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Source for wiki EnumContainersCowan version 2

author

cowan

comment

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-ref` (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.

Possibly kill enum values in favor of just using enum maps?  A single value is very handy for C definitions, etc.

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

== Enumeration sets ==

From SetsCowan, not yet consistent with the above.

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.

This design is founded on [http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-15.html R6RS enumerations], but with the addition of reified enumeration types along the lines suggested by [http://www.r6rs.org/formal-comments/comment-262.txt R6RS Formal Comment #262].  The prefix `enum` is used in all cases instead of using both `enum` and `enumeration` as R6RS does.

`(enum-type-symbols `''enum-type''`)`

Return a newly allocated list of the symbols in ''enum-type'' in the original order.

`(enum-type-index `''enum-type symbol''`)`

Return an exact integer corresponding to the position of ''symbol'' in the original list that created ''enum-type'', or `#f` if it was not one of those symbols.  The R6RS equivalent is the procedure returned by `enum-type-indexer` when applied to an enum-set belonging to `enum-type`.

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

Returns a newly allocated enumeration set.  The possible elements of the set are the symbols in ''enum-type''.  The set is empty.  The approximate R6RS equivalents are `enum-set-constructor` and `make-enumeration`.

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

Returns a newly allocated enumeration set.  The possible elements of the set are the symbols 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 symbols belonging to ''enum-set'', ignoring any symbols which are not in ''enum-type''.  This procedure is also in R6RS, but uses a second enum-set in place of ''enum-type''.

== Enumeration maps ==

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

time

2014-08-04 10:08:54

version

2