# Unicode-symbols

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(Warn about HLint problems) |

## Revision as of 18:36, 5 April 2010

## Contents |

## 1 Overview

An overview of the packages that provide Unicode symbols.

Naming: A package ** X-unicode-symbols** defines new symbols for functions and operators from the package

**.**

`X`All symbols are documented with their actual definition and information regarding their Unicode code point. They should be completely interchangeable with their definitions.

Alternatives for existing operators have the same fixity. New operators will have a suitable fixity defined.

#### 1.1 UnicodeSyntax

GHC offers the UnicodeSyntax language extension. If you decide to use Unicode in your Haskell source then this extension can greatly improve how it looks.

## 2 base-unicode-symbols

Extra symbols for the base package.

API docs: http://hackage.haskell.org/package/base-unicode-symbols

darcs get http://code.haskell.org/~roelvandijk/code/base-unicode-symbols

#### 2.1 Problematic symbols

Original | Symbol | Code point | Name |
---|---|---|---|

not | ¬ | U+AC | NOT SIGN |

The problem with this symbol is that you would like to use it as a unary prefix operator:

¬(¬x) ≡ x

Unfortunately this is not valid Haskell. The following is:

(¬)((¬)x) ≡ x

But you can hardly call that an improvement over the simple:

not (not x) ≡ x

#### 2.2 HLint problems

HLint does not know about the fixities of the operators defined in *-unicode-symbols packages, and when run on a module containing an expression like

a == b ∧ c == d

HLint will immediately abort saying "hlint: Ambiguous infix expression".

So if being able to run your code through HLint is important to you, think twice about using *-unicode-syntax packages.

====New symbol ideas==== (*please add your own*)

## 3 containers-unicode-symbols

Extra symbols for the containers package.

API docs: http://hackage.haskell.org/package/containers-unicode-symbols

darcs get http://code.haskell.org/~roelvandijk/code/containers-unicode-symbols

#### 3.1 Fixities

What should the fixities for the following symbols be?

Symbol | Code point | Name |
---|---|---|

∪ | U+222A | UNION |

∩ | U+2229 | INTERSECTION |

⊆ | U+2286 | SUBSET OF OR EQUAL TO |

⊇ | U+2287 | SUPERSET OF OR EQUAL TO |

⊈ | U+2288 | NEITHER A SUBSET OF NOR EQUAL TO |

⊉ | U+2289 | NEITHER A SUPERSET OF NOR EQUAL TO |

⊂ | U+2282 | SUBSET OF |

⊃ | U+2283 | SUPERSET OF |

⊄ | U+2284 | NOT A SUBSET OF |

⊅ | U+2285 | NOT A SUPERSET OF |

Intuitively there is a correspondence with numerical operators. Compare the following operators:

∪ | + |

⊃ | > |

⊄ | ≮ |

Likewise you would like similar associativities and precedence levels:

x + y + z < w == ((x + y) + z) < w x ∪ y ∪ w ⊂ z == ((x ∪ y) ∪ z) ⊂ w

====New symbol ideas==== (*please add your own*)

## 4 Input methods

These symbols are all very nice but how do you type them?

(*please add info for other editors*)

### 4.1 Emacs

**Direct**

Enter symbols directly: `C-x 8 RET`, then type either the character's name or its hexadecimal code point.

**Custom script**

darcs get http://code.haskell.org/~roelvandijk/code/emacs-unicode-symbols

In your .emacs file:

(load "~/elisp/emacs-unicode-symbols/haskell-symbols") (defun haskell-unicode () (local-set-key (kbd "C-M-u") 'replace-haskell-unicode)) (add-hook 'haskell-mode-hook 'haskell-unicode)

With above hook installed navigate the point to right after a normal symbol like **->** and press ** C-M-u** to transform it into a beautiful

**→**.

*Caveat*: The author is an absolute Lisp newbie. Patches to above script are more than welcome.

**Abbrev mode**

The Abbrev mode is not suitable since it only deals with *words*, not *operators*.

**Agda**

Use Agda's input method.