(comments are in French)
It was amazing : the full compiler was around 650 lines of code while only using Parsec as a third party library and was able to compile correctly at the first successful compilation. Compiling to LLVM (as text, I didn't used any library for code generation) using monads and Text-Lazy was also pretty pleasant.
My only deception was to be unable to use GADTs : these are awesome but so hard to use with a parser.
One rather minor question: Is writing comments or even code in the local language still common in France? Afaik, in most European countries the CS courses are taught in English.
Anyway, I write all of my "public code" in English. The audience is different.
Not really. You only write stuff in English if it intended for publication like papers and stuff.
Anyway, I was dissatisfied of that. GADTs are awesome to add some "proofness" to a type checker.