updates
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commit
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#lang scribble/manual
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@(require scribble/eval (for-label racket "../main.rkt" sugar))
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@(define my-eval (make-base-eval))
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@(my-eval `(require sugar))
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@title{Coercion}
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@defmodule[sugar/coerce]
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@section{Values}
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@defmodule[sugar/coerce/value]
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@defproc[
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(->int
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[v any/c])
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integer?]
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Convert @racket[_v] to an integer in the least surprising way possible, or raise an error if it can't be done
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Numbers are rounded down to the nearest integer.
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Stringlike values are converted to numbers and rounded down.
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Characters are directly converted to integers.
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Lists, vectors, and other multi-value datatypes return their length (using @racket[len]).
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@examples[#:eval my-eval
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(map ->int (list 3 3.5 -2.5 (+ 3 (/ 1 2))))
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(map ->int (list "3.5" '3.5 (string->path "3.5")))
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(->int (list 5 6 7))
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(->int (hash 'a 1 'b 2 'c 3))
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(->int #t)
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]
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@defproc[
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(->string
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[v any/c])
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string?]
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Return the most natural string representation of @racket[_v], or raise an error if none exists.
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@examples[#:eval my-eval
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(->string "string")
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(->string 'symbol)
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(->string 98.6)
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(->string (string->path "stdio.h"))
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(->string #\u0041)
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(->string #t)
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]
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@defproc[
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(->symbol
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[v any/c])
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symbol?]
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Same as @racket[->string], but returns a symbol rather than a string.
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@examples[#:eval my-eval
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(->symbol "string")
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(->symbol 'symbol)
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(->symbol 98.6)
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(->symbol (string->path "stdio.h"))
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(->symbol #\u0041)
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(->symbol #t)
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]
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@deftogether[(
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@defproc[
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(->path
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[v any/c])
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path?]
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@defproc[
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(->complete-path
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[v any/c])
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complete-path?]
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)]
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Same as @racket[->string], but returns a path (or complete path) rather than a string.
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@examples[#:eval my-eval
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(->path "string")
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(->path 'symbol)
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(->complete-path 98.6)
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(->complete-path (string->path "stdio.h"))
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(->complete-path #\u0041)
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(->complete-path #t)
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]
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@defproc[
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(->list
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[v any/c])
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list?]
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Convert a listlike @racket[_v] into a list, or put an atomic @racket[_v] into a single-member list.
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@examples[#:eval my-eval
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(->list "string")
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(->list 'symbol)
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(->list +)
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(->list '(a b c))
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(->list (list->vector '(a b c)))
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]
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@defproc[
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(->vector
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[v any/c])
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vector?]
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Same as @racket[->list], but returns a vector rather than a list.
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@examples[#:eval my-eval
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(->vector "string")
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(->vector 'symbol)
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(->vector +)
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(->vector '(a b c))
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(->vector (list->vector '(a b c)))
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]
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@defproc[
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(->boolean
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[v any/c])
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boolean?]
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Return @racket[#t] for any @racket[_v] except @racket[#f], which remains @racket[#f]. Same as @code{(and v #t)}.
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@examples[#:eval my-eval
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(map ->boolean (list "string" 'symbol + '(l i s t) #f))
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]
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@deftogether[(
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@defproc[(intish? [v any/c]) boolean?]
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@defproc[(stringish? [v any/c]) boolean?]
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@defproc[(symbolish? [v any/c]) boolean?]
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@defproc[(pathish? [v any/c]) boolean?]
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@defproc[(complete-pathish? [v any/c]) boolean?]
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)]
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Report whether @racket[_v] can be coerced to the specified type.
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@examples[#:eval my-eval
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(map intish? (list 3 3.5 #\A "A" + #t))
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(map stringish? (list 3 3.5 #\A "A" + #t))
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(map symbolish? (list 3 3.5 #\A "A" + #t))
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(map pathish? (list 3 3.5 #\A "A" + #t))
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(map complete-pathish? (list 3 3.5 #\A "A" + #t))
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]
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@section{Contracts}
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@defmodule[sugar/coerce/contract]
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@deftogether[(
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@defproc[(coerce/int? [v any/c]) int?]
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@defproc[(coerce/string? [v any/c]) string]
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@defproc[(coerce/symbol? [v any/c]) symbol]
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@defproc[(coerce/path? [v any/c]) path?]
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@defproc[(coerce/boolean? [v any/c]) boolean?]
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)]
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If @racket[_v] can be coerced to the specified type, these contracts will return it so coerced. If not, they raise the usual contract error. This is an unusual way to use contracts, but it can be handy.
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@examples[#:eval my-eval
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(define/contract (add-ints x y)
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(coerce/int? coerce/int? . -> . any/c)
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(+ x y))
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(add-ints 1.6 3.8)
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(define/contract (int-sum x y)
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(any/c any/c . -> . coerce/int?)
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(+ x y))
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(int-sum 1.6 3.8)
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]
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@defproc[
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(make-coercion-contract
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[type string?])
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contract?]
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Make a coercion contract named @code{coerce/type?} that will coerce a value to the speficied type. Assumes the existence of a @code{->type} function to do the coercion.
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@examples[#:eval my-eval
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(define (->list x)
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(if (list? x) x (list x)))
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(define coerce/list? (make-coercion-contract list))
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(define/contract (listify x)
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(any/c . -> . coerce/list?)
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x)
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(listify '(a b c))
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(listify 24)
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]
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