# Macro in Racket language? **URL:** \ **Category:** Questions & Answers\ **Tags:** macro\ **Created:** [February 13, 2023, 12:51pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709 "2023-02-13T12:51:48Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [February 13, 2023, 12:51pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/1 "2023-02-13T12:51:49Z")
```scheme > (version) "8.8" > (require (for-syntax racket/base)) > (define-syntax-rule (make-module n (l ...) i b) (module n racket/base (require l ...) (provide i) (define i b))) > (make-module t () x 1) string:1:20: ?: literal data is not allowed; no #%datum syntax transformer is bound at: 1 [,bt for context] > (make-module t (racket/base) x 1) ``` Anyway, the macro can be expanded successfully at last, but I don't want to import the library twice. What should I do? Or is this documented? ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [February 13, 2023, 2:08pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/2 "2023-02-13T14:08:25Z")
I think the problem is how `#%datum` is introduced. When `#%datum` is introduced it gets the lexical information from the syntax object (that needs to wrapped in `#%datum`). In the form `(make-module t () x 1)` the `1` will become `(#%datum . 1)` but the `#%datum` has lexical information from outside the `t` module. So you get the "no #%datum syntax transformer is bound" error. How to solve the problem depends on where you want `b` to get its context. One option: ```scheme (define-syntax (make-module stx) (syntax-case stx () [(_make-module n (l ...) i b) (with-syntax ([b (datum->syntax #'stx (syntax->datum #'b))]) (syntax/loc stx (module n racket/base (require l ...) (provide i) (define i b))))])) ``` ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [February 13, 2023, 2:16pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/3 "2023-02-13T14:16:10Z")
Thanks for your kind explanation, sir! But there still remains a question. Why does the error just disappear when we explicitly import the library in the `t` module? ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [February 13, 2023, 2:23pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/4 "2023-02-13T14:23:34Z")
It boils down to how `(require module-path)` works. > (require module-path) > Imports all exported bindings from the named module, > using the export name for the local identifiers. > The lexical context of the module-path form determines the > context of the introduced identifiers, a ... So in `(make-module t (racket/base) x 1)` the `racket/base` and `1` have the same lexical context. When inserted in `(require l ...)` the imported binding for `#%datum` will have the same context as `1`. And when the implicit `#%datum` is added, it will now be bound. ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [February 13, 2023, 2:27pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/5 "2023-02-13T14:27:16Z")
Thank you very much, sir! ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [February 13, 2023, 2:41pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/6 "2023-02-13T14:41:59Z")
But according to the [documentation](https://docs.racket-lang.org/reference/module.html#%28form._%28%28quote._~23~25kernel%29._module%29%29), > The module-path form must be as for [require](https://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29), and it supplies the initial bindings for the body forms. That is, it is treated like a ([require](https://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29) module-path) prefix before the forms, except that the bindings introduced by module-path can be shadowed by definitions and [require](https://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29)s in the module body forms. Is this case an exception? ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [February 13, 2023, 3:07pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/7 "2023-02-13T15:07:47Z")
In ```scheme (module n racket/base ...) ``` the context of the racket/base is "inside the module n". Likewise, in: ```scheme (module n racket/base (require racket/base) ...) ``` the context of `racket/base` is also inside module `n`, so this is fully redundant. However, in your example `(make-module t (racket/base) x 1)` the context of `racket/base` is "from outside the module n", so the bindings of `(require racket/base)` will get that context. ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [February 13, 2023, 3:09pm UTC](https://racket.discourse.group/t/macro-in-racket-language/1709/8 "2023-02-13T15:09:37Z")
Oh, I see. Sorry for bothering you!