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Source for wiki EnumContainersCowan version 4

author

cowan

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ipnr

127.11.51.1

name

EnumContainersCowan

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0

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'''THIS IS NOT A PROPOSAL.  It's just a dumping ground for some stuff I don't want to lose track of.  There will be a proper proposal later.'''

== Enumerations ==

Based on unique objects, not symbols.

Each enum object has four properties:  enum type, name (a symbol), ordinal (a non-negative exact integer), value (anything).  Enum objects are unique across enum types.  Names and ordinals are unique within an enum type.  Accessors are `enum-type`, `enum-name`, `enum-ordinal`, `enum-value`.

An enum type contains a map from names to enum objects and a vector indexed by the ordinal.  We need `enum-ordinal->enum` (uses the vector) and `enum-name->enum` (uses the map) as fundamental procedures on enum types.  Simple composition gives us `enum-name->ordinal`, `enum-ordinal->name`, `enum-ordinal->value`, and `enum->name->value`.  There is no way to work backward from an enum value because it need not be unique.  

Having a single value is very handy for C definitions, etc.

Operations over the whole enum-type: `enum-type-size`, `enum-type-enums` and `enum-type-names`.  Maybe `enum-type-values` as well.

`Make-enumeration-type` accepts either names or `(name value)` lists.  Ordinals are assigned in order from 0 upward; values default to same as ordinals.  `Define-enumeration-type` binds an identifier to the enumeration type and an identifier per enum (same as the name) to each enum.

== Enumeration sets ==

Except as noted below, the procedures for creating and manipulating enumeration sets are the same as those for sets, except that `set` is replaced by `enum-set` in their names.  Wherever a newly allocated enumeration set is returned, it has the same enumeration type as the source sets.  It is an error to operate on enumeration sets of different types in a single procedure.

`(universal-enum-set `''enum-type''`)`

Returns a newly allocated enumeration set.  The possible elements of the set are the enum objects in ''enum-type''.  The set contains all possible elements.  The approximate R6RS equivalent is `enum-set-universe`.

`(enum-set `''enum-type''` `''element'' ...`)`

Returns a newly allocated enumeration set.  The possible elements of the set are the symbols in ''enum-type''. The set is initialized to contain the ''elements''.  There is no R6RS equivalent.

`(list->enum-set `''enum-type''` `''list''`)`

Returns a newly allocated enumeration set.  The possible elements of the set are the symbols in ''enum-type''. The set is initialized to contain the elements of ''list''.  There is no R6RS equivalent.

`(enum-set-complement `''enum-set''`)`

Returns a newly allocated enumeration set that is the complement of ''enum-set''.  This procedure is also in R6RS.

`(enum-set-projection `''enum-set''` `''enum-type''`)`

Returns a newly allocated enumeration set of type ''enum-type''.  Its elements are the enum objects in ''enum-type'' which have the same names as members of ''enum-set''.  Enum objects without corresponding names are ignored.  This procedure is also in R6RS, but uses a second enum-set in place of ''enum-type''.

There will probably be more, depending on how integer sets turn out:  `enum-set-complement`, `enum-set-complement!`, `enum-set-min`, `enum-set-max`.

== Enumeration maps ==

Based on vectors indexed by the enum's ordinal.  API is a reduced form of HashTablesCowan.

time

2014-08-17 14:33:17

version

4