r'
'\t'
'\v'

A few examples:

'a'
'b'
'\n'
'\a'
'\007'
'\x50'
'\x5F'

Boolean Atom

The syntax for a boolean atom is one of the followings:
true
false

Identifier Atom

The syntax for an identifier atom is as follows:
[a-zA-Z\$_#][a-zA-Z\$_0-9#]*

This means that an identifier must start whith a letter, a ``_'', a ``$'' or a ``#'' which may be followed by letters, digits, ``_'', ``$'' and ``#'' characters.

For instance, the following words are some valid identifiers:

a
alpha
beta1
alpha_beta
$a
oql$maxint
oql#2
$
#
_1

Note that identifiers beginning by oql$ or oql# are reserved for special used by the interpreter.

Oid Atom

The syntax for an oid is as following:
[0-9]+:[0-9]+:[0-9]+:oid

Note that oid atoms are not typed directly by the user, but are produced by the database via the OQL interpreter.
The following words are some syntaxically valid atom oids:

123.2.33373:oid
82727272.1.292828282:oid

Object Atom

The syntax for an atom object is as following:
[0-9a-fA-F]+:obj

Note that object atoms are not typed directly by the user, but are produced by OQL interpreter.
The following words are some syntaxically valid atom objects:

38383:obj
ea954:obj

Null Atom

The null atom denotes an unitialized value. Its type depends on the context. It can denote a unitialized integer, float, char, string or oid.

The syntax for a null atom is one of the followings:
null
NULL

Nil Atom

The nil atom denotes the empty atom.
The syntax for a nil atom is as follows:
nil