Differences between the languages Borland Delphi

Because Borland Delphi is a widely used version of Pascal, it is useful to compare the two languages. Note that here are presented only the differences between Borland Delphi and the basic ISO 7185 standard. Undiscussed are any extensions provided by Borland Delphi. In other words, this section answers the question "why doesn't my standard Pascal program run under Borland Delphi?", and perhaps "what can I write in Borland Delphi that will also be compatible with the ISO 7185 standard?".

1. Procedures and functions may not appear as parameters (it is true that it can be done, but a non-standard syntax must be used).

2. Goto statements cannot reference targets outside procedure/function bodies (so called "intraprocedural gotos").

3. No file buffer variable handling. Standard Pascal has file "buffer variables", and "get" and "put" procedures to operate on them. This functionality is not present in Borland Delphi.

4. No "sized" dynamic variable allocation. Given a variant record, the size of a particular variant cannot be specified as per the standard. I.e., the following statement is invalid:

new(p, t)

Where t is a variant record tag type.

5. The functions "pack" and "unpack" are not implemented.

6. { and (*, } and *) are not synonyms of each other as required by the standard. Ie.:

{ comment *)

is not valid in Borland Delphi (Delphi uses the scheme of allowing the different comment types to indicate nested comments).

7. It is not possible to construct a standard program without compiler directives. At minimum:

{$APPTYPE CONSOLE}

is required.

8. Does not replace eoln with space as the standard requires. When reading through the end of a line, the eoln character is supposed to be replaced with a space in ISO 7185. Instead, reading through eoln in Borland Delphi gives the character code for carriage return (13), followed by line feed (10).

9. Numbers and booleans are not printed out in their "default" field widths, but are printed in the minimum amount of space. For example:

write('>', 5, '<');

Outputs:

>5<

in Delphi, but:

> 5<

(spaces depend on compiler integer width) in ISO 7185.

For booleans:

write('>', true, '<');

outputs:

>true<

in Delphi, but:

> true<

In ISO 7185.

Brief description

Wirth's intention was to create an efficient language (regarding both compilation speed and generated code) based on so-called structured programming, a concept which had recently become popular. Pascal has its roots in the Algol 60 language, but also introduced concepts and mechanisms which (on top of Algol's scalars and arrays) enabled the programmer to define his or her own complex (structured) datatypes, and also made it easier to build dynamic and recursive data structures such as lists, trees and graphs. Important features included for this were records, enumerations, subranges, dynamically allocated variables with associated pointers, and sets. To make this possible and meaningful, Pascal has a strong typing on all objects, which means that one type of data cannot be converted or interpreted as another without explicit conversions. Similar mechanisms are standard in many programming languages today. Other languages that influenced Pascal's development were COBOL, ALGOL 68, Simula 67, and Wirth's own Algol-W .

Pascal, like many scripting languages of today (but unlike most languages in the C-family), allows nested procedure definitions to any level of depth, and also allows most kinds of definitions and declarations inside procedures and functions. This enables a very simple and coherent syntax where a complete program (or unit) is syntactically nearly identical to a single procedure or function (except for the keyword itself, of course).