Difference between revisions of "Bottom"
Jump to navigation
Jump to search
(bold keyword) |
JaredUpdike (talk | contribs) (Added remark that _|_ is a member of any type) |
||
| Line 2: | Line 2: | ||
The mathematical symbol for bottom is '⊥'. That's Unicode character 22A5 hex = 8869 decimal. Also available in HTML as '&perp;' and in LaTeX as '\bot' (within math mode). In plain ASCII, it's often written as the extremely ugly character sequence '<code>_|_</code>'. |
The mathematical symbol for bottom is '⊥'. That's Unicode character 22A5 hex = 8869 decimal. Also available in HTML as '&perp;' and in LaTeX as '\bot' (within math mode). In plain ASCII, it's often written as the extremely ugly character sequence '<code>_|_</code>'. |
||
| + | |||
| + | Bottom is a member of any type, even the trivial type () or the equivalent simple type: |
||
| + | |||
| + | <haskell> |
||
| + | data Unary = Unary |
||
| + | </haskell> |
||
| + | |||
| + | If it were not, the compiler could solve the [http://en.wikipedia.org/wiki/Halting_problem halting problem] and statically determine whether any computation terminated. |
||
| + | |||
| + | Bottom can be expressed in Haskell thus: |
||
| + | |||
| + | <haskell> |
||
| + | bottom = bottom |
||
| + | </haskell> |
||
| + | |||
| + | or |
||
| + | |||
| + | <haskell> |
||
| + | bottom = error "Non-terminating computation!" |
||
| + | </haskell> |
||
[[Category:Glossary]] |
[[Category:Glossary]] |
||
Revision as of 21:37, 4 January 2008
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!"