Chapter 1 ( Introduction )

    An intermediate knowledge of Haskell is required. We will make heavy use of monads and transformers without pause for exposition. If you are not familiar with monads, applicatives and transformers then it is best to learn these topics before proceeding. Conversely if you are an advanced Haskeller you may notice the lack of modern techniques which could drastically simplify our code. Instead we will shy away from advanced patterns since the purpose is to instruct in LLVM and not Haskell programming. Whenever possible we will avoid cleverness and just do the “stupid thing”.

    The overall goal of this tutorial is to progressively unveil our language, describing how it is built up over time. This will let us cover a fairly broad range of language design and LLVM-specific usage issues, showing and explaining the code for it all along the way, without overwhelming you with tons of details up front.

    It is useful to point out ahead of time that this tutorial is really about teaching compiler techniques and LLVM specifically, not about teaching modern and sane software engineering principles. In practice, this means that we’ll take a number of shortcuts to simplify the exposition. If you dig in and use the code as a basis for future projects, fixing these deficiencies shouldn’t be hard.

    • Chapter #1: Introduction to the Kaleidoscope language, and the definition of its Lexer - This shows where we are going and the basic functionality that we want it to do. LLVM obviously works just fine with such tools, feel free to use one if you prefer.

    • Chapter #2: Implementing a Parser and AST - With the lexer in place, we can talk about parsing techniques and basic AST construction. This tutorial describes recursive descent parsing and operator precedence parsing. Nothing in Chapters 1 or 2 is LLVM-specific, the code doesn’t even link in LLVM at this point. :)

    • Chapter #5: Extending the Language: Control Flow - With the language up and running, we show how to extend it with control flow operations (if/then/else and a ‘for’ loop). This gives us a chance to talk about simple SSA construction and control flow.

    • Chapter #7: Extending the Language: Mutable Variables - This chapter talks about adding user-defined local variables along with an assignment operator. The interesting part about this is how easy and trivial it is to construct SSA form in LLVM: no, LLVM does not require your front-end to construct SSA form!

    This tutorial will be illustrated with a toy language that we’ll call Kaleidoscope (derived from “meaning beautiful, form, and view” or “observer of beautiful forms”). Kaleidoscope is a procedural language that allows you to define functions, use conditionals, math, etc. Over the course of the tutorial, we’ll extend Kaleidoscope to support the if/then/else construct, a for loop, user defined operators, JIT compilation with a simple command line interface, etc.