xHarbour

xHarbour has 6 scalar types: Nil, String, Date, Logical, Number, Pointer, and 4 complex types: Array, Object, CodeBlock, and Hash. A scalar holds a single value, such as a string, number, or reference to any other type. Arrays are ordered lists of scalars or complex types, indexed by number, starting at 1. Hashes, or associative arrays, are unordered collections of any type values indexed by their associated key, which may be of any scalar or complex type.

Literal (static) representation of scalar types:

• Nil: NIL
• String: "hello", 'hello', [hello], or E"hello\n"
• Date: ctod("2005-03-17" )
• Logical: .T., .F.
• Number: 1, 1.1, -1, 0xFF

Complex Types may also be represent as literal values:

• Array: { "String", 1, { "Nested Array" }, .T., FunctionCall(), @FunctionPointer() }
• CodeBlock: { |Arg1, ArgN| Arg1 := ArgN + OuterVar + FunctionCall() }
• Hash: { "Name" => "John", 1 => "Numeric key", "Name2" => { "Nested" => "Hash" } }

Hashes may use any type including other Hashes as the Key for any element. Hashes and Arrays may contain any type as the Value of any member, including nesting arrays, and Hashes.

Codeblocks may have references to Variables of the Procedure/Function>method in which it was defined. Such Codeblocks may be returned as a value, or by means of an argument passed BY REFERENCE, in such case the Codeblock will "outlive" the routine in which it was defined, and any variables it references, will be a DETACHED variable.

Detached variables will maintain their value for as long as a Codeblock referencing them still exists. Such values will be shared with any other Codeblock which may have access to those same variables. If the Codeblock did not outlive its containing routine, and will be evaluated within the lifetime of the routine in which it is defined, changes to its Detached Variables(s) by means of its evaluation, will be reflected back at its parent routine.

Codeblocks can be evaluated any number of times, by means of the Eval( BlockExp ) function.

All types can be assigned to named variables. Named variable identifiers are 1 to 63 characters long, start with [A-Z|_] and further consist of the characters [A-Z|0-9|_] up to a maximum of 63 characters. Named variables are not case sensitive.

Variables have one of the following scopes:

• LOCAL: Visible only within the routine which declared it. Value is lost upon exit of the routine.
• STATIC: Visible only within the routine which declared it. Value is preserved for subsequent invocations of the routine. If a STATIC variable is declared before any Procedure/Function/Method is defined, it has a MODULE scope, and is visible within any routine defined within that same source file, it will maintain its life for the duration of the application lifetime.
• GLOBAL Visible within any routine defined in the same source module where the GLOBAL variable is declared, as well as any routine of any other source module, which explicitly declares it, by means of the GLOBAL EXTERNAL declaration. Both GLOBAL and GLOBAL EXTERNAL declarations must be declared before any Procedure/Function/Method is defined.
• PRIVATE: Visible within the routine which declared it, and all routines called by that routine.
• PUBLIC: Visible by all routines in the same application.

LOCAL, STATIC, and GLOBAL are resolved at compile time, and thus are much faster than PRIVATE and PUBLIC variables which are dynamic entities accessed by means of a runtime Symbol table. For this same reason, LOCAL, STATIC and GLOBAL variables are not exposed to the Macro compiler, and any macro code which attempts to reference them will generate a runtime error.

Due to the dynamic nature of PRIVATE and PUBLIC variables, they can be created and destroyed at runtime, can be accessed and modified by means of runtime macros, and can be accessed and modified by Codeblocks created on the fly.

The basic control structures include all of the standard dBase, and Clipper control structures as well as additional ones inspired by the C or Java programming languages:

[DO] WHILE ConditionExp
   ...
   [LOOP]
   [EXIT]
END[DO]

FOR Var := InitExp TO EndExp [STEP StepExp]
   ...
   [LOOP]
   [EXIT]
NEXT

FOR EACH Var IN CollectionExp
   ...
   [HB_EnumIndex()]
   [LOOP]
   [EXIT]
NEXT

IF CondExp
   ...
[ELSEIF] CondExp
   ...
[ELSE]
   ...
END[IF]

DO CASE
   CASE CondExp
      ...
   [CASE CondExp]
      ...
   [OTHERWISE]
      ...
END[CASE ]

IF CondExp
   ...
ELSEIF CondExp
   ...
[ELSEIF CondExp]
   ...
[ELSE]
   ...
END[IF]

SWITCH SwitchExp
   CASE LiteralExp
      ...
      [EXIT]

