Thanks for your prompt and clear reply. I admit I don't fully understand the map? argument. Just by trying out I know that for my purposes I always have to provide true for the map? argument. Meanwhile I insert the namespace-set-variable-value! line with true map? argument, as you suggest. Thanks again, Jos
_____ From: [email protected] [mailto:[email protected]] On Behalf Of Jens Axel Søgaard Sent: jueves, 27 de agosto de 2015 17:35 To: Jos Koot Cc: Racket-Users List Subject: Re: [racket-users] namespace-undefine-variable! question The issue here is whether the namespance's identifier mapping is used or not. The documentation for namespace-undefine-variable! says: Removes the sym variable, if any, in the top-level environment of namespace in its <file:///Applications/Racket%20v6.2/doc/reference/syntax- model.html?q=namespace-va#%28tech._base._phase%29> base phase. The namespace’s <file:///Applications/Racket%20v6.2/doc/reference/syntax- model.html?q=namespace-va#%28tech._identifier%29> identifier mapping (see Namespaces <file:///Applications/Racket%20v6.2/doc/reference/syntax- model.html?q=namespace-va#%28part._namespace-model%29> ) is unaffected. We can see that list is use the identifier mapping by changing the second argument of namespace-variable-value to #f. #lang racket (define ns (make-base-namespace)) (namespace-variable-value 'list #f (λ () 'not-found) ns) which evaluates to 'not-found. Inserting your own non-imported value for list makes the identifier non- imported and has the happy side-effect of making namespace-undefined-variable! capable of removing the binding from namespace. In some sense namespace-undefined-variable! miss an map? argument. Your solution: insert, then undefine seem to be the best solution for now. /Jens Axel you n 2015-08-27 16:53 GMT+02:00 Jos Koot <[email protected]>: The following works: #lang racket/base #;1 (define ns (make-base-namespace)) #;2 (namespace-variable-value 'list #t (λ () 'not-found) ns) ; -> #<procedure:print-syntax-width> #;3 (namespace-set-variable-value! 'list 'whatever (λ () #f) ns) #;4 (namespace-undefine-variable! 'list ns) #;5 (namespace-variable-value 'list#t (λ () 'not-found) ns) ; -> not-found But when I omit line 3 it does not work: #lang racket/base #;1 (define ns (make-base-namespace)) #;2 (namespace-variable-value 'list #t (λ () 'not-found) ns) ; -> #<procedure:list> #;4 (namespace-undefine-variable! 'list ns) ;-> error namespace-undefine-variable!: given name is not defined ; name: list This I did with: Welcome to DrRacket, version 6.2.0.5--2015-07- 06(d6fa581/a) [3m]. Code in the definitions window. The problem is not typical for 'list only. The same happens with (at least some) other variables of a base-namespace. I have no clue why commenting out line 3 gives an error. Do I misinterpret the docs on namespaces? Thanks, Jos PS I use a base-namespace in a toy interpreter. It allows me to easily borrow all variables from a base-namespace. But some of them I want to undefine. -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout. -- -- Jens Axel Søgaard -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
