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sugar/coerce.rkt

165 lines
5.3 KiB
Racket

#lang racket/base
(require (for-syntax racket/base racket/syntax))
(require net/url racket/set racket/sequence "len.rkt" "define.rkt")
(define-syntax-rule (make-coercion-error-handler target-format x)
(λ(e) (error (string->symbol (format "->~a" target-format)) (format "Can't convert ~s to ~a" x target-format))))
(define+provide+safe (->int x)
(any/c . -> . integer?)
(with-handlers ([exn:fail? (make-coercion-error-handler 'int x)])
(cond
[(or (integer? x) (real? x)) (inexact->exact (floor x))]
[(complex? x) (->int (real-part x))]
[(string? x) (let ([strnum (string->number x)])
(if (real? strnum) (->int strnum) (error 'ineligible-string)))]
[(or (symbol? x) (path? x)) (->int (->string x))]
[(char? x) (char->integer x)]
[else (len x)]))) ; covers Lengthable types
(define+provide+safe (->string x)
(any/c . -> . string?)
(if (string? x)
x ; fast exit for strings
(with-handlers ([exn:fail? (make-coercion-error-handler 'string x)])
(cond
[(or (equal? '() x) (void? x)) ""]
[(symbol? x) (symbol->string x)]
[(number? x) (number->string x)]
[(path? x) (path->string x)]
[(char? x) (format "~a" x)]
[(url? x) (url->string x)]
[else (error 'bad-type)]))))
;; ->symbol, ->path, and ->url are just variants on ->string
;; two advantages: return correct type, and more accurate error
;; no need for "Symbolable" type - same as Stringable
(define+provide+safe (->symbol x)
(any/c . -> . symbol?)
(if (symbol? x)
x
(with-handlers ([exn:fail? (make-coercion-error-handler 'symbol x)])
(string->symbol (->string x)))))
(define+provide+safe (->path x)
(any/c . -> . path?)
(if (path? x)
x
(with-handlers ([exn:fail? (make-coercion-error-handler 'path x)])
(cond
[(url? x) (apply build-path (map path/param-path (url-path x)))]
[else (string->path (->string x))]))))
(define+provide+safe (->url x)
(any/c . -> . url?)
(with-handlers ([exn:fail? (make-coercion-error-handler 'url x)])
(string->url (->string x))))
(define+provide+safe (->complete-path x)
(any/c . -> . complete-path?)
(with-handlers ([exn:fail? (make-coercion-error-handler 'complete-path x)])
(path->complete-path (->path x))))
(define+provide+safe (->list x)
(any/c . -> . list?)
(if (list? x)
x
(with-handlers ([exn:fail? (make-coercion-error-handler 'list x)])
(cond
[(string? x) (list x)]
[(vector? x) (for/list ([i (in-vector x)])
i)]
[(set? x) (set->list x)]
;; conditional sequencing relevant because hash also tests true for `sequence?`
[(hash? x) (hash->list x)]
[(integer? x) (list x)] ; because an integer tests #t for sequence?
[(sequence? x) (sequence->list x)]
;[(stream? x) (stream->list x)] ;; no support for streams in TR
[else (list x)]))))
(define+provide+safe (->vector x)
(any/c . -> . vector?)
(if (vector? x)
x
(with-handlers ([exn:fail? (make-coercion-error-handler 'vector x)])
(list->vector (->list x)))))
(define+provide+safe (->boolean x)
(any/c . -> . boolean?)
(and x #t))
;; coercion contracts & *ish predicates
;; only make sense in untyped code
;; thus they are here.
(define-syntax-rule (make-blame-handler try-proc expected-sym)
(λ(b)
(λ(x)
(with-handlers ([exn:fail? (λ(e)
(raise-blame-error
b x
'(expected: "~a" given: "~e")
expected-sym x))])
(try-proc x)))))
(provide+safe make-coercion-contract)
(define-syntax (make-coercion-contract stx)
(syntax-case stx ()
[(_ stem coerce-proc)
(with-syntax ([coerce/stem? (format-id stx "coerce/~a?" #'stem)]
[can-be-stem? (format-id stx "can-be-~a?" #'stem)])
#'(make-contract
#:name 'coerce/stem?
#:projection (make-blame-handler coerce-proc 'can-be-stem?)))]
[(_ stem)
(with-syntax ([->stem (format-id stx "->~a" #'stem)])
#'(make-coercion-contract stem ->stem))]))
(define-syntax (define+provide-coercion-contract stx)
(syntax-case stx ()
[(_ stem)
(with-syntax ([coerce/stem? (format-id stx "coerce/~a?" #'stem)])
#'(begin
(provide+safe coerce/stem?)
(define coerce/stem? (make-coercion-contract stem))))]))
(define+provide-coercion-contract int)
(define+provide-coercion-contract string)
(define+provide-coercion-contract symbol)
(define+provide-coercion-contract path)
(define+provide-coercion-contract boolean)
(define+provide-coercion-contract list)
(define-syntax (make-*ish-predicate stx)
(syntax-case stx ()
[(_ stem)
(with-syntax ([stemish? (format-id stx "~aish?" #'stem)]
[->stem (format-id stx "->~a" #'stem)])
#`(begin
(provide+safe stemish?)
(define (stemish? x)
(with-handlers ([exn:fail? (λ(e) #f)]) (and (->stem x) #t)))))]))
(make-*ish-predicate int)
(make-*ish-predicate string)
(make-*ish-predicate symbol)
(make-*ish-predicate url)
(make-*ish-predicate complete-path)
(make-*ish-predicate path)
(make-*ish-predicate list)
(make-*ish-predicate vector)