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GO LIFT John Cinnamond dotGo 2017

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PART 1 Constant interruptions

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Connect to the server

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Connect to the server Send first command

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Connect to the server Send first command Wait for ok

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

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

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No content

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What if this goes wrong?

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

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

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

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No content

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What if this goes wrong?

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

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

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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’)

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No content

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. . . collaborate and listen

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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’)

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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) }

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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) } if status == ”ok” { conn.Write(command2) }

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No content

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. . . Hammer time

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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) } if status == ”ok” { , err := conn.Write(command2) if err != nil { panic(err) } }

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Handling errors is a good thing

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Errors shouldn’t get in the way

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

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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

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Just use Haskell

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PART 2 if err != nil

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No content

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

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conn.Write(command1)

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conn.Write(command1) Not really the network

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

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

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

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

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

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

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

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type SafeConn struct { }

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type SafeConn struct { conn net.Conn }

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type SafeConn struct { conn net.Conn err error }

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

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

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Add error handling

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

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

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

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c := SafeConn{conn, nil}

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

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

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

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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”) }

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Repeat for other errors

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

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func safeDial(network, address string) SafeConn { }

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

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

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c := safeDial(”tcp”, ”server:9876”)

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

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

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

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

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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”) }

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We still handle the error

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

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

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But wait!

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We introduced a new abstraction

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Abstractions have costs

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

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Some details are hidden

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. . . but this is nothing new

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We use abstractions all the time

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Is this abstraction appropriate?

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PART 3 Division

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Given 3 numbers (a, b, c) ⇒ a/b/c

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

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

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

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

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

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Let’s solve this badly

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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) }

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

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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

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Is this like err != nil ?

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Create a new type

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Create a new type Wrap the initial value

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Create a new type Wrap the initial value Wrap the behaviour

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

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Create a new type

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type Divideinator struct { answer int }

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Wrap the initial value

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d := Divideinator{a}

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Wrap the behaviour

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

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Wrap the conditional

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

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

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Put it all together

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

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

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

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

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

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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

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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

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This is the same approach as error handling

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Create a new type

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Create a new type Wrap the initial value

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Create a new type Wrap the initial value Wrap the behaviour

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

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I want to really understand this

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Let’s look at the shape of the code

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

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

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

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Lift the initial value into a new type

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

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Lift the behaviour

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

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

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Lift the conditionals

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Less math. More code.

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PART 4 Building a webapp

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http://doesgohavegenericsyet.com

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

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

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

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

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

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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, ...) }

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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, ...) }

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

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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, ...) }

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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, ...) }

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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 }

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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, ...) }

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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

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

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

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

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We know how to do this

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

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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

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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

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

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Create a new type

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type SignupRequest struct { }

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Lift initial data

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

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Lift behaviour

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

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

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Lift control flow

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

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

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Compose the functions

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

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

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

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

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

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

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

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Please don’t write your request handlers like this

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

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

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Think about the shape of the code

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Think about using types

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I want to give you new tools

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. . . to cope with complex code

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

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Epilogue

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We solve problems by breaking them into smaller pieces

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

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We need to understand the forces at play

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Mathematics gives us this understanding

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Mathematics lets us achieve more

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Mathematics is pretty useful

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