Go Lift - Speaker Deck

Slide 1

Slide 1 text

GO LIFT John Cinnamond dotGo 2017

Slide 2

Slide 2 text

PART 1 Constant interruptions

Slide 3

Slide 3 text

Connect to the server

Slide 4

Slide 4 text

Connect to the server Send ﬁrst command

Slide 5

Slide 5 text

Connect to the server Send ﬁrst command Wait for ok

Slide 6

Slide 6 text

Connect to the server Send ﬁrst command Wait for ok Send second command

Slide 7

Slide 7 text

conn := net.Dial(”tcp”, ”server:9876”)

Slide 8

Slide 8 text

No content

Slide 9

Slide 9 text

What if this goes wrong?

Slide 10

Slide 10 text

conn, err := net.Dial(”tcp”, ”server:9876”)

Slide 11

Slide 11 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) }

Slide 12

Slide 12 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) } conn.Write(command1)

Slide 13

Slide 13 text

No content

Slide 14

Slide 14 text

What if this goes wrong?

Slide 15

Slide 15 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) } , err := conn.Write(command1)

Slide 16

Slide 16 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) } , err := conn.Write(command1) if err != nil { panic(err) }

Slide 17

Slide 17 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) } , err := conn.Write(command1) if err != nil { panic(err) } r := buﬁo.NewReader(conn) status := r.ReadString(’\n’)

Slide 18

Slide 18 text

No content

Slide 19

Slide 19 text

. . . collaborate and listen

Slide 20

Slide 20 text

Slide 21

Slide 21 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) } , err := conn.Write(command1) if err != nil { panic(err) } r := buﬁo.NewReader(conn) status, err := r.ReadString(’\n’) if err != nil { panic(err) }

Slide 22

Slide 22 text

Slide 23

Slide 23 text

No content

Slide 24

Slide 24 text

. . . Hammer time

Slide 25

Slide 25 text

Slide 26

Slide 26 text

Handling errors is a good thing

Slide 27

Slide 27 text

Errors shouldn’t get in the way

Slide 28

Slide 28 text

conn := net.Dial(”tcp”, ”server:9876”) conn.Write(command1) r := buﬁo.NewReader(conn) status := r.ReadString(’\n’) if status == ”ok” { conn.Write(command2) }

Slide 29

Slide 29 text

conn := net.Dial(”tcp”, ”server:9876”) conn.Write(command1) r := buﬁo.NewReader(conn) status := r.ReadString(’\n’) if status == ”ok” { conn.Write(command2) } if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil if err != nil

Slide 30

Slide 30 text

Just use Haskell

Slide 31

Slide 31 text

PART 2 if err != nil

Slide 32

Slide 32 text

No content

Slide 33

Slide 33 text

Errors are values http://blog.golang.org/errors-are-values

Slide 34

Slide 34 text

conn.Write(command1)

Slide 35

Slide 35 text

conn.Write(command1) Not really the network

Slide 36

Slide 36 text

conn.Write(command1) Not really the network An abstraction

Slide 37

Slide 37 text

conn.Write(command1) Not really the network An abstraction A value

Slide 38

Slide 38 text

conn.Write(command1) Not really the network An abstraction A value . . . containing data about the connection

Slide 39

Slide 39 text

conn.Write(command1) Not really the network An abstraction A value . . . containing data about the connection . . . and behaviour to use it

Slide 40

Slide 40 text

A value . . . containing data about the connection . . . and behaviour to use it Determined by the type

