Programs are a way for us humans to communicate with machines. Literals, symbols and bindings of symbols to values are incredibly fundamental, and yet often left implicit.

I finally understood that the half page of code on the bottom of page 13 of the Lisp 1.5 manual was Lisp in itself. These were Maxwell’s Equations of Software!

Alan Kay

## Literals

• We can specify data verbatim as part of the source code. The syntax that allows us to do this is called literals.

• String literal "Hello world"
• Numerical literal 3.14159265

## Symbols / Variables

• We can give data one or more names. The names we give to data is called a symbol which are also known as variables.

## Bindings

• Symbols are only useful when they label some data. When a symbol $\pi$ is used as a label of a value 3.14159265, we say that $\pi$ is bound to the value 3.14159265.