Hi!
I am trying to write a macro, which checks the name of an argument for
presence a substring. This is not the main purpose of the macro, but I want
to do different things depending on the substring being contained or not
contained.
Here is what I've got so far:
~~~~~
;; A macro to get the identifier name as string, shamelessly copied from
StackOverflow and renamed:
(define-syntax identifier-name->string
(lambda (stx)
(syntax-case stx ()
((_ id)
(identifier? #'id)
(datum->syntax #'id (symbol->string (syntax->datum #'id)))))))
;; And the actual macro I want to write:
(define-syntax define-api-route
(lambda (stx)
(syntax-case stx (GET HEAD POST PUT DELETE CONNECT OPTIONS TRACE PATH)
[(_ route GET my-content-type)
(string-contains? (identifier-name->string (syntax route)) "abc")
(println "abc is in the identifier name")])))
~~~~~
With this, Racket will complain, that I am referencing an identifier before
its definition:
~~~~~
> (define-syntax identifier-name->string
(lambda (stx)
(syntax-case stx ()
((_ id)
(identifier? #'id)
(datum->syntax #'id (symbol->string (syntax->datum #'id)))))))
>
(define-syntax define-api-route
(lambda (stx)
(syntax-case stx (GET HEAD POST PUT DELETE CONNECT OPTIONS TRACE PATH)
[(_ route GET my-content-type)
(string-contains? (identifier-name->string (syntax route)) "abc")
(println "abc is in the identifier name")])))
> (define-api-route abc/abc/abc GET
application/json)
; string-contains?: undefined;
; cannot reference an identifier before its definition
; in module: top-level
; internal name: string-contains?
; [,bt for context]
~~~~~
If I take away the (syntax ...) in the guard expression however, it will
also not work, as template variables may only occur in syntax:
~~~~~
> (define-syntax
define-api-route
(lambda
(stx)
(syntax-case stx (GET HEAD POST PUT DELETE CONNECT OPTIONS TRACE
PATH) [(_ route GET
my-content-type)
(string-contains? (identifier-name->string route)
"abc")
(println "abc is in the identifier name")])))
; readline-input:19:52: route: pattern variable cannot be used outside of a
; template
; in: route
; [,bt for context]
~~~~~
I have also tried loads of other stuff, but I cannot find a way to:
1. get the identifier name of route, whatever the user has as route (not a
string yet!)
2. check inside the guard expression, whether the identifier name contains
a certain substring
3. based on that substring call other macros to do the actual job of
defining an API route
Can you help me writing this macro?
It would also be great, if the macro was portable, meaning that it is
usable from any Scheme.
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