Pascual: A self-hosting Pascal compiler

Pascual is a Pascal compiler by Jacobo Tarrío. Pascual is written in Pascal and can compile itself.

Pascual generates C code that can then be compiled into an executable file.

Features

Pascual currently supports a subset of the Turbo Pascal 3 syntax and features:

• Boolean, integer, real, char, and string; enumerated types, subranges; arrays, records, pointers, and sets; text and binary files.
• Type definitions, variable definitions, untyped constant definitions, typed constant definitions.
• Functions and procedures, pass by value, pass by reference, and pass by const reference.
  • Missing nested functions and procedures.
  • Missing parameterized array bounds.
• While, repeat until, for, if, case.
  • Missing label ranges and multiple labels for case.
  • Missing goto.
• Write, writeln, read, readln, str, val.
• Compiler directives:
  • {$I name.pas}: include the file name.pas
  • {$I-}, {$I+}: disable or enable checking for an error after every I/O operation (enabled by default)
  • {$R-}, {$R+}: disable or enable bounds checking (enabled by default)

Objectives

The first objective with Pascual is to make it comparable to Turbo Pascal 3. The next objective is to introduce compilation units and make it comparable to Turbo Pascal 5. A stretch objective is to introduce Object Pascal features and make it comparable to Turbo Pascal 7.

Pascual compiles to the C programming language. A stretch objective is to add an assembly language backend and so turn it into a “real” compiler, but it is expected to retain the ability to compile to C.

Pascual is a platform for learning how to write a compiler; as such, even though I hope to make it as complete as possible, it may always be a bit of a toy.

How to build

You need Make and a C compiler to build Pascual. I use GCC but Clang works as well. I develop Pascual in Linux, but it should also compile in MacOS.

To build Pascual, type the following command:

$ make

Pascual should be available on the dist subdirectory.

How to use

There are two executables: pascual and pascualc. The pascual executable is the Pascal-to-C converter; pascualc is a shell script that uses pascual to implement a regular compiler that outputs an executable file.

(The pascualc script will, one day, be removed, and pascual will be able to call the C compiler itself.)

To convert a Pascal program to C, run pascual like this:

$ dist/pascual input.pas -o output.c

If you don't specify an output file name, it will be the same as the input file name, with its .pas extension replaced with .c.

You can also read from stdin and write to stdout by using - (hyphen) as the input or output file names.

To compile to an executable, run pascualc like this:

$ dist/pascualc input.pas -o output

If you don't specify an output file name, it will be the same as the input file, with its .pas extension removed.

You can also convert a program to C and then compile it afterwards with your C compiler, by doing it like this:

$ dist/pascual input.pas -o output.c
$ cc -Idist -Ldist -o output output.c -lpascual

What it looks like

I've seen so many programs that convert a language to some other language, and they never show examples. Not Pascual: you can see some examples, with their conversions to C, in the examples subdirectory.

Documentation

I just started writing a manual. When I finish it, it's going to be awesome.

In the meantime, you can look at the examples subdirectory to see what kinds of features are supported and how they are used.

License

Pascual, its runtime library, examples, and tests are made available under the terms of the Apache License 2.0.