《Haskell Design Patterns》

【实例截图】

【核心代码】

Table of Contents
Preface v
Chapter 1: Functional Patterns – the Building Blocks 1
Higher-order functions 2
Functions as first-class citizens 2
Composing functions 3
Currying functions 3
Currying and composability 4
Decoupling with currying 5
Recursion 5
Non-tail recursion 5
Tail recursion 6
Folding abstracts recursion 6
Types, pattern matching, and polymorphism 7
Algebraic types and pattern matching 7
Recursive types 8
Polymorphism 8
Parametric polymorphism 8
Ad-hoc polymorphism 9
Functions, types, and patterns 13
The strategy pattern 14
The template pattern 14
The iterator pattern 15
Decoupling behavior and modularizing code 15
Lazy evaluation 15
Streams 16
Modeling change with streams 17
Lazy evil 18
Monads 18
Composing monads and structuring programs 20
Summary 21
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Chapter 2: Patterns for I/O 23
I/O as a first class citizen 24
I/O as a functor, applicative, and monad 25
Imperative I/O 25
Lazy I/O 28
The problems with lazy I/O 33
Resource management with bracket 34
Iteratee I/O 36
Iteratee 37
Enumerator 39
Generalized iteratees, enumerators, and enumeratees 40
The iteratee I/O libraries 41
Comparing the three styles of I/O 42
Summary 42
Chapter 3: Patterns of Composition 43
Functor 43
Applicative functor 45
Monad 47
Monad as functor 49
Monad as applicative 50
Sequencing actions with monad and applicative 51
Monads and the bind chain 51
Composing with monads 53
Monad transformers 53
IO in monad stacks 57
Sequence of stack composition 58
Arrows 59
Implementing an arrow 60
Arrow operators 61
Kleisli arrows and monad arrows 63
Why arrows? 64
Summary 65
Chapter 4: Patterns of Folding and Traversing 67
Folding over lists 68
Folding with monadic functions 68
Folding with monoids 69
Foldable 71
Mapping over lists 74
Traversable 75
A Traversable Tree 76
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The traversal and the Iterator pattern 77
Modernizing Haskell 98 78
Lenses 79
Deriving Lens 79
Writing a Lens 81
Composable getters and setters 82
Lens Traversal 83
Lens.Fold 84
The Lens library 84
Summary 85
Chapter 5: Patterns of Type Abstraction 87
Abstracting function types: RankNTypes 88
Abstracting datatypes 89
Universal quantification 89
Existential quantification and abstract datatypes 90
Phantom types 91
Generalized algebraic datatypes 94
Typecase pattern 95
Dynamic types 96
Heterogeneous lists 98
Abstracting type-classes 99
Multiparameter type-classes 99
Functional dependencies 100
Summary 101
Chapter 6: Patterns of Generic Programming 103
Patterns of generic programming 104
Patterns 1 and 2 – functions 104
Pattern 3 – polymorphic types and functions 104
Pattern 4 – type-class polymorphism 104
Pattern 5 – meta-programming 105
The Derivable type-classes 105
Generalized newtype deriving 105
Pattern 6 – type laws 105
Pattern 7 – datatype generic programming 106
The sum of products style 107
The sum of products type representation 108
Translating between the type and representation 109
Writing a datatype-generic function 109
Adding a new datatype 112
GHC.Generics – a generic deriving mechanism 112
Origami programming 113
Tying the recursive knot 113
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The generic map 114
The generic fold 115
main = print $ gfold addL aListF 116
Generic unfold and fold 116
Origami design patterns 117
Scrap your boilerplate 118
The type-safe cast with typeable 119
Type-safe function application 120
The shallow traversal and the data type-class 121
Typeable and data 123
Scrap your boilerplate 123
Summary 124
Chapter 7: Patterns of Kind Abstraction 125
Higher-order kinds 126
Higher-kinded polymorphism 127
Associated type synonyms 128
Using functional dependencies 128
Associated type synonyms 129
Associated types versus functional dependencies 130
Type (synonym) families 130
Data families 132
Kind polymorphism 132
The PolyKinds language extension 134
Type promotion 135
Promoting types to kinds 137
Type-level programming 138
Promoting term-level programs to type-level 139
Closed type families 139
The history of type-level programming in Haskell 140
Type-level and generic programming 140
Dependently-typed programming 141
Haskell and dependently-typed programming 142
Summary 143
Epilogue 143
Index 145