You may wish to study Alexis’s struct updater package: https://github.com/lexi-lambda/struct-update <https://github.com/lexi-lambda/struct-update>
> On May 26, 2018, at 11:46 AM, David Storrs <david.sto...@gmail.com> wrote: > > Hi folks, > > I am becoming more converted to the way of structs vs hashes as time goes on > and so I sat down to write a macro that would generate functional setters as > a convenience. Code is at bottom of email; I'd appreciate suggestions on how > to improve it, in particular better ways of handling macros that have > multiple optional parts, e.g.: > > (struct foo (bar baz jaz)) > (make-functional-setter foo bar) > (make-functional-setter foo baz string?) > (make-functional-setter foo jaz path-string? path-string->string) > > I've seen this handled in two ways: > > 1) define-syntax-class with multiple (pattern ...) clauses, which renders the > parsing cleaner and easier to understand. Handling missing parts is still an > issue, since using an attribute that wasn't matched is a syntax error, so my > questions: > > A) Is there a way to test if a syntax class has a particular attribute before > trying to use it? > > B) Alternatively, is there a way to create a null syntax object that expands > to nothing? Not (void), not "", literally nothing. Then I could have each > pattern bind all the attributes via #:with and just have some of them be > blank. > > > 2) Alternatively, macros with optional parts can be handled by a series of > test cases in a syntax-parse, one for each option. That ends up with a lot > of copy/pasted code between the segments. I'm getting around this via > re-parsing but that feels clumsy. What is the better way? > > > 3) There's something I'm not understanding about providing this thing. I > have it in a file called make_functional_setter.rkt: > > #lang racket > (require (for-syntax racket/syntax syntax/parse)) > (provide make-functional-setter) > ; code and comments for make-functional-setter, see bottom of email > > When I (require "../make_functional_setter.rkt") on the CLI racket shell, > everything works great. As soon as I try to require it into a file, it fails: > > Contents of file test.rkt: > > #lang racket > (struct bar (a b)) > (require "../make_functional_setter.rkt") > (make-functional-setter bar a) > (make-functional-setter bar b path-string? ~a) > > When I do "racket test.rkt" on the command line, I get the following > exception: > > bar?: unbound identifier in module > context...: > #(2082 module test 0) #(3901 module) #(3902 module struct 0) #(25633 macro) > #(25639 use-site) #(25818 local) #(25820 intdef) > other binding...: > #f > #(2081 module) #(2082 module test 0) > in: bar? > context...: > standard-module-name-resolver > > I've been through this in the DrRacket macro stepper but that hasn't helped > me any. (It rarely does.) > > I'm assuming it's a phase issue, so I've played around with for-syntax, > for-template, and for-meta but apparently I do not understand phases well > enough. > > What could be causing this? > > > > I've been going through all the macro- and syntax-related docs that I can > find, but there's a lot of them and they take a few re-reads to sink in, so > there's probably something exactly for this that I haven't seen. > > Code is below and at > https://gist.github.com/dstorrs/a53ec8736551eb5745d1d5fd265b5062 > <https://gist.github.com/dstorrs/a53ec8736551eb5745d1d5fd265b5062> in case > Gmail mangled the formatting. > > > ;; make-functional-setter: macro for generating non-mutating field > ;; setter functions for a struct > ;; > ;; Define a struct: (struct book (title current-page filepath) #:transparent) > ;; > ;; Generate 'set-book-title', 'set-book-current-page', and > 'set-book-filepath'. > ;; All of these take two to four arguments: the 'book' struct to update, the > ;; new value, an optional contract, and an optional wrapper function. > ;; > ;; (make-functional-setter book title) > ;; (make-functional-setter book current-page exact-positive-integer?) > ;; (make-functional-setter book filepath path-string? > path-string->string) > ;; > ;; Details: > ;; set-book-title accepts any value, regardless of sensibility > ;; set-book-current-page accepts only exact-positive-integer?s, else > contract violation > ;; set-book-filepath accepts only path-string?s, converts to string > before storing > ;; > ;; Examples: > ;; (define b (book "Foundation" 297 (build-path "/foo/bar"))) > ;; b ; (book "Foundation" > 297 "/foo/bar") > ;; (set-book-title b (hash)) ; (book (hash) 297 > "/foo/bar") > ;; (set-book-current-page b 99) ; (book "Foundation" > 99 "/foo/bar") > ;; (set-book-current-page b 'x) ; ERROR! Contract > violation > ;; (set-book-filepath b (build-path "/foo")) ; (book "Foundation" > 297 "/foo") > ;; > (define-syntax (make-functional-setter stx) > (syntax-parse stx > ; First, grab the name of the struct and the field we're making > ; this for. We'll build some stuff here then re-parse instead of > ; copy/pasting for every pattern match > [(_ type-name field-name ignored ...) > (with-syntax* ([func-name (format-id #'type-name "set-~a-~a" > #'type-name #'field-name)] > [func-header #'(func-name the-struct val)] > [definer #'define] > [type-pred (format-id #'type-pred "~a?" #'type-name)] > [func-body #'(struct-copy type-name the-struct > [field-name val])] > ) > (syntax-parse stx > [(_ _ _) #'(definer func-header func-body)] > [(_ _ _ field-contract:expr ignored ...) > (with-syntax ([definer #'define/contract] > [func-contract #'(-> type-pred field-contract > type-pred)]) > (syntax-parse stx > [(_ _ _ _) #'(definer func-header func-contract func-body)] > [(_ _ _ _ wrapper:expr) > #'(definer func-header > func-contract > (struct-copy type-name the-struct [field-name (wrapper > val)]))]))]))])) > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com > <mailto:racket-users+unsubscr...@googlegroups.com>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. 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