# Bottom

The term **bottom** refers to a computation which never completes successfully. That includes a computation that fails due to some kind of error, and a computation that just goes into an infinite loop (without returning any data).

The mathematical symbol for bottom is '⊥'. That's Unicode character 22A5 hex = 8869 decimal. Also available in HTML as '⊥' and in LaTeX as '\bot' (within math mode). In plain ASCII, it's often written as the extremely ugly character sequence '`_|_`

'.

Bottom is a member of any type, even the trivial type () or the equivalent simple type:

```
data Unary = Unary
```

If it were not, the compiler could solve the halting problem and statically determine whether any computation terminated.

Bottom can be expressed in Haskell thus:

```
bottom = bottom
```

or

```
bottom = error "Non-terminating computation!"
```

Indeed, the Prelude exports a function

```
undefined = error "Prelude; undefined"
```