4GL Programming language.docx

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4GL Programming language

4GL programming language was born in Informix corp., about 15 years ago.Because of that, and not to conflict with with 4GL as general programming

concept (BASIC is in principle also Fourth Generation Language, as opposed to

C, that is Third Generation Language), we should refer to basic 4GL syntax asI-4GL.

Today, even among Informix-distributed products, there is distinction

among "classic" I-4GL and D4GL (Informix name for 4Js 4gl compiler), that

introduced number of language enhancements. Then Informix implemented

some of this enhancements back to "classic" 4gl, and added some of it's own (v7.3), that 4Js in turn implemented in 'Universal Compiler" V3 (this is actual

name for 4Js product that Informix distributes under the name "D4GL" -Dynamic 4GL.)

Confused? Why am I not surprised. So here is how we will refer to differentimplementations of LANGUAGE syntax:

I4GL - Informix non-GUI, a.k.a. "classic" products syntax, V 7.3 D4GL - 4Js extended syntax, including I4GL A4GL - Aubit 4GL specific syntax, including I4GL. x4GL - all of the above as general name for allLucky for us, Querix decided that it will not change language, and instead do

all GUI related configuration from separate configuration files.

Aubit 4GL, as package, and A4GL, as language definition, is a superset of

I4GL. Our first aim is to provide full UNCONDITIONAL compatibility withI4GL.

Since this means that 90% of the syntax used in A4GL will be I4GL, and sincethis document is not intended to be I4GL manual, we strongly suggest that if

you refer to existing Informix documentation and tutorials downloadable fromthere web site, and books about 4gl, like:

Informix Unleashed, (ISBN 0672306506) complete book in HTML format

about Informix products, by John McNally. You will find several complete

chapters about 4GL language there, including chapters on Informix database

servers. You will also learn there that "To develop with a 4gl, the developer

does not have to be an expert programmer".
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(I have asked the author for permission to include his book in Aubit 4GLdistribution, but received no answer)

The rest of this page will serve more like quick and dirty crash course to give

you some idea how the I4GL look like, as the language. For A4GL extensions.please refer to the appropriate sections of this manual.

Summary:

To learn I4GL, refer to Informix manuals for Informix-4GL version 7.3(http://www.informix.comor direct links toInformix 4gl by

example,Informix 4gl concepts and use,Informix 4gl Reference

Manual- please remember that exact locations can change, and if they do,

use search function on Informix web site to find new locations of this

documents), and third-party books To learn about A4GL extensions, read this manual To get some idea about how I4GL looks like, and get some idea about

combined I4GL and A4GL functionality, continue reading this page

To get 4GL code examples, go tohttp://www.informix.com/idnand lookfor Example application, or download one of GNU 4GL programs

fromhttp://www.falout.com

2) Short, quick-and-dir ty, general i ntro to x4GL

4GL Programs Structure of a program DATABASE section GLOBALS section Functions MAIN block DEFINE section 4GL Commands

4GL Programs

A 4gl program consists of a series of modules and forms. Each 4gl module cancontain functions and reports and each program must contain exactly one 'main'

section and must end in a .4gl extension. C modules can also be included inprograms
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Structure of a program

database section

globals section

function/report/main block

.

.

.

.

function/report/main block

DATABASE section

This section is optional and is of the format :

DATABASE database-name

The database name is actually the DATA SOURCE NAME (DSN) from theODBC drivers.

GLOBALS section

This optional section allows you to define variables which are accessible to all

modules. There is normally a single file (typically called 'globals.4gl') where

variables are defined. All other modules which need these variables then includethat file using the a global statement .

eg.

globals.4gl

GLOBALSDEFINE a INTEGEREND GLOBALS

module.4gl

GLOBALS "globals.4gl"

Note: In Aubit 4GL the any 'globals' module (containing the GLOBALS / ENDGLOBALS) must be compiled first.

Functions


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A function in 4GL is a set of commands which are executed when called

from another block of code. A function can accepts parameters and can return

values.

A function is defined :

FUNCTION function-name ( parameter-list )define-section

commandsEND FUNCTION

Values are returned using the RETURN keyword:

RETURN value

MAIN block

Each program must contain a main section - it is the starting point in any program.

