View source for Software:Comparison of Pascal and Delphi

{{Short description|Programming language}}

{{ProgLangCompare}}
{{use mdy dates|date=April 2023}}
Devised by [[Biography:Niklaus Wirth|Niklaus Wirth]] in the late 1960s and early 1970s, [[Pascal (programming language)|Pascal]] is a [[Programming language|programming language]]. Originally produced by [[Company:Borland|Borland]] Software Corporation, Embarcadero Delphi is composed of an IDE, set of standard libraries, and a Pascal-based language commonly called either [[Object Pascal]], Delphi Pascal, or simply 'Delphi' (Embarcadero's current documentation refers to it as 'the Delphi language (Object Pascal)'<ref>{{Cite web|url=http://docwiki.embarcadero.com/RADStudio/XE2/en/Delphi_Reference|title = Delphi Reference - RAD Studio XE2}}</ref>). Since first released, it has become the most popular commercial Pascal implementation.

While developing Pascal, Wirth employed a [[Bootstrapping (compilers)|bootstrapping]] procedure in which each newer version of the Pascal compiler was written and compiled with its predecessor. Thus, the 'P2' compiler was written in the dialect compilable by 'P1', 'P3' in turn was written in 'P2' and so on, all the way till 'P5'. The 'P5' compiler implemented Pascal in its final state as defined by Wirth, and subsequently became standardised as 'ISO 7185 Pascal'.

The Borland dialect, like the popular [[UCSD Pascal]] before it, took the 'P4' version of the language as its basis, rather than Wirth's final revision. After much evolution independent of Standard Pascal, the Borland variant became the basis for Delphi. This page goes over the differences between Delphi and Standard Pascal. It does ''not'' go into Delphi-specific extensions to the language, which are numerous and still increasing.

== Exclusive features ==
Following features are mutually exclusive.
The Standard Pascal implementation is not accepted by Delphi and vice versa, the Delphi code is not acceptable in Standard Pascal.

=== Modulo with negative dividend ===
Standard Pascal has a Euclidean-like definition of the [[Modulo#In programming languages|<syntaxhighlight lang="pascal" inline>mod</syntaxhighlight> operator]] whereas Delphi uses a truncated definition.

=== Nested comments ===
Standard Pascal requires that the comment delimiters <syntaxhighlight lang="pascal" inline>{</syntaxhighlight> and the bigramm <syntaxhighlight lang="pascal" inline>(*</syntaxhighlight>, as well as <syntaxhighlight lang="pascal" inline>}</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>*)</syntaxhighlight> are synonymous to each other.<ref name="gpc_comments"/>
In Delphi, however, a block comment started by <syntaxhighlight lang="pascal" inline>{</syntaxhighlight> ''must'' be closed with a <syntaxhighlight lang="pascal" inline>}</syntaxhighlight>.<ref name="moore"/>
The bigramm <syntaxhighlight lang="pascal" inline>*)</syntaxhighlight> will only close any comment that started with <syntaxhighlight lang="pascal" inline>(*</syntaxhighlight>.<ref name="moore"/>
This scheme allows for ''nested'' comments at the expense of compiler complexity.

=== Procedural data types ===
The way procedures and functions can be passed as parameters differs:
Delphi requires explicit procedural types to be declared where Standard Pascal does not.<ref name="reagan"/>
{| class="wikitable" style="margin: auto;"
|+ comparison procedural data types
|-
! Standard Pascal !! Delphi
|- style="vertical-align:bottom"
| <syntaxhighlight lang="pascal" highlight="3,4" style="font-size:85%">
program proceduralDataType(output);

	{ `printYIntersect` has one procedural parameter: }
	procedure printYIntersect(function f(x: real): real);
		begin
			writeLn(f(0.0));
		end;
	{ Standard Pascal does not have procedural “pointers.” }
	function f(x: real): real;
		begin
			f := cos(x);
		end;
	{ ─── MAIN ───────────────────────────────────────────── }
	begin
		printYIntersect(f);
	end.
</syntaxhighlight>
| <syntaxhighlight lang="delphi" highlight="1-4" style="font-size:85%">
type
	TFunc = function(x: real): real;

procedure printYIntersect(f: TFunc);
	begin
		writeLn(f(0.0));
	end;

function f(x: real): real;
	begin
		f := cos(x);
	end;
// ─── MAIN ─────────────────────────────────────────────
begin
	printYIntersect(@f);
end.
</syntaxhighlight>
|}

=== Conversion of newline characters ===
Various computer systems show a wide variety how to indicate a newline.
This affects the internal representation of <syntaxhighlight lang="pascal" inline>text</syntaxhighlight> files which are composed of a series of “lines”.
In order to relieve the programmer from any associated headaches, Standard Pascal mandates that ''reading'' an “end-of-line character” returns a single space character.
To distinguish such an “end-of-line” space character from a space character that is actually genuine payload of the line, <syntaxhighlight lang="pascal" inline>EOLn</syntaxhighlight> becomes <syntaxhighlight lang="pascal" inline>true</syntaxhighlight>.

