Projet_fin_module_compilateurs

This project uses a very original approach to parse a subset of the Pascal language, and covers all the aspects necessary for generating an X86 assembly program. The project is a bit 'dated', but the way recursive descent parsing was implemented is worth a look.

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README

Pascal to x86 Assembly Compiler (1994) – an original trick for ε-rules

Author: mzeus65
Year: 1994, republished 2026
License: GPL v3

The short story

In 1994, I wrote a Pascal compiler for my "Languages and Compilers" class.
My teacher gave me the highest grade, but dismissed it with: "We can also read books" – implying I had just copied a textbook.

He never really looked at my code.

The truth: my recursive descent parser handles empty derivations (ε-rules) using two booleans per function:

check_ok : the rule succeeded (even with zero tokens consumed)
check_e : the rule derived empty

This makes the grammar extremely easy to modify. No FIRST/FOLLOW, no left factoring, no complicated lookahead.
I've never seen this trick in any book – then or since.

To this day, no one else in that institute ever completed a working compiler to this level.

What's inside

pro2asm.pas – the main compiler (Turbo Pascal)
fact.lex – example Pascal program (factorial)
pro2asm.exe – precompiled DOS executable

Quick test (if you have Free Pascal or DosBox)

bash

fpc pro2asm.pas
./pro2asm fact.lex

## What I'm asking

I have ADHD and I'm retired. My memory of the details is fading.
I just want people who know compilers to take a quick look at pro2asm.pas and tell me: is this two-boolean trick known, or is it genuinely original?

Any honest feedback is welcome.

– mzeus65

Live chat for Free Pascal, Lazarus, Delphi and every Pascal programmer.