Slide 41

Slide 41 text

Let’s add to the behaviour of net.Conn to handle errors

Slide 42

Slide 42 text

Let’s add to the behaviour of net.Conn to handle errors ⇒ create a new type

Slide 43

Slide 43 text

type SafeConn struct { }

Slide 44

Slide 44 text

type SafeConn struct { conn net.Conn }

Slide 45

Slide 45 text

type SafeConn struct { conn net.Conn err error }

Slide 46

Slide 46 text

func (c ∗SafeConn) write(b []byte) { }

Slide 47

Slide 47 text

func (c ∗SafeConn) write(b []byte) { c.conn.Write(b) }

Slide 48

Slide 48 text

Add error handling

Slide 49

Slide 49 text

func (c ∗SafeConn) write(b []byte) { c.conn.Write(b) }

Slide 50

Slide 50 text

func (c ∗SafeConn) write(b []byte) { , c.err := c.conn.Write(b) }

Slide 51

Slide 51 text

func (c ∗SafeConn) write(b []byte) { if c.err != nil { return } , c.err := c.Write(b) }

Slide 52

Slide 52 text

c := SafeConn{conn, nil}

Slide 53

Slide 53 text

c := SafeConn{conn, nil} c.write(command1) c.write(command2)

Slide 54

Slide 54 text

c := SafeConn{conn, nil} c.write(command1) // if this has an error c.write(command2)

Slide 55

Slide 55 text

c := SafeConn{conn, nil} c.write(command1) // if this has an error c.write(command2) // then this does nothing

Slide 56

Slide 56 text

c := SafeConn{conn, nil} c.write(command1) // if this has an error c.write(command2) // then this does nothing if c.err != nil { panic(”omg”) }

Slide 57

Slide 57 text

Repeat for other errors

Slide 58

Slide 58 text

conn, err := net.Dial(”tcp”, ”server:9876”) if err != nil { panic(err) }

Slide 59

Slide 59 text

func safeDial(network, address string) SafeConn { }

Slide 60

Slide 60 text

func safeDial(network, address string) SafeConn { conn, err := net.Dial(network, address) }

Slide 61

Slide 61 text

func safeDial(network, address string) SafeConn { conn, err := net.Dial(network, address) return SafeConn{conn, err} }

Slide 62

Slide 62 text

c := safeDial(”tcp”, ”server:9876”)

Slide 63

Slide 63 text

c := safeDial(”tcp”, ”server:9876”) c.write(command1) c.write(command2)

Slide 64

Slide 64 text

c := safeDial(”tcp”, ”server:9876”) c.write(command1) c.write(command2) if err != nil { panic(”never”) }

Slide 65

Slide 65 text

c := safeDial(”tcp”, ”server:9876”) // if this fails c.write(command1) c.write(command2) if err != nil { panic(”gonna”) }

Slide 66

Slide 66 text

c := safeDial(”tcp”, ”server:9876”) // if this fails c.write(command1) // then this does nothing c.write(command2) if err != nil { panic(”give”) }

Slide 67

Slide 67 text

c := safeDial(”tcp”, ”server:9876”) // if this fails c.write(command1) // then this does nothing c.write(command2) // same for this if err != nil { panic(”you”) }

Slide 68

Slide 68 text

We still handle the error

Slide 69

Slide 69 text

. . . but the error handling doesn’t get in the way

Slide 70

Slide 70 text

c := safeDial(”tcp”, ”server:9876”) c.write(command1) c.write(command2) if err != nil { panic(”up”) }

Slide 71

Slide 71 text

But wait!

Slide 72

Slide 72 text

We introduced a new abstraction

Slide 73

Slide 73 text

Abstractions have costs

Slide 74

Slide 74 text

c := safeDial(”tcp”, ”server:9876”) c.write(command1) // what happens if this fails c.write(command2) if err != nil { panic(err) }

Slide 75

Slide 75 text

Some details are hidden

Slide 76

Slide 76 text

. . . but this is nothing new

Slide 77

Slide 77 text

We use abstractions all the time

Slide 78

Slide 78 text

Is this abstraction appropriate?