Delphi does not show this behavior.
Reading a newline will return whatever character sequence represents a newline on the current host system, for example two <syntaxhighlight lang="delphi" inline>char</syntaxhighlight> values <syntaxhighlight lang="delphi" inline>chr(13)</syntaxhighlight> (carriage return) plus <syntaxhighlight lang="delphi" inline>chr(10)</syntaxhighlight> (line feed).<ref name="moore"/>

== Additional or missing features ==
Following features are present or missing in either language.

=== Global <syntaxhighlight lang="pascal" inline>goto</syntaxhighlight> ===
Standard Pascal permits a <syntaxhighlight lang="pascal" inline>goto</syntaxhighlight> to any <syntaxhighlight lang="pascal" inline>label</syntaxhighlight> defined in scope.
In Delphi a <syntaxhighlight lang="delphi" inline>goto</syntaxhighlight> must be within the current routine, i. e. may not leave the <syntaxhighlight lang="delphi" inline>begin … end</syntaxhighlight>-frame.<ref name="moore"/>
<syntaxhighlight lang="pascal" highlight="6,7">program jumpAround;
	label
		999;
	procedure foo;
		begin
			{ This is not permitted in Delphi: }
			goto 999;
		end;
	begin
		foo;
		999: ;
	end.</syntaxhighlight>

=== Buffer variables ===
Delphi does not support buffer variables and associated standard routines <syntaxhighlight lang="pascal" inline>get</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>put</syntaxhighlight>.<ref name="moore"/>
<syntaxhighlight lang="pascal" highlight="5,6,15,19">program copy(input, output);
	begin
		while not EOF(input) do
		begin
			{ Copy file buffers. Not supported by Delphi }
			output↑ := input↑;
			
			{ Input↑ contains a space if a new-line occurred. }
			if EOLn(input) then
			begin
				writeLn(output);
			end
			else
			begin
				put(output);
			end;
			
			{ Advance reading cursor. }
			get(input);
		end;
	end.</syntaxhighlight>

=== Discriminated variant record allocation ===
In Standard Pascal allocating memory for a variant <syntaxhighlight lang="pascal" inline>record</syntaxhighlight> may indicate a specific variant.
This allows implementations to allocate the least amount of ''really'' necessary memory.
Delphi does not support this.<ref name="moore"/>
<syntaxhighlight lang="pascal" highlight="13,14">program variantRecord;
	type
		sex = (female, male);
		clothingMeasures = record
				girth: real;
				case gender: sex of
					female: (underbust: real);
					male: ( );
			end;
	var
		size: clothingMeasures;
	begin
		{ NB: No space allocated for `underbust`. }
		new(size, male);
	end.</syntaxhighlight>

=== Temporary files ===
In Delphi any file must be backed by a file in the file system.
That means any <syntaxhighlight lang="delphi" inline>file</syntaxhighlight> needs to be associated with a file name with Delphi's <syntaxhighlight lang="delphi" inline>assign</syntaxhighlight> procedure.
In contrast, Standard Pascal is usable without file names.
The following will produce a run-time error with Delphi.<ref name="moore"/>
<syntaxhighlight lang="pascal">program temporaryFile(output);
	var
		FD: text;
	begin
		rewrite(FD);
		writeLn(FD, 'Hello world!');
	end.</syntaxhighlight>

=== Packing ===
Delphi does not implement the standard procedures <syntaxhighlight lang="pascal" inline>pack</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>unpack</syntaxhighlight>.<ref name="moore"/>
Regardless, transferring data between packed and unpacked data types is an easy feat, although the implementation might not be as efficient as a compiler vendor supplied implementation would be.

=== Missing default <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width ===
Delphi does not associate the data type <syntaxhighlight lang="pascal" inline>Boolean</syntaxhighlight> with a default width if specified as <syntaxhighlight lang="pascal" inline>write</syntaxhighlight>/<syntaxhighlight lang="pascal" inline>writeLn</syntaxhighlight> parameters.<ref name="moore"/>
Delphi demonstrates the behavior as usual for character-strings.

