6.2.901.900
2 Typed Utilities
2.1 Comparison Predicate Generation
See also alexis/util/comparator for untyped Racket forms.
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| maybe-adapter | | = | | | | | | | | | #:adapter adapter-expr : adapter-args-type |
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This provides a convenient macro for generating comparison predicates based on a "comparator"
function. The provided comparator-expr must evaluate to a function which takes two values and
produces either 0, 1, or -1. These values correspond to both parameters
being equal, the first parameter being greater, or the second parameter being greater, respectively.
The predicate-args-type must also be explicitly provided, which describes the types of values
that are permitted to be passed to the predicates.
Using this function, a set of functions is generated using predicate-base-id as a base
identifer to determine the names of the resulting definitions. This macro produces six functions,
their names acquired by appending =?, >?, <?, <>?, >=?,
and <=? to predicate-base-id.
If adapter-expr is provided, then it must evaluate to a function that takes a single
parameter and returns a single value. If specified, values will be threaded through
adapter-expr before being passed to comparator-expr. This allows values to
be mapped to other values before being provided to the comparator for additional processing or
parsing. The adapter-args-type expression must specify a type that describes the values that
may be passed to the adapter function.
Examples: |
| > (struct num-str ([num : Real] [str : String])) | | | > (: num-str-compare (num-str num-str -> (U -1 0 1))) | | | > (define (num-str-compare a b) | | (if (= (num-str-num a) (num-str-num b)) | | (let ([a (num-str-str a)] | | [b (num-str-str b)]) | | (cond | | [(string>? a b) 1] | | [(string<? a b) -1] | | [else 0])) | | (let ([a (num-str-num a)] | | [b (num-str-num b)]) | | (cond | | [(> a b) 1] | | [(< a b) -1] | | [else 0])))) |
| | | /home/racket/build-pkgs/user/.racket/6.2.901.900/pkgs/alexis | -util/typed/alexis/util/comparator.rkt:33:15: Type Checker: | missing type for identifier; | consider adding a type annotation with `:' | identifier: compare | in: compare | | > (num-str=? '(123 . "abc") '(123 . "abc")) | eval:6:0: Type Checker: missing type for top-level | identifier; | either undefined or missing a type annotation | identifier: num-str=? | in: "abc" | | > (num-str<? '(200 . "aaa") '(100 . "aaa")) | eval:7:0: Type Checker: missing type for top-level | identifier; | either undefined or missing a type annotation | identifier: num-str<? | in: "aaa" |
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The typed/alexis/util/comparator module also exports
comparison-predicates-out from alexis/util/comparator, which is compatible
with Typed Racket.