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Source for wiki EnumContainersCowan version 1

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cowan

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127.11.51.1

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EnumContainersCowan

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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.'''

== 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.

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.

The procedure `enum-set-value` is just the identity function, so it is not provided.

`(make-enum-type `''symbol-list''`)`

Returns a newly allocated enumeration type suitable for constructing enumeration sets whose members are the symbols in ''symbol-list''. These symbols are said to be ''in the enumeration type''. In R6RS the function of this procedure is provided as part of `make-enumeration`.

`(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''.

time

2014-07-26 02:56:05