Slide 79

Slide 79 text

PART 3 Division

Slide 80

Slide 80 text

Given 3 numbers (a, b, c) ⇒ a/b/c

Slide 81

Slide 81 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) }

Slide 82

Slide 82 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) } ... divide(100, 10, 2) // 5

Slide 83

Slide 83 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) } ... divide(100, 10, 0)

Slide 84

Slide 84 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) } ... divide(100, 10, 0) // panic: runtime error: integer divide by zero

Slide 85

Slide 85 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) } ... divide(100, 10, 0) // Can’t divide by zero

Slide 86

Slide 86 text

Let’s solve this badly

Slide 87

Slide 87 text

func divide(a, b, c int ) { if b == 0 || c == 0 { fmt. Printf (”Can’t divide by zero”) return } answer = a / b / c fmt. Println (answer) }

Slide 88

Slide 88 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) }

Slide 89

Slide 89 text

func divide(a, b, c int ) { answer := a / b / c fmt. Println (answer) } if b == 0 if b == 0 return if c == 0 if c == 0 if b == 0 if c == 0 if b == 0 if b == 0 if c == 0 if c == 0 if b == 0 return return

Slide 90

Slide 90 text

Is this like err != nil ?

Slide 91

Slide 91 text

Create a new type

Slide 92

Slide 92 text

Create a new type Wrap the initial value

Slide 93

Slide 93 text

Create a new type Wrap the initial value Wrap the behaviour

Slide 94

Slide 94 text

Create a new type Wrap the initial value Wrap the behaviour Wrap the conditionals

Slide 95

Slide 95 text

Create a new type

Slide 96

Slide 96 text

type Divideinator struct { answer int }

Slide 97

Slide 97 text

Wrap the initial value

Slide 98

Slide 98 text

d := Divideinator{a}

Slide 99

Slide 99 text

Wrap the behaviour

Slide 100

Slide 100 text

func (d ∗Divideinator) divide(x int ) { d.answer = d.answer / x }

Slide 101

Slide 101 text

Wrap the conditional

Slide 102

Slide 102 text

func (d ∗Divideinator) divide(x int ) { if x == 0 { d.isZero = true return } d.answer = d.answer / x }

Slide 103

Slide 103 text

func (d Divideinator) String () string { if d.isZero { return fmt. Sprintf (”Can’t divide by zero”) } return fmt. Sprintf (”%d”, d.answer) }

Slide 104

Slide 104 text

Put it all together

Slide 105

Slide 105 text

func divide(a, b, c int ) { d := Divideinator{a} }

Slide 106

Slide 106 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) }

Slide 107

Slide 107 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) d.divide(c) }

Slide 108

Slide 108 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) d.divide(c) fmt. Println (d) }

Slide 109

Slide 109 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) d.divide(c) fmt. Println (d) } ... divide(100, 10, 2) // 5

Slide 110

Slide 110 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) d.divide(c) fmt. Println (d) } ... divide(100, 0, 2) // Can’t divide by zero

Slide 111

Slide 111 text

func divide(a, b, c int ) { d := Divideinator{a} d.divide(b) d.divide(c) fmt. Println (d) } ... divide(100, 10, 0) // Can’t divide by zero

Slide 112

Slide 112 text

This is the same approach as error handling

Slide 113

Slide 113 text

Create a new type

Slide 114

Slide 114 text

Create a new type Wrap the initial value

Slide 115

Slide 115 text

Create a new type Wrap the initial value Wrap the behaviour

Slide 116

Slide 116 text

Create a new type Wrap the initial value Wrap the behaviour Wrap the conditional

Slide 117

Slide 117 text

I want to really understand this

Slide 118

Slide 118 text

Let’s look at the shape of the code

Slide 119

Slide 119 text

D(100) D(10) D(5) 100 10 5 divide(10) divide(2) /10 /2

Slide 120

Slide 120 text

D(100) D(10) D(5) 100 10 5 divide(10) divide(2) /10 /10 ; /2 /2

Slide 121

Slide 121 text

D(100) D(10) D(5) 100 10 5 divide(x) ; divide(y) divide(10) divide(2) /10 /0 /2 /0

Slide 122

Slide 122 text

Lift the initial value into a new type

Slide 123

Slide 123 text

D(100) D(10) D(5) 100 10 5 divide(x) ; divide(y) divide(10) divide(2) /10 /0 Divideinator /2 /0

