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Soar with Haskell

You're reading from   Soar with Haskell The ultimate beginners' guide to mastering functional programming from the ground up

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Product type Paperback
Published in Dec 2023
Publisher Packt
ISBN-13 9781805128458
Length 418 pages
Edition 1st Edition
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Author (1):
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Tom Schrijvers Tom Schrijvers
Author Profile Icon Tom Schrijvers
Tom Schrijvers
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Table of Contents (23) Chapters Close

Preface 1. Part 1:Basic Functional Programming FREE CHAPTER
2. Chapter 1: Functions 3. Chapter 2: Algebraic Datatypes 4. Chapter 3: Recursion 5. Chapter 4: Higher-Order Functions 6. Part 2: Haskell-Specific Features
7. Chapter 5: First-Class Functions 8. Chapter 6: Type Classes 9. Chapter 7: Lazy Evaluation 10. Chapter 8: Input/Output 11. Part 3: Functional Design Patterns
12. Chapter 9: Monoids and Foldables 13. Chapter 10: Functors, Applicative Functors, and Traversables 14. Chapter 11: Monads 15. Chapter 12: Monad Transformers 16. Part 4: Practical Programming
17. Chapter 13: Domain-Specific Languages 18. Chapter 14: Parser Combinators 19. Chapter 15: Lenses 20. Chapter 16: Property-Based Testing 21. Index 22. Other Books You May Enjoy

Call by Need

Haskell’s evaluation strategy is called Call by Need or lazy evaluation. It is quite similar to Call by Name in that it only evaluates work that is needed for the result of the computation. At the same time, it avoids the main problem of Call by Name: it does not duplicate any work.

Sharing

The way in which lazy evaluation avoids duplication is known as sharing, or sometimes also as memoization. Instead of duplicating work, the work is shared, and when the work is performed once, all who share it can use the work’s results without redoing them.

Conceptually, we model sharing the work by using let binding:

  (\x -> x + x) (sin 1.0)
↣ let w = sin 1.0
   in w + w

To evaluate the sum in the body of the let binding, we first have to evaluate its left operand. As this operand is a let bound variable w, we consult the binding. The binding shows that the variable is bound to a reducible expression. Hence, we reduce...

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