Personal tools

User:Zzo38/Proposal for more-notation

From HaskellWiki

< User:Zzo38
Revision as of 20:47, 27 August 2011 by Zzo38 (Talk | contribs)

Jump to: navigation, search

This document is proposal for more-notation in Haskell.

Contents

1 Syntax

Anywhere that a more-notation is allowed (see Uses), you can use the syntax:

  • more [(name_of_enumeration)] more_name {parameters}
  • name_of_enumeration: A name of any type which is an enumeration. It can be another one using more-notation, but it must be able to fully determine it before this more-notation can be fully determined.
  • more_name: A capitalized name. It uses the same namespace as constructors, so you are not allowed to have a constructor of the same name (although it is OK to have types of the that name).
  • parameters: Optional lowercased names. These names are in local scope, and may already exist in this scope, although they do not have to.

A more-declaration is a module-level declaration of this syntax:

  • [ numeric_literal | (enumeration_constructor) ] more_name {parameters} = contents { | contents } ;
  • numeric_literal: It should be a natural number. Omitted is the same as zero.
  • enumeration_constructor: A constructor of the enumeration that was specified in the more-notation. If an enumeration is specified, the enumeration constructor is required here.
  • parameters: Lowercased names which will be scoped locally to this declaration. The number of parameters must match the number of parameters specified in the more-notation.
  • contents: The contents depends on where the more-notation is.

2 Semantics

In the place where the more-notation is, all contents of more-declarations of that name will be reordered and corrected before being placed in place of the more-notation.

Automatic reordering is overridden by the enumeration constructors or numeric literals in front of more-declarations.

3 Uses

3.1 Do-blocks

3.2 Case alternatives

3.3 Datatype declarations

A constructor definition in a data declaration is allowed to be replaced by a more-notation. Semantics of more-declarations becomes as follows:

  • Duplicate constructors are removed.
  • Duplicate constructors that do not match are errors.
  • Multiple constructors in a single more-declaration are guaranteed to keep the order given.

Example:

data T = Zero | more T deriving (Eq);
T = Two | Three | Four;
T = One | Two;

becomes

data T = Zero | One | Two | Three | Four deriving (Eq);

3.4 Fields in record syntax

3.5 Lists

4 Combining with Template Haskell

4.1 Uses in quotations

4.2 Manipulation in splices

4.3 Types and constructors