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67 lines
2.1 KiB
Racket
67 lines
2.1 KiB
Racket
#lang racket/base
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(require "base.rkt"
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racket/class
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racket/match
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racket/contract)
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
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|#
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(define x:optional%
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(class x:base%
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(super-new)
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(init-field [(@type type)] [(@condition condition)])
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(unless (xenomorphic? @type)
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(raise-argument-error 'x:optional "xenomorphic type" @type))
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(define (resolve-condition parent)
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(match @condition
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[(? procedure? proc) (proc parent)]
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[val val]))
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(define/augment (x:decode port parent)
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(when (resolve-condition parent)
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(send @type x:decode port parent)))
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(define/augment (x:encode val port [parent #f])
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(when (resolve-condition parent)
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(send @type x:encode val port parent)))
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(define/augment (x:size [val #f] [parent #f])
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(if (resolve-condition parent) (send @type x:size val parent) 0))))
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(define no-val (gensym))
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(define (x:optional? x) (is-a? x x:optional%))
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(define/contract (x:optional
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[type-arg #f]
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[cond-arg no-val]
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#:type [type-kwarg #f]
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#:condition [cond-kwarg no-val]
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#:pre-encode [pre-proc #f]
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#:post-decode [post-proc #f]
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#:base-class [base-class x:optional%])
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(()
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((or/c xenomorphic? #false)
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any/c
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#:type (or/c xenomorphic? #false)
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#:condition any/c
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#:pre-encode (or/c (any/c . -> . any/c) #false)
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#:post-decode (or/c (any/c . -> . any/c) #false)
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#:base-class (λ (c) (subclass? c x:optional%)))
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. ->* .
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x:optional?)
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(define type (or type-arg type-kwarg))
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(unless (xenomorphic? type)
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(raise-argument-error 'x:optional "xenomorphic type" type))
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(define condition (cond
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[(and (eq? cond-arg no-val) (eq? cond-kwarg no-val)) #true]
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[(not (eq? cond-arg no-val)) cond-arg]
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[(not (eq? cond-kwarg no-val)) cond-kwarg]))
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(new (generate-subclass base-class pre-proc post-proc) [type type] [condition condition]))
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