Today I decided to convert all structure definitions in a Typed Racket file
to lists. For instance,
(struct foo ([x : Integer]))
would become a tagged list:
(define-type foo (Pairof 'foo (List Integer)))
along with a constructor, predicate, and accessors.
Using a macro, I was able to write what I wanted to do once and use it for
multiple structures.
Here's how it looked in one file: all I had to do was write the macro, use
"struct2" instead of "struct", and remove uses of "struct-out". Other files
in the project worked with the new data definition, no problems.
#lang typed/racket
(require (for-syntax racket/base syntax/parse racket/syntax))
(define-syntax (struct2 stx)
(syntax-parse stx #:datum-literals (:)
[(_ name:id ([f*:id : t*] ...))
#:with ((name-f* i*) ...)
(for/list ([f (in-list (syntax-e #'(f* ...)))]
[i (in-naturals 1)])
(list (format-id stx "~a-~a" (syntax-e #'name) (syntax-e f)) i))
#:with Name (format-id stx "~a" (string-titlecase (symbol->string
(syntax-e #'name))))
#:with name? (format-id stx "~a?" (syntax-e #'name))
(syntax/loc stx (begin
(define-type Name (Pairof 'name (Listof Any)))
(provide Name)
(define (name (f* : t*) ...) : Name
(list 'name f* ...))
(provide name)
(define (name-f* (p : Name)) : t*
(cast (list-ref p 'i*) t*))
...
(provide name-f* ...)
(define (name? (v : Any)) : Boolean
(and (list? v) (not (null? v)) (eq? 'name (car v)))) ))]))
(struct2 posn ([x : Real]
[y : Real]))
(struct2 block ([x : Real]
[y : Real]
[color : Symbol]))
(struct2 tetra ([center : Posn]
[blocks : (Listof Block)]))
(struct2 world ([tetra : Tetra]
[blocks : (Listof Block)]))
(: posn=? (-> Posn Posn Boolean))
(define (posn=? p1 p2)
(and (= (posn-x p1) (posn-x p2))
(= (posn-y p1) (posn-y p2))))
(provide posn=?)
(Nevermind why I did this, or why I used "Any" and "cast". Hopefully the
macro is interesting.)
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