Miscellenaous Expressions

A few OQL operators cannot be easily classified in one of the previous categories. We choose to classify them in the miscellenaous operators. These operators are: bodyof, structof, [!] and import.

bodyof operator

The bodyof operaror is used to get the body of an OQL function. For instance, let the function fib: define fib(n) as (n < 2 ? n : fib(n-2) + fib(n-1)). The expression bodyof fib will return: "fib(n) ((n<2)?n:(fib((n-2))+fib((n-1))))". This operator could be applied to expression-functions (i.e. functions defined with the define/as operator) or statement-functions (i.e. functions defined with the function operator).

General Information
Operator	bodyof
Syntax	classof expr
Type	unary
Operand Type	ident denoting a function
Result Type	string
Function	returns the body of the function

Expression Examples
bodyof is_int	"is_int(x) ((typeof x)=="integer")"
bodyof first	"first(l) { if (((!is_list(l))&&(!is_array(l)))) return l; start:=0; f:=nil; for (x in l) if ((start==0)) { start:=1; f:=x; break; }; ; return f; }"
bodyof 1	raises an error

structof operator

The structof is used to get the meta-type of a struct atom. The meta-type of a struct atom is the list of the attributes of this struct. For instance, the meta-type of struct(a : 1, b : "hello") is the list composed of the two attribute a and b. The following expression structof struct(a : 1, b : "hello") returns list("a", "b").

General Information
Operator	structof
Syntax	structof expr
Type	unary
Operand Type	struct
Result Type	a list of strings
Function	returns the meta-type of the operand

Expression Examples
structof struct(alpha : 1, beta : 2)	list("alpha", "beta")
structof first(select struct(x: x.firstname) from Person x)	list("x")
structof 1	raises an error

[!] operator

The [!] is used to get the length (or size) of an ordered or unordered collection, a string or a struct. For instance, "hello"[!] returns 5, while list(1, 2, 3)[!] returns 3. Note that this operator is far more efficient than the strlen library function.

General Information
Operator	[!]
Syntax	expr [!]
Type	unary
Operand Type	string, collection or struct
Result Type	a int
Function	returns length of the operand

Expression Examples
(select Person)[!]	the number of person instances
(struct(a: 1, b:2, c: "hello"))[!]	3
("hello"+"world")[!]	10
"hello"+"world"[!]	raises an error

import operator

The import operator is used to import an OQL file in the current OQL session. Its operand is a string which denote the absolute path (i.e. beginning with a /) or relative path (i.e. not beginning with a /) of the file to import. When the path is relative, the OQL interpreter will look in every directories pointed by the EYEDB configuration variable oqlpath. By default, oqlpath is equal to %root%/etc/oql. If the file name has no .oql extension, the OQL interpreter will automatically adds one.

General Information
Operator	import
Syntax	import expr
Type	unary
Operand Type	string
Result Type	a string
Function	import the file

Expression Examples
import "stdlib"	"/usr/local/eyedb/etc/so/stdlib.oql"
import "roudoudou"	raises an error: cannot find file 'roudoudou'