=== Overloading ===
Delphi permits overloading routines.
In Standard Pascal identifiers must be unique in every block.
<syntaxhighlight lang="delphi">function f(x: integer): real;
begin
	result := sin(x);
end;

function f(x: real): real;
begin
	result := cos(x);
end;
// ─── MAIN ─────────────────────────────────────────────
begin
	// Note the different data types.
	writeLn(f(3));
	writeLn(f(3.0));
end.</syntaxhighlight>

=== Default parameter values ===
Delphi permits default parameters.

== Peculiar implementation characteristics ==
=== Standard <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width ===
In Pascal, if the destination file is a <syntaxhighlight lang="pascal" inline>text</syntaxhighlight> file, the parameters to <syntaxhighlight lang="pascal" inline>write</syntaxhighlight>/<syntaxhighlight lang="pascal" inline>writeLn</syntaxhighlight> have an implemention-defined default total width.
In Delphi, for <syntaxhighlight lang="delphi" inline>integer</syntaxhighlight> values this is simply <syntaxhighlight lang="delphi" inline>1</syntaxhighlight>.
That means always the least amount of space is occupied.<ref name="moore"/>
Other compilers have shown default widths of, for example, <syntaxhighlight lang="pascal" inline>20</syntaxhighlight> allowing for a fine tabular look at no cost of extra code.
{| class="wikitable" style="margin: auto;"
|+ comparison default <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width
|-
! colspan="2" | source code fragment
|-
| colspan="2" | <syntaxhighlight lang="pascal">writeLn(1);
writeLn(23456789);</syntaxhighlight>
|-
! colspan="2" | produces in
|-
! Standard Pascal ([[Software:GNU Pascal|GPC]]) !! Delphi
|-
| <syntaxhighlight lang="text">          1
   23456789</syntaxhighlight>
| <syntaxhighlight lang="text">1
23456789</syntaxhighlight>
|}

== References ==
<references>
<ref name="gpc_comments">{{cite web
| title           = The GNU Pascal Manual
| first1          = Jan-Jaap
| last1           = van der Heijden
| first2          = Peter
| last2           = Gerwinski
| first3          = Frank
| last3           = Heckenbach
| first4          = Berend
| last4           = deBoer
| first5          = Dominik
| last5           = Freche
| first6          = Eike
| last6           = Lange
| first7          = Peter
| last7           = Lewis
| display-authors = etal
| at              = A QuickStart Guide from Borland Pascal to GNU Pascal
| url             = https://www.GNU-Pascal.de/gpc/Comments.html#Comments
| access-date     = 2023-04-24
}}</ref>
<ref name="reagan">{{cite web
| title           = Pascal Standards FAQ
| at              = Comparison of Borland Pascal to the Pascal standards
| first           = John
| last            = Reagan
| date            = 1995-04-03
| url             = http://Pascal-Central.com/extpascal.html#anchor-6
| archive-url     = https://web.archive.org/web/20210928162340/http://pascal-central.com/extpascal.html#anchor-6
| archive-date    = 2021-09-28
}}</ref>
<ref name="moore">{{cite web
| title           = Standard Pascal FAQ
| at              = Q. What are the differences between Borland Delphi and the ISO 7185 standard?
| first           = Scott
| last            = Moore
| date            = 2022-12-02
| url             = https://www.MooreCAD.com/standardpascal/pascalfaq.html#Q.%20What%20are%20the%20differences%20between%20Borland%20Del
| access-date     = 2023-04-24
}}</ref>
</references>

== Further reading ==
* Kathleen Jansen and [[Biography:Niklaus Wirth|Niklaus Wirth]]: ''PASCAL - User Manual and Report.'' Springer-Verlag, 1974, 1985, 1991, {{ISBN|0-387-97649-3}}, {{ISBN|0-387-90144-2}}, and {{ISBN|3-540-90144-2}} [https://web.archive.org/web/20050314152247/http://www.cs.inf.ethz.ch/~wirth/books/Pascal/]
* Niklaus Wirth: ''The Programming Language Pascal.'' Acta Informatica, 1, (Jun 1971) 35–63
* ISO/IEC 7185: ''Programming Languages - PASCAL.'' [http://www.moorecad.com/standardpascal/]
* Doug Cooper: ''Standard Pascal: User Reference Manual.'' W. W. Norton & Company, 1983, {{ISBN|0-393-30121-4}}, {{ISBN|978-0-393-30121-2}}

== External links ==
* [https://www.moorecad.com/standardpascal/ The ISO 7185 Pascal web site]
* [https://www.StandardPascal.org/standards.html Pascal standards documents]

{{Pascal programming language family}}

{{DEFAULTSORT:Pascal and Delphi comparison}}
[[Category:Pascal programming language family]]

{{Sourceattribution|Comparison of Pascal and Delphi}}