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This SRFI provides a few extra procedures and comparators to go with SRFI 128, Comparators. Implementers are urged to add them to their SRFI 128 libraries, for which reason they are not packaged as a separate library.
The original specification for comparators was SRFI 114. This was a large and complex SRFI with many procedures and comparators; its sample implementation had many bugs. I replaced it with SRFI 128, which is much simpler and cleaner. However, I now believe that SRFI 114 was cut back too far. In particular, there are no comparators (as opposed to comparator constructors) in SRFI 128. This SRFI provides the comparators of SRFI 114 that seem generally useful, so as to have them generally available without needing to define them locally.
The SRFI 114 procedures comparator-max and
comparator-min have also been restored because they
are equivalent to the max and min methods
of the Haskell typeclass Ord. Comparators are equivalent
to the three typeclasses Eq, Ord, and
Hashable, but the first and last typeclass do not
provide any additional methods not already available in SRFI 128
except inequality, which is normally not provided by Scheme
libraries. Equivalent procedures that accept a list have also been added.
(comparator-max comparator obj1 obj2 ...)
(comparator-min comparator obj1 obj2 ...)
(comparator-max-in-list comparator list)
(comparator-min-in-list comparator list)
These procedures are analogous to min and max respectively,
but may be applied to any orderable objects, not just to real numbers. They
apply the ordering procedure of comparator to the objects to find
and return a minimal (or maximal) object. The order in which the
values are compared is unspecified.
If two objects are equal in the sense of the comparator, either may be returned.
The -in-list versions accept a single list argument.
These comparators are useful for comparing standard Scheme types, and should be more efficient than default comparators.
default-comparator
A pre-created default comparator.
It should behave exactly like a comparator returned by SRFI 128
make-default-comparator.
The following pre-created comparators must provide both ordering predicates and
hash functions. They behave exactly like comparators returned from the
example calls on make-comparator shown in SRFI 128.
boolean-comparator
A comparator for booleans such that #f compares before #t.
real-comparator
A comparator for real numbers such that smaller numbers compare before larger numbers.
char-comparator
A comparator for characters using Unicode codepoint order.
char-ci-comparator
A comparator for characters using char-ci<?.
string-comparator
A comparator for strings using the implementation-specific
definition of string<?.
string-ci-comparator
A comparator for strings using the implementation-specific
definition of string-ci<?.
pair-comparator
Compares pairs as if by the application of make-pair-comparator
to pairs with default-comparator as the car
and cdr comparators.
list-comparator
Compares lists as if by the application of make-list-comparator to lists
with default-comparator as the element comparator.
vector-comparator
Compares vectors as if by the application of make-vector-comparator to vectors
with default-comparator as the element comparator.
The following comparators behave exactly like the comparators
returned by calls to make-eq-comparator,
make-eqv-comparator,
and make-equal-comparator respectively.
eq-comparator
eqv-comparator
equal-comparator
The sample implementation is found in a single file in the repository of this
SRFI named srfi/128/162-impl.scm. It should simply be included in
whichever SRFI 128 library is in use by the implementation. It is important
to include it after all other files. It is also of course necessary to
extend the library exports to include the four new procedures and
thirteen new comparators.
Alternatively, there is a full implementation of the (srfi 128)
library including all extensions from this SRFI. The supported
Schemes are Chicken 5 and Chibi.
The following files are part of the implementation:
srfi-128.scm - Chicken 5 library for SRFI 128 + 162srfi/128.sld - Chibi library for SRFI 128 + 162srfi/128/128-impl.scm - SRFI 128 implementationsrfi/128/162-impl.scm - SRFI 162 implementationsrfi/128/default.scm - A portable implementation of
default-comparator, which implementations should extendsrfi/128/r7rs-shim.scm - A shim for Chicken 5 providing
the necessary R7RS-small proceduressrfi/128/complex-shim.scm - A shim for implementations
that don't support complex numbersshared-tests.scm - Shared tests depending on the
Chicken and Chibi test librarieschicken-tests.scm - A Chicken 5 wrapper for testschibi-tests.scm - A Chibi wrapper for testsPermission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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