Haskell

1. Dan Johnson Haskell

2. History in a Nutshell • Functional language that started development in 1987. • Committee designed language • Pure and Lazy • Compiled or Interpreted • Named after Haskell Curry (who has nothing to do with the language itself)

3. The Goals of Haskell • It should be suitable for teaching, research, and applications, including building large systems. • It should be completely described via the publication of a formal syntax and semantics. • It should be freely available. • It should be usable as a basis for further language research. • It should be based on ideas that enjoy a wide consensus. • It should reduce unnecessary diversity in functional programming languages.

4. Prelude • Contains a large number of functions for basic operations and list manipulation. • Loaded automatically when ghci is started

5. Everything has a type! • Everything is considered to be “of a type”. • A functions type is determined by its return type. • The :: literally means “is of the type”. • Groups of similar types are classified into Typeclasses.

6. More about types! • Type Inference • Haskell will evaluate the parameters to this function and determine that... • Generally considered bad practice to rely on type inference

7. Lists and Tuples • Lists function the same way as in Racket. • Tuples are fixed length types that can contain multiple elements of different types. • By combining lists and tuples, you can create complex and powerful data structures

8. F.. Functions. • Two parts: declaration and definition • Line 34 uses type variables to make the function polymorphic. • Line 35 uses some of the list functions built into prelude

9. Curried Functions • Two ways to pass multiple parameters to a function: • By using a tuple as the parameter • By defining the function as a curried function • Most multi-parameter functions are curried functions

10. Higher Order Functions • Any function that returns a function as its result or accepts a function as a parameter • All curried functions are Higher Order functions because their return type is technically a function

11. Polymorphic Functions • Any function that uses type variables (and only type variables) is considered to be a polymorphic function. • Polymorphic functions are easy to create • Type inference automatically defines polymorphic types when applicable. • Allow for one function to cover a broad range of types • Most functions in the Prelude are polymorphic functions

12. If .. Then .. vs Guards If .. Then .. Guards • Syntactically similar to most languages • No “else if” statement, must be done with nested ifs • Written more as a mathematician would write a case structure • More readable, less code to write

13. Recursion • Is at the core of Haskell because it is so prevalent in mathematics • Simply recall the function with different parameters in the function

14. Object Oriented Design

15. Lazy Evaluation • Expressions are only evaluated as much as required to produce the final result. • What does this mean? • Why is it important? • Where can we use it?

16. Purity • Pure languages are said to e languages without side effects • What is a side effect? • Is a pure language even possible? • What are the benefits of purity? • What are the cons of purity?

17. Hangman