Book Image

Haskell High Performance Programming

By : Samuli Thomasson
Book Image

Haskell High Performance Programming

By: Samuli Thomasson

Overview of this book

Haskell, with its power to optimize the code and its high performance, is a natural candidate for high performance programming. It is especially well suited to stacking abstractions high with a relatively low performance cost. This book addresses the challenges of writing efficient code with lazy evaluation and techniques often used to optimize the performance of Haskell programs. We open with an in-depth look at the evaluation of Haskell expressions and discuss optimization and benchmarking. You will learn to use parallelism and we'll explore the concept of streaming. We’ll demonstrate the benefits of running multithreaded and concurrent applications. Next we’ll guide you through various profiling tools that will help you identify performance issues in your program. We’ll end our journey by looking at GPGPU, Cloud and Functional Reactive Programming in Haskell. At the very end there is a catalogue of robust library recommendations with code samples. By the end of the book, you will be able to boost the performance of any app and prepare it to stand up to real-world punishment.
Table of Contents (21 chapters)
Haskell High Performance Programming
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Interpreting GHC's internal representations


The first internal representation in GHC is Core, the second one is STG, and the third one Cmm. Both Core and STG are very functional, while Cmm is an imperative language which resembles C a lot. In this section we will learn to read GHC Core and to spot possible performance problems that might otherwise be hard to spot.

Reading GHC Core

Core is the intermediate language within GHC. Nearly all optimizations GHC does are only program transformations from Core to Core. Reading Core is pretty straightforward for anyone who has read Haskell. For the most part, Core is just let bindings, pattern matches, and function applications. The challenge is in naming conventions, because Core can be quite a noisy code. Following this is a (recursive) function definition in Core (with added line numbering):

1 Rec {
2 foo_rjH
3 foo_rjH =
4   \ ds_d1ya ->
5     case ds_d1ya of wild_X5 { I# ds1_d1yb ->
6     case ds1_d1yb of _ {
7       __DEFAULT ->
8     ...