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The PL/I Programming Language
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PL/1 was developed as an IBM product in the mid 1960's, and was originally named NPL (New Programming Language). The name was changed to PL/1 to avoid confusion of NPL with the National Physical Laboratory in England. If the compiler had been developed outside of the United Kingdom, the name may have remained PL/1.
Until the time this new language was developed, all previous languages had focused on one particluar area of application, such as science, artificial intelligence, or business. PL/1 was not designed to be used in the same way. It was the first large-scale attempt to design a language that could be used in a variety of application areas.
Significant Language Features
PL/1 had the following significant language features:
- PL/I is completely free form and has no reserved keywords.
- It precisely defines it's data types without regard for any hardware.
- PL/I is a block-oriented language, consisting of packages, begin blocks, and statements. This type of structure allows the programmer to produce highly-modular applications.
- PL/I contains control stuctures.
- For example, SELECT...WHEN...OTHERWISE allow logical operations, and DO statements allow units to be executed unconditionally one time, forever, or while a condition is true or until a condition becomes true.
- PL/I supports arrays, structures, unions, arrays of structures or unions, structures or unions of arrays, and combinations thereof.
- PL/I provides four different storage classes: AUTOMATIC, STATIC, CONTROLLED, and BASED. Application objects' data type, representation, nature of use, etc... normally decides the type of storage class used for each.
Areas of Application
PL/1 was used significantly in both business and scientific applications. It was also the main language taught at the University of Michigan Dearborn for a period of time. However, it's popularity has declined in recent years, due to the introduction of newer programming languages.
These are a few of the places were PL/1 was/is used:
- Marathon Oil Company
- Ford Motor Company
Sample Program
Source Code: (Hello World)
HELLO: PROCEDURE OPTIONS (MAIN);
/* A PROGRAM TO OUTPUT HELLO WORLD */
FLAG = 0;
LOOP: DO WHILE (FLAG = 0);
PUT SKIP DATA('HELLO WORLD!');
END LOOP;
END HELLO;
This program was not tested due to unavailablility of a compiler.
This program demonstrates the text output function of the PL/I programming language by displaying the message "Hello world!".
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