Lenses for the Mere Mortal: PureScript Edition

Description

Lens libraries, such as Haskell’s Control.Lens or PureScript’s Data.Lens, have the reputation of being hard to learn, or at least hard to learn well. That’s not to say that lots of people haven’t learned them. Many have. But many others have had a hard time, me included. This book teaches lenses differently. I don’t claim I’ve found the single best way to teach them, just that this way is worth a try, whether you’re learning lenses for the first time or you’ve bounced off some other tutorial that didn’t work for you. Table of Contents......Page 3 Introduction......Page 6 Optics are useful......Page 7 Why are optics notoriously confusing?......Page 9 This book's approach......Page 10 About the cover......Page 11 Change log......Page 12 Thanks for the help......Page 13 Tuples and records (lenses for product types)......Page 14 Tuples......Page 15 Records......Page 16 Composition exercise......Page 18 Types......Page 19 Composition exercise two......Page 22 Lens laws......Page 24 What now?......Page 25 A custom implementation......Page 26 At.at......Page 28 Types......Page 30 Composing At lenses......Page 32 What now?......Page 35 Optics and refactoring (optional)......Page 37 Architecture......Page 38 Optics......Page 40 Exercise......Page 42 My solution......Page 43 What now?......Page 45 Working with all the values......Page 46 view......Page 48 Focusing on individual values......Page 50 Composing traversals......Page 51 What now?......Page 56 ix, at, and Map......Page 57 Types......Page 59 Composition......Page 60 What now?......Page 61 Using prisms......Page 62 Making a prism......Page 64 Prism laws......Page 66 Value constructors with more than one argument......Page 67 Types......Page 69 Composing prisms......Page 70 Prisms aren't just for sum types (exercises)......Page 75 What now?......Page 76 Miscellaneous other optics......Page 77 Appendices......Page 78 class At......Page 79 Traversal......Page 80 class Index......Page 81 Prism......Page 82 Prism