   [CASE LiteralExp]
      ...
      [EXIT]

   [DEFAULT]
      ...
END

BEGIN SEQUENCE
   ...
   [BREAK]
   [Break([Exp])]
RECOVER [USING Var]
   ...
END[SEQUENCE]

BEGIN SEQUENCE
   ...
   [BREAK]
   [Break()]
END[SEQUENCE]

TRY
   ...
   [BREAK]
   [Break([Exp])]
   [Throw([Exp])]
CATCH [Var]
   ...
END

TRY
   ...
   [BREAK]
   [Break([Exp])]
   [Throw([Exp])]
CATCH [Var]
   ...
FINALLY
   ...
END

TRY
   ...
   [BREAK]
   [Break([Exp])]
   [Throw([Exp])]
FINALLY
   ...
END

[STATIC] PROCEDURE SomeProcedureName
[STATIC] PROCEDURE SomeProcedureName()
[STATIC] PROCEDURE SomeProcedureName( Param1' [, ParamsN] )

INIT PROCEDURE SomeProcedureName
EXIT PROCEDURE SomeProcedureName

[STATIC] FUNCTION SomeProcedureName
[STATIC] FUNCTION SomeProcedureName()
[STATIC] FUNCTION SomeProcedureName( Param1' [, ParamsN] )

Procedures/functions in xHarbour can be specified with the keywords PROCEDURE, or FUNCTION. Naming rules are same as those for Variables (up to 63 characters non case sensitive). Both Procedures and Functions may be qualified by the scope qualifier STATIC to restrict their usage to the scope of the module where defined.

The INIT or EXIT optional qualifiers, will flag the procedure to be automatically invoked just before calling the application startup procedure, or just after quitting the application, respectively. Parameters passed to a procedure/function appear in the subroutine as local variables, and may accept any type, including references.

Changes to argument variables are not reflected in respective variables passed by the calling procedure/function/method unless explicitly passed BY REFERENCE using the @ prefix.

PROCEDURE have no return value, and if used in an Expression context will produce a NIL value.

FUNCTION may return any type by means of the RETURN statement, anywhere in the body of its definition.

An example procedure definition and a function call follows:

x := Cube( 2 )

FUNCTION Cube( n )
RETURN n ** 3

xHarbour extends the Clipper Replaceable Database Drivers (RDD) approach. It offers multiple RDDs such as DBF, DBFNTX, DBFCDX, DBFDBT, and DBFFPT. In xHarbour multiple RDDs can be used in a single application, and new logical RDDs can be defined from combination of other RDD. The RDD architecture allows for inheritance, so that a given RDD may extend the functionality of other existing RDD(s). 3rd party RDDs, like RDDSQL, RDDSIX, RMDBFCDX, Advantage Database Server, and Mediator exemplify some of the RDD architecture features.

xHarbour also offers ODBC support by means of an OOP syntax, and ADO support by means of OLE.

One of the most powerful features of the xBase languages is the MACRO Operator '&'. xHarbour’s implementation of the Macro Operator allows for runtime compilation of any valid xHarbour expression. Such compiled expression may be used as a VALUE, i.e. the right side of an Assignment, but such compiled expression may be used to resolve the LEFT side of an assignment, i.e. PRIVATE, or PUBLIC variables, or Database FIELD.

Additionally the Macro Operator may compile and execute function calls, complete assignments, or even list of arguments, and the result of the macro may be used to resolve any of the above contexts in the compiled application. IOW, any xHarbour application may be extended, and/or modified in runtime, to compile and execute additional code on demand.

The xHarbour implementation of this feature is so complete that the xHarbour interpreter, xbScript, uses it heavily, to compile xHarbour scripts.

Syntax:

 &( ... )

The text value of the expression '...' will be compiled, and the value resulting from the execution of the compiled code is the result.

 &SomeId

is the short form for &( SomeId ).

 &SomeId.postfix

is the short form of &( SomeId + "postfix" ).

xHarbour is also available as an interpreted language in few flavors of scripting engines.

• Stand alone Interpreter: Portable, self-contained, interpreter xBaseScript.
• ActiveScript: Microsoft ActiveScript compliant OLE DLL, which supports xHarbour scripting in:
  • Windows Script Host (WSH).
  • Internet Explorer, HTML client side scripting.
  • IIS, and any other ASP compliant server.

• Official site
• Object Oriented Harbour GUI (ooHG)
• FiveWin
• Xailer
• xHarbour.com