Free Pascal Compiler (FPC) is a compiler for the closely related programming-language dialects Pascal and Object Pascal. It is free software released under the GNU General Public License, with exception clauses that allow static linking against its runtime libraries and packages for any purpose in combination with any other software license.

It supports its own Object Pascal dialect, as well as the dialects of several other Pascal family compilers to a certain extent, including those of Turbo Pascal, Delphi, and some historical Macintosh compilers. The dialect is selected on a per-unit (module) basis, and more than one dialect can be used per program.

It follows a write once, compile anywhere philosophy and is available for many CPU architectures and operating systems (see Targets). It supports inline assembly language and includes an internal assembler capable of parsing several dialects such as AT&T and Intel style.

Separate projects exist to facilitate developing cross-platform graphical user interface (GUI) applications, the most prominent one being the Lazarus integrated development environment (IDE). 

Supported dialects
Initially, Free Pascal adopted the de facto standard dialect of Pascal programmers – Borland Pascal – but later on adopted Delphi. From version 2.0 on, Delphi compatibility has been continuously implemented or improved.

The project has a compilation mode concept, and the developers made it clear that they would incorporate working patches for the standardized dialects of the American National Standards Institute (ANSI) and International Organization for Standardization (ISO) to create a standards-compliant mode.

A small effort has been made to support some of the Apple Pascal syntax to ease interfacing to the Classic Mac OS and macOS. Since the Apple dialect implements some standard Pascal features that Turbo Pascal and Delphi omit, Free Pascal is a bit more ISO-compatible than these.

The 2.2.x release series did not significantly change the dialect objectives beyond roughly Delphi 7 level syntax, instead aiming for closer compatibility. A notable exception to this was the addition of support for generics to Free Pascal in version 2.2.0, several years before they were supported in any capacity by Delphi.

As of 2011, several Delphi 2006-specific features were added in the development branch, and some of the starting work for the features new in Delphi 2009 (most notably the addition of the UnicodeString type) was completed. The development branch also features an Objective-Pascal extension for Objective-C (Cocoa) interfacing.

As of version 2.7.1, Free Pascal implemented basic ISO Pascal mode, though many things such as Get and Put procedure and file-buffer variable concept for file handling were still absent.

As of version 3.0.0, ISO Pascal mode is fairly complete, with one remaining bug that has since been fixed in the trunk branch. It has been able to compile standardpascal.org's P5 ISO Pascal compiler with no changes. 

Integrated development environments
Like most modern compilers, Free Pascal can be used with an integrated development environment (IDE). Besides independent IDEs there are also plugins to various existing IDEs 

• Free Pascal has its own text-mode IDE resembling Turbo Pascal's IDE. It is made using the Free Vision framework (also included with Free Pascal), a Turbo Vision clone. In addition to many features of the Turbo Pascal IDE, it has code completion and support for multiple help file formats (HTML, Microsoft Compiled HTML Help (CHM), Information Presentation Facility (IPF). Instead of using command line tools, the IDE uses its own embedded compiler, based on the same source as the command line compiler and debugger (using libgdb or GDBMI) to provide its functionality.
• Lazarus is the most popular IDE used by Free Pascal programmers. It looks and feels similar to the Delphi IDE, and can be used to create console and graphical applications, Windows services, daemons, and web applications. Lazarus provides a cross-platform user interface framework, called Lazarus Component Library (LCL). Graphical applications created with LCL can be ported to another platform via recompiling or cross compiling.
• Dev-Pascal is a free Windows-only IDE for Free Pascal and GNU Pascal, with no further development following the 2004 FPC version and the 2005 GPC version.

Specifications

Industry :

Information technology