Lets use this file for tutorial:

USEFUL LINKS TO LOOK THROUGH:

Lexer and Parser aka scanner and parser
http://caml.inria.fr/pub/docs/manual-ocaml/lexyacc.html


ocaml modul LLVM:
https://llvm.moe/ocaml-3.7/Llvm.html

about llvm :
http://www.cs.cmu.edu/~janh/courses/411/16/lec/26-llvm-slides.pdf

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MAYBE START HERE:
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the ocaml llvm tutorial very detailed : note in chapter 1,2 they do not use the lexer parser tool(yak),
so syntax is not what we need, so skim for ideas and general understanding maybe 
https://llvm.org/docs/tutorial/

this one is looks like one step by step similar to what we should do in code gen:
https://llvm.org/docs/tutorial/OCamlLangImpl3.html