Staircase thought: I shouldn't have said 'precisely equivalent' since the text of the error message may differ. 'Semantically equivalent' is more correct.
On Mon, Jul 8, 2019 at 11:17 AM David Storrs <david.sto...@gmail.com> wrote: > Note that in many cases it can be better to use a contract as opposed to > an explicit check. For example, you could replace this: > > (define (feed-animals cow sheep goose cat) > (if (not (eq? goose 'goose)) > (raise-argument-error 'feed-animals "'goose" 2 cow sheep goose cat) > "fed the animals")) > > With this, which is precisely equivalent: > > (define/contract (feed-animals cow sheep goose cat) > (-> any/c any/c 'goose any/c any) > "fed the animals") > > > Or maybe you want to verify that neither cow, sheep, nor cat are also > goose: > > (define/contract (feed-animals cow sheep goose cat) > (-> (not/c 'goose) (not/c 'goose) 'goose (not/c 'goose) any) > "fed the animals") > > Or, maybe you can accept either a symbol or a string for goose: > > (define/contract (feed-animals cow sheep goose cat) > (-> any/c any/c (or/c 'goose "goose") any/c any) > "fed the animals") > > Or maybe do that case-insensitively (I'm getting rid of the excess > arguments for brevity): > > (define/contract (feed-animals goose) > (-> (compose1 (curry string-ci=? "goose") ~a) any) > "fed the animals") > > Same as above, but let's insist that the return value be a non-empty > string: > > (define/contract (feed-animals goose) > (-> (compose1 (curry string-ci=? "goose") ~a) non-empty-string?) > "fed the animals") > > If you really want to get nuts then you can do all kinds of inter-argument > checking in a contract. Here's an actual contract that I use in my > database layer, for the 'upsert-rows' function: > > (define symbol-string? (or/c symbol? string?)) > (define false-or-unsupplied? (or/c false? unsupplied-arg?)) > > (define/contract (upsert-rows #:table table-name > #:rows rows > #:conflict-clause conflict-clause > #:db [conn #f] > #:fields-to-update [fields-to-update #f] > ) > (->i (#:table [table symbol-string?] > #:rows [rows (or/c (hash/c symbol-string? any/c) > (listof (hash/c symbol-string? > any/c)))] > #:conflict-clause [conflict-clause (or/c #f 'FAIL symbol-string?)] > ; 'FAIL is redundant with `symbol-string?`. It's there for clarity. > ) > ( > #:db [db connection?] > #:fields-to-update [fields-to-update (or/c #f (non-empty-listof > symbol-string?))] > ) > ; If conflict clause is 'FAIL then fields-to-update must be #f or > unsupplied > ; If conflict clause is #f then fields-to-update must be #f or > unsupplied > ; If conflict clause is NOT #f then fields-to-update must be a list > > #:pre (conflict-clause fields-to-update) > (or (and (equal? 'FAIL conflict-clause) > (false-or-unsupplied? fields-to-update)) > (and (false? conflict-clause) (false-or-unsupplied? > fields-to-update)) > (and conflict-clause (list? fields-to-update))) > any) > ...code...) > > > > > > On Fri, Jul 5, 2019 at 1:49 PM Kevin Forchione <lyss...@gmail.com> wrote: > >> Hi guys, >> Been adding raise-argument-error to my functions to catch errors and have >> noticed that the 2nd version of the form doesn’t actually list the other >> arguments - even for the example in the docs: >> >> >(define (feed-animals cow sheep goose cat) >> (if (not (eq? goose 'goose)) >> (raise-argument-error 'feed-animals "'goose" 2 cow sheep goose cat) >> "fed the animals")) >> >(feed-animals 'cow 'sheep 'dog ‘cat) >> >> . . feed-animals: contract violation >> expected: 'goose >> given: 'dog >> argument position: 3rd >> other arguments...: >> > >> >> Is this form recommended? I’ve noticed that the documentation says some >> of the error forms have been deprecated. >> >> -Kevin >> >> -- >> 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. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/racket-users/91E9AD52-8F17-4BC3-98AB-5E43FFABC9DF%40gmail.com >> . >> For more options, visit https://groups.google.com/d/optout. >> > -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAE8gKodZ96HuYC0uL59hRfehmNi05_qxYWA-3LjXok%3DspG-6vw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
