# Unicode-symbols

## 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.

#### 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

Original Symbol Code point Name

## 3 containers-unicode-symbols

Extra symbols for the containers package.

#### 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

## 4 Input methods

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

### 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

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.