1 / 10

Functional Programming

Functional Programming. “When I code in C, I feel I'm on a knife-edge of ‘state’ — I focus on statements and what they do. I'm worried about the behaviour of a machine.” - Richard A. O'Keefe. What is Functional Programming?. Programs work by returning values instead of modifying data

tommyv
Download Presentation

Functional Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Functional Programming “When I code in C, I feel I'm on a knife-edge of ‘state’ — I focus on statements and what they do. I'm worried about the behaviour of a machine.” - Richard A. O'Keefe

  2. What is Functional Programming? • Programs work by returning values instead of modifying data • Side-effect free • No variables, no destructive modification of data, no state • LISP is a functional programming language, but it is not pure; it has many imperative features

  3. A Programming Discipline • A description of functional programming reads as a list of things I can’t do! • By restricting code to stateless computations, you make it impossible for certain types of errors to occur • Functional programming methodology will make you a better imperative programmer (Java, C++) • For those times when you absolutely can’t do without state, LISP lets you cheat (I’m about to show you how) • Don’t cheat if you don’t have to

  4. Local Bindings: Variables? (let ((name value)*) body) • Assigns values to names in parallel >(let ((a 5) (b 25)) (+ a b)) 30 • Names with no value default to nil >(let (x y (z 6)) (cons x (cons y z))) (NIL NIL . 6)

  5. Let • Saves you from repeating code/computation (defun profit (volume unit-price unit-cost tax-rate) (let ((revenue (* unit-price volume)) (overhead (* unit-cost volume))) (- revenue (+ overhead (* tax-rate revenue))) )) • Using functional programming style, you should think of these values as immutable (only assigned once) • We’ll learn the truth in a moment…

  6. Let* • The following code has an error: >(let ((a 5) (b (+ a 10))) (* a b)) Error: The variable A is unbound. • Because assignments are in parallel, names in a single let don’t have access to other names in the same let • let* fixes this; it assigns serially: >(let* ((a 5) (b (+ a 10))) (* a b)) 75

  7. Global Bindings • Constants and variables • Global constants cannot have their values changed (defconstant symbol S-expression string-comment) • Global variables can have their values changed, therefore I recommend never using them (defvar symbol S-expression string-comment) • defvar is used to assign an initial value only, not to change a variable value

  8. Boundp • boundp determines if a given name is already assigned >(boundp 'pi) T >(boundp 'Jacob) NIL

  9. Changing State With Setf • This is how you change the value of a variable (setf place value) • The place must be preexisting • Defined using defvar • Defined locally in a let • Place can even be a specific reference in a list, or other structure >(defvar h '(4 5 6 7 8 9)) H >(setf (caddr h) 'NEW) NEW >h (4 5 NEW 7 8 9)

  10. Final Words on Variables • setf is an imperative feature • It’s what you’re used to, so you’ll feel tempted to use it • Go outside your comfort zone: • Every time you feel like using variables, ask yourself if it’s really necessary • Sometimes it is (homework assignments will usually make this clear)

More Related