MAIN

define-section

commandsEND MAIN

DEFINE section

This optional section allows you to define variables which may be used

subsequently:

In its simplest form

DEFINE variable_names datatype

or

DEFINE CONSTANT constant_name "Value"DEFINE CONSTANT constant_name Number-Value

More than one variable can be defined as any type in the same statement by

separating the names with a comma:

DEFINE a,b,c INTEGER

Available datatypes are :


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SMALLINT (2 byte integer)

INTEGER (4 byte integer)

CHAR (Single character 'string')CHAR(n) (n character string

MONEYDECIMAL (These are not fully implemented)FLOAT (8 byte floating point number - (C double))

SMALLFLOAT (4 byte floating point number - (C float))DATE (date - number of days since 31/12/1899)

DATETIME

INTERVALBYTETEXT

VARCHAR Unimplemented yet

LIKE tablename.columnname '1RECORD LIKE tablename.* '1

'1 - can only be used when the module has a DATABASE statement These copy the

datatypes directly from the database either for a simple column, or to generate anentire record (see below)

Special datatypes are :

ARRAY [n] OF datatype defines an array

RECORD .. END RECORD defines a record structure

ASSOCIATE ....

These special types are used with the other datatypes.

Arrays

Syntax:

DEFINE vars ARRAY [n] OF datatype

Eg.

DEFINE lv_arr ARRAY[200] OF INTEGER

defines an array of 200 elements each being an integer

Elements of an array are indexed from 1 to the number of elements specified.


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IMPORTANT: NO BOUNDS CHECKS ARE MADE, accessing elements which

are outside those defined (ie n) will result in an error (Usually a core

dump).

Eg

LET lv_arr[1]=1.

LET lv_arr[200]=200LET lv_arr[201]=201 # this will cause a program fault!

Records

Records are structured groups of data, with the entries are separated by commas.

Elements within a record are accessed via the record name '.' element name.

Syntax

DEFINE recordname RECORD

element datatype,

.

.element datatype

END RECORD

Eg.

DEFINE lv_rec RECORDelem1 CHAR(10),

elem2 INTEGER

END RECORD

Defines a record with two elements.

Eg.

LET lv_rec.elem1="string1"

Record may also be nested and used in conjunction with arrays.

The following are all therefore valid:

DEFINE lv_record ARRAY[20] OF RECORD

elem1 CHAR(20),


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elem2 INTEGER

END RECORD

DEFINE lv_record RECORD

a ARRAY[200] of INTEGER,b CHAR(20)

END RECORD

DEFINE lv_record RECORDsubrecord1 RECORD

elem1 CHAR(10),

elem2 INTEGER

END RECORD,subrecord2 RECORD

elem2 DATEEND RECORD

END RECORD

ASSOCIATE ARRAYS

Associative arrays allow you to access data from an array using a string as a

subscript rather than an integer. For example:

LET age=40

DISPLAY age

This can be especially useful when dealing with codes and code desciptions:

LET lv_desc="Active"

LET lv_desc="Inactive"LET lv_desc="Running"LET lv_desc="Deleted"

LET lv_state="A"

.

.

DISPLAY lv_desc

(This is for illustration, the data would normally be read from a database!)

To define an associate array:

DEFINE name ASSOCIATE [CHAR] (nc) WITH ARRAY [nx] OF datatype

Where nc is the number of characters to use for the index, and nx is the totalnumber of elements that may be stored.


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PERFORMANCE NOTE:

Internally, associate arrays are stored using hash tables, for performance reasonsalways declare 'nx' larger than is actually required. A factor of two is optimum in

most cases.

Again the datatype used in this form of array may be a RECORD, ARRAY etc.

Eg.

DEFINE lv_asoc1 ASSOCIATE CHAR(10) WITH ARRAY[10] OF INTEGER

DEFINE lv_asoc3 ASSOCIATE (10) WITH ARRAY[10] OF INTEGER

DEFINE lv_asoc2 ASSOCIATE CHAR(10) WITH ARRAY[10] OF RECORDelement1 CHAR(10),

element2 CHAR(20)END RECORD

Constants

Constants are defined using

DEFINE CONSTANT name value

Eg.

DEFINE CONSTANT max_num_vars 30DEFINE CONSTANT err_string "There is an error"

IF num_vars>max_num_vars THENERROR err_string

END IF

It is also possible to use constants in any subsequent define sections:

DEFINE CONSTANT num_elems 20DEFINE lv_arr ARRAY [num_elems] OF INTEGER

IF num_vars


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CALL

CASE

CLEARCLOSE

CODECONSTRUCTCONTINUE

CREATECURRENT WINDOW

DECLARE

DISPLAYDROPSERROR

EXECUTE

EXIT PROGRAMEXT

FINISHFOR

FOREACHGOTO

HIDE

HIDE OPTIONIFINIT

INPUT

LABELLET

LOAD

LOCATE

MENUMESSAGEMOVE

NEXT FIELD

NEXT OPTIONOPEN

OPENSOPTIONS

OUTPUT

PAUSE SCREENPREPARE

PROMPTREPORTRETURN

RUN


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SET

SET DATABASE

SHOWSHOW OPTION

SLEEPSQLSQLCODE

STARTSTART RPC

STOP RPC

UNLOADWHENEVERWHILE

DEFER

SYNTAXDEFER INTERRUPT

...etc...

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