Slide 124

Slide 124 text

Lift the behaviour

Slide 125

Slide 125 text

D(100) D(10) D(5) 100 10 5 divide(x) ; divide(y) divide(10) divide(2) /10 /0 Divideinator /2 /0

Slide 126

Slide 126 text

D(100) D(10) D(5) 100 10 5 divide(x) ; divide(y) divide(10) divide(2) /10 /0 Divideinator /2 /0

Slide 127

Slide 127 text

Lift the conditionals

Slide 128

Slide 128 text

D(100) D( ) D( ) 100 10 5 divide(x) ; divide(y) divide(0) divide(0) /10 /0 Divideinator /2 /0

Slide 129

Slide 129 text

D(100) D D 100 10 5 divide(x) ; divide(y) divide(x) divide(y) /10 /0 /2 /0

Slide 130

Slide 130 text

D(100) D D 100 10 5 divide(x) ; divide(y) divide(x) divide(y) /10 /0 /2 /0

Slide 131

Slide 131 text

SafeConn SafeConn SafeConn conn conn conn write() ; write() Write error Write error

Slide 132

Slide 132 text

SafeConn SafeConn SafeConn conn conn conn write() ; write() Write error Write error

Slide 133

Slide 133 text

SafeConn SafeConn SafeConn conn conn conn write() ; write() Write error Write error

Slide 134

Slide 134 text

SafeConn SafeConn SafeConn conn conn conn write() ; write() Write error Write error

Slide 135

Slide 135 text

SafeConn SafeConn SafeConn conn conn conn write() ; write()

Slide 136

Slide 136 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f g

Slide 137

Slide 137 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f g

Slide 138

Slide 138 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f T g

Slide 139

Slide 139 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f T g

Slide 140

Slide 140 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f T g T

Slide 141

Slide 141 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f T g T T

Slide 142

Slide 142 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f T g T T T

Slide 143

Slide 143 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f g

Slide 144

Slide 144 text

Ta Tb Tc a b c Tf Tf() ; Tg() Tg f g

Slide 145

Slide 145 text

Less math. More code.

Slide 146

Slide 146 text

PART 4 Building a webapp

Slide 147

Slide 147 text

http://doesgohavegenericsyet.com

Slide 148

Slide 148 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) validateEmail(email) }

Slide 149

Slide 149 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) validateEmail(email) checkAlreadyRegistered(email) }

Slide 150

Slide 150 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) validateEmail(email) checkAlreadyRegistered(email) register (email) }

Slide 151

Slide 151 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) validateEmail(email) checkAlreadyRegistered(email) register (email) sellEmailToRecruiters(email) }

Slide 152

Slide 152 text

Slide 153

Slide 153 text

Slide 154

Slide 154 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) if !validateEmail(email) { http .Error(w, ...) return } checkAlreadyRegistered(email) register (email) sellEmailToRecruiters(email) logRequest(r) fmt. Fprintln (w, ...) }

Slide 155

Slide 155 text

Slide 156

Slide 156 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) if !validateEmail(email) { logRequest(”invalid email”, r) http .Error(w, ...) return } if alreadyRegistered(email) { logRequest(”already registered”, r) http .Error(w, ...) return } register (email) sellEmailToRecruiters(email) logRequest(r) fmt. Fprintln (w, ...) }

Slide 157

Slide 157 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) if !validateEmail(email) { logRequest(”invalid email”, r) http .Error(w, ...) return } if alreadyRegistered(email) { sellEmailToRecruiters(email) logRequest(”already registered”, r) http .Error(w, ...) return } register (email) sellEmailToRecruiters(email) logRequest(r) fmt. Fprintln (w, ...) }

Slide 158

Slide 158 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) if !validateEmail(email) { logRequest(”invalid email”, r) http .Error(w, ...) return } if alreadyRegistered(email) { sellEmailToRecruiters(email) logRequest(”already registered”, r) http .Error(w, ...) return } if err := register (email); err != nil { sellEmailToRecruiters(email) logRequest(”registration failed ”, r) http .Error(w, ...) return }

