Talking To machines

Introduction

programming is not

black magic

You don't need to be able to...

read lines and lines of abstract symbols
simulate a computer in your head
understand abstract mathematics

...to be a programmer!

Logic is all you need

All you need to be able to do is think logically.

Logic is all you need

What do we mean by logic, exactly?

if a person is pregnant, then they are female

is not the same as

if a person is female, then they are pregnant

Luckily for everyone, as this would mean that

women are pregnant all the time

Logic is all you need

What do we mean by logic, exactly?

if a person is pregnant, then they are female

is the same as

there is no pregnant person that is not female

This means that men cannot get pregnant.

Which happens to be true!

True and false

How can we tell the difference between

things that are true and things that are false?

Simpler language

Simple language makes logic easier to follow

if a person is pregnant, then they are female

(pregnant p) => (female p)

if a person is female, then they are pregnant

(female p) => (pregnant p)

Being before or after the arrow

changes the meaning of the sentence!

Arrows

(pregnant p) => (female p)

If the thing to the left of the arrow is true,

the thing to the right of the arrow must be true

If you are pregnant then you must be female

Arrows

(pregnant p) => (female p)

If the thing to the right of the arrow is true,

the thing to the left of the arrow is not necessarily true

You can be female without being pregnant

Arrows

(pregnant p) => (female p)

(not (female p)) => (not (pregnant p))

If we want to swap the order of the things,

we need to need to negate them using not.

WHY?

If you are not female, then you cannot be pregnant. Because if you were pregnant, then you would be female!

Even simpler language

a => b

(not b) => (not a)

This rule is true for any a and b you can think of!

(monday today) => (tuesday tomorrow)

(not (tuesday tomorrow)) => (not (monday today))

Logical nonsense

a => b

(not b) => (not a)

What about these values for a and b?

(pregnant p) => (male p)

(not (male p)) => (not (pregnant p))

The conclusion is true given the premise. If our premises are false, then our conclusions might be too.

logic is not truth

A logical inference does not have to be

empirically true.

But if we start from truthful premises we

are guaranteed to end up with true conclusions!

programming machines

A programming language is nothing more

than an unambiguous notation for ideas

Computers are machines that carry out

logical operations

A program is a collection of definitions and

some logical inferences we can draw from them

Definitions of male, female and pregnancy.

Inferences about what gender can be pregnant.