Newton’s Laws of Motion

1. Inertia

2. Acceleration

3. Action-reaction

Force

Mass

Distance

Time

Aristotelian Physics(excerpt)

Ideal speed

Natural place

Natural motion

Unnatural motion

Why use Functional Programming?

What is Functional Programming?

A Theory of Functional

Programming

Eric Normand

LambdUp December 6, 2017

New Orleans February 15 & 16, 2018

clojuresync.com

10% off: LAMBDUP

paradigm

a philosophical and theoretical framework of a scientific school or discipline within which theories, laws, and generalizations and the experiments performed in support of them are formulated

Merriam-Webster

philosophical or theoretical framework,

world view

theories, laws, generalizations

basic assumptions, ways of thinking, methodology

Why use Functional Programming?

What is Functional Programming?

Goals of my Theory

Goals of my Theory• Explain what it is we (functional programmers) actually do

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

• Explain why it has advantages over other paradigms

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

• Explain why it has advantages over other paradigms

• to people who haven’t done FP

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

• Explain why it has advantages over other paradigms

• to people who haven’t done FP

• Avoid focusing on features

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

• Explain why it has advantages over other paradigms

• to people who haven’t done FP

• Avoid focusing on features

• Give explanatory and predictive power

Goals of my Theory• Explain what it is we (functional programmers) actually do

• in terms we can all understand

• Explain why it has advantages over other paradigms

• to people who haven’t done FP

• Avoid focusing on features

• Give explanatory and predictive power

• Self-described functional programmers should agree

My Theory of FP

My Theory of FP

Actions

My Theory of FP

Actions Data

My Theory of FP

Actions Data Calculations

Actions

Actionsthe process of doing something, typically to achieve an aim

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

• Depend on when you run them or how many times you run them

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

• Depend on when you run them or how many times you run them

• Examples

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

• Depend on when you run them or how many times you run them

• Examples

• Sending a message over the network

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

• Depend on when you run them or how many times you run them

• Examples

• Sending a message over the network

• Writing to file system — other programs can see the change

Actionsthe process of doing something, typically to achieve an aim

• Typically called Effects or Side-effects

• Depend on when you run them or how many times you run them

• Examples

• Sending a message over the network

• Writing to file system — other programs can see the change

• Changing or reading mutable state

Data

Datafactual information used as a basis for reasoning, discussion, or calculation

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

• Examples

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

• Examples

• Numbers

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

• Examples

• Numbers

• Bytes

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

• Examples

• Numbers

• Bytes

• Strings

Datafactual information used as a basis for reasoning, discussion, or calculation

• Inert

• Serializable

• Requiring interpretation

• Examples

• Numbers

• Bytes

• Strings

• Collections

Calculations

Calculationscomputation from inputs to outputs

Calculationscomputation from inputs to outputs

• Mathematical functions

Calculationscomputation from inputs to outputs

• Mathematical functions

• Eternal — outside of time

Calculationscomputation from inputs to outputs

• Mathematical functions

• Eternal — outside of time

• Referentially transparent

Calculationscomputation from inputs to outputs

• Mathematical functions

• Eternal — outside of time

• Referentially transparent

• Examples

Calculationscomputation from inputs to outputs

• Mathematical functions

• Eternal — outside of time

• Referentially transparent

• Examples

• List concatenation

Calculationscomputation from inputs to outputs

• Mathematical functions

• Eternal — outside of time

• Referentially transparent

• Examples

• List concatenation

• Summing numbers

Contrast with OOP

OOP

OOP

Objects

OOP

Objects References

OOP

Objects References Messages

ImplementationHaskell

• Data — built-in types and defined types

• Calculations — functions

• Actions — IO type

ImplementationClojure

• Data — built-in types

• Calculations — pure functions

• Actions — impure functions

Further down the rabbit hole

• Everything “First-class”

• Data

• Calculations

• Actions

• Minimum necessary to program functionally in a language

Domains are separate

Domains are separateData

Domains are separateData

Data + Data => Data

Domains are separateData

Data + Data => Data

Examples

Domains are separateData

Data + Data => Data

Examples

• Addition

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Actions

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Actions

Actn + Actn => Actn

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Actions

Actn + Actn => Actn

Examples

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Actions

Actn + Actn => Actn

Examples

• in sequence

Domains are separateData

Data + Data => Data

Examples

• Addition

• Concatenation

Calculations

Calc + Calc => Calc

Examples

• compose

• juxtapose

Actions

Actn + Actn => Actn

Examples

• in sequence

• in parallel

Actions

Actions• Contagious!

Actions• Contagious!

• Calculation + Action => Action

Actions• Contagious!

• Calculation + Action => Action

• Data + Action => Action

Actions• Contagious!

• Calculation + Action => Action

• Data + Action => Action

• Examples

Actions• Contagious!

• Calculation + Action => Action

• Data + Action => Action

• Examples

• Print the square of a number — square => print!

Actions• Contagious!

• Calculation + Action => Action

• Data + Action => Action

• Examples

• Print the square of a number — square => print!

• Parse the input as a number — read! => parse

Calculations

Calculations• Algebraic manipulation

Calculations• Algebraic manipulation

• Turing complete

Calculations• Algebraic manipulation

• Turing complete

• implies the Halting problem

Calculations• Algebraic manipulation

• Turing complete

• implies the Halting problem

• Opaque

Calculations• Algebraic manipulation

• Turing complete

• implies the Halting problem

• Opaque

• What is this code going to do?

Calculations• Algebraic manipulation

• Turing complete

• implies the Halting problem

• Opaque

• What is this code going to do?

• Only way to know is to run it

Data

• Can represent something else

• Structure

• Known Big-O complexities

RefactoringsActions

• Action => Action + Calculation

• Action => Action + Data

• Action => Action + Action

Calculations

• Calculation => Calculation + Data

• Calculation => Calculation + Calculation

Actions are universal

Actions

Calculations

Data

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

Pure function

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

Pure functiontakes 24 hours to compute

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

Pure functiontakes 24 hours to compute

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

Pure functiontakes 24 hours to compute

Read/write to temp file as buffer

What counts as an Action?

Calculations

Timeless

Actions

Bound in time

Pure function Read/write to disk

Pure functiontakes 24 hours to compute

Read/write to temp file as buffer

Actions how many times they run

Actions how many times they run

always matters - 0≠1≠more

Actions how many times they run

always matters - 0≠1≠morelaunching a missile

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

idempotent - 0≠1=more

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

idempotent - 0≠1=moresetting public flag to true

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

idempotent - 0≠1=moresetting public flag to true

free of side-effects - 0=1=more

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

idempotent - 0≠1=moresetting public flag to true

free of side-effects - 0=1=moreGET request

Actions how many times they run

always matters - 0≠1≠morelaunching a missilesending an email

idempotent - 0≠1=moresetting public flag to true

free of side-effects - 0=1=moreGET request

reading mutable state

Actions when they run

Actions when they run

transactional read

Actions when they run

transactional readguaranteed to be consistent

Actions when they run

transactional readguaranteed to be consistent

transactional+serialized writes

Actions when they run

transactional readguaranteed to be consistent

transactional+serialized writesOrder matters, but at least it’s some order

Actions when they run

transactional readguaranteed to be consistent

transactional+serialized writesOrder matters, but at least it’s some order

exactly once reads

Actions when they run

transactional readguaranteed to be consistent

transactional+serialized writesOrder matters, but at least it’s some order

exactly once readsCommunicating Sequential Processes