Slide 159

Slide 159 text

Slide 160

Slide 160 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { email := r.FormValue(”email”) validateEmail(email) checkAlreadyRegistered(email) register (email) sellEmailToRecruiters(email) logRequest(r) fmt. Fprintln (w, ...) } if err != nil if alreadyRegistered logRequest if err != nil if !validateEmail logRequest if alreadyRegistered if err != nil sellEmail logRequest

Slide 161

Slide 161 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f g h i

Slide 162

Slide 162 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f g h i

Slide 163

Slide 163 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f g h i

Slide 164

Slide 164 text

We know how to do this

Slide 165

Slide 165 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f T g h i

Slide 166

Slide 166 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f T T g T h T i T

Slide 167

Slide 167 text

Ta Tb Tc Td Te a b c d e λ Tf Tf() ; Tg() ; Th() ; Ti() Tg Th Ti f T T g T h T i T T T T T

Slide 168

Slide 168 text

Create a new type Lift initial data Lift behaviour Lift control ﬂow

Slide 169

Slide 169 text

Create a new type

Slide 170

Slide 170 text

type SignupRequest struct { }

Slide 171

Slide 171 text

Lift initial data

Slide 172

Slide 172 text

type SignupRequest struct { w http .ResponseWriter r ∗http.Request }

Slide 173

Slide 173 text

Lift behaviour

Slide 174

Slide 174 text

func (s ∗SignupRequest) validate() { if s.email == ”” || ... { s.err = ” invalid email” } }

Slide 175

Slide 175 text

func (s ∗SignupRequest) checkNewRegistration() { if existingEmails.Contain(s.email) { s.err = ”already registered” } }

Slide 176

Slide 176 text

Lift control ﬂow

Slide 177

Slide 177 text

func (s ∗SignupRequest) checkNewRegistration() { if existingEmails.Contain(s.email) { s.err = ”already registered” } }

Slide 178

Slide 178 text

func (s ∗SignupRequest) checkNewRegistration() { if s.err != nil { return } if existingEmails.Contain(s.email) { s.err = ”already registered” } }

Slide 179

Slide 179 text

Compose the functions

Slide 180

Slide 180 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) }

Slide 181

Slide 181 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () }

Slide 182

Slide 182 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () s.checkNewRegistration() }

Slide 183

Slide 183 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () s.checkNewRegistration() s. register () }

Slide 184

Slide 184 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () s.checkNewRegistration() s. register () s.sellEmailToRecruiter() }

Slide 185

Slide 185 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () s.checkNewRegistration() s. register () s.sellEmailToRecruiter() s.log() }

Slide 186

Slide 186 text

func signupHandler(w http.ResponseWriter, r ∗http.Request) { s := newSignupRequest(w, r) s.validate () s.checkNewRegistration() s. register () s.sellEmailToRecruiter() s.log() s.respond() }

Slide 187

Slide 187 text

Please don’t write your request handlers like this

Slide 188

Slide 188 text

I’m not trying to tell you how to write code

Slide 189

Slide 189 text

I’m trying to give you something new to think about

Slide 190

Slide 190 text

Think about the shape of the code

Slide 191

Slide 191 text

Think about using types

Slide 192

Slide 192 text

I want to give you new tools

Slide 193

Slide 193 text

. . . to cope with complex code

Slide 194

Slide 194 text

It’s up to you to decide how to use them

Slide 195

Slide 195 text

Epilogue

Slide 196

Slide 196 text

We solve problems by breaking them into smaller pieces

Slide 197

Slide 197 text

. . . but then we need to join the pieces back together again

Slide 198

Slide 198 text

We need to understand the forces at play

Slide 199

Slide 199 text

Mathematics gives us this understanding

Slide 200

Slide 200 text

Mathematics lets us achieve more

Slide 201

Slide 201 text

Mathematics is pretty useful

Slide 202

Slide 202 text

Thank you John Cinnamond dotGo 2017 Gophers adapted from The Go Gopher by Renee French https://blog.golang.org/gopher