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Source for wiki GeneralizedEqualCowan version 3

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cowan

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70.44.231.3

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GeneralizedEqualCowan

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== Generalized `equal?` predicate ==

`(generalized-equal? `''obj1 obj2 comparator'' ... `)`

Compares ''obj1'' and ''obj2'' for equality. A ''comparator'' is a procedure that is given two arguments to compare. It returns `#t` if its arguments are to be considered equal, `#f` if they are to be considered unequal, and any other value if it cannot decide. A third argument consists of a list of comparators to be used in recursive calls to `generalize-equal?`.

First, each ''comparator'' argument is invoked on ''obj1'' and ''obj2''. If it returns `#t` or `#f`, that is the result. If all comparators have been invoked without a `#t` or `#f` result, then `generalized-equal?` determines if both ''obj1'' and ''obj2'' are ordered containers of the same type. This determination is partly implementation-dependent, but pairs, strings, vectors, and bytevectors must be treated as ordered containers of distinct types. If they are not, then `generalized-equal?` returns what `eqv?` returns on ''obj1'' and ''obj2''.

Otherwise, if the containers have different numbers of elements, the result is `#f`. Otherwise, `generalized-equal?` invokes itself recursively on each corresponding element of the containers, passing itself the same comparators. If a recursive call returns `#f`, that is the result; if all recursive calls return `#t`, that is the result.

== Sample comparators ==

These comparators may or may not be part of this package.

`(numeric-comparator `''obj1 obj2 comparators-list''`)`

A comparator that returns `#t` if ''obj1'' and ''obj2'' are numbers that are equal by `=`, `#f` if they are not equal by `=`, and a third value otherwise. The ''comparators-list'' argument is ignored.

`(char-ci-comparator `''obj1'' ''obj2 comparators-list''`)`

A comparator that returns `#t` if ''obj1'' and ''obj2'' are both characters that are equal by `char-ci=?`, `#f` if they are not equal by `char-ci=?`, and a third value otherwise.` The ''comparators-list'' argument is ignored.

`(string-ci-comparator `''obj1' obj2 comparators-list''`)`

A comparator that returns `#t` if ''obj1'' and ''obj2'' are both strings that are equal by `string-ci=?`, `#f` if they are not equal by `string-ci=?`, and a third value otherwise. The ''comparators-list'' argument is ignored.

`(hash-table-comparator `''obj1 obj2 comparators-list''`)`

A comparator that returns `#t` if ''obj1'' and ''obj2'' are both hash tables using the same comparison key, contain the same keys (in the sense of that comparison key), and map each key to the same value (in the sense of `generalized-equal?`, using the comparators in ''comparators-list''); returns `#f` if ''obj1'' and ''obj2'' are both hash tables but are distinct in the above sense; and returns a third value in all other cases.

time

2012-12-02 05:59:41