Hi,
I'm trying to write a simple javascript DSL, and got stuck in the macros
:). (I'm coming from lisp macros) Take for example this one:
(define-syntax js
(ir-macro-transformer
(lambda (expr inject compare)
(let ((body (cdr expr)) (next (cadr expr)))
(printf "next=~a~n" next)
(cond
[(string? next) (string-append "\"" next "\"")]
[(number? next) (number->string next)]
[(null? next) ""]
[(list? next) `(string-append (js ,(car next)) "(" ")")]
)))))
It is supposed to handle numbers and function calls, without building the
parameter list in the function calls.
CSI> (js 1)
next=1
"1"
CSI> (js (1 2 3))
next=(1 2 3)
next=1
"1()"
However, when trying to build the parameter list I get and error which I
don't understand:
(define-syntax js
(ir-macro-transformer
(lambda (expr inject compare)
(let ((body (cdr expr)) (next (cadr expr)))
(printf "next=~a~n" next)
(cond
[(string? next) (string-append "\"" next "\"")]
[(number? next) (number->string next)]
[(null? next) ""]
[(list? next) `(string-append (js ,(car next)) "(" (apply
string-append (map js ,(cdr next))) ")")]
)))))
CSI> (js (1 2 3))
next=(1 2 3)
next=1
Error: unbound variable: js
[ inspect ]
Restarts:
0: [ABORT] Return to SLIME's top level
Backtrace:
0: <eval> [ more... ] (map248 js245 (2 3))
1: <eval> [ more... ] (apply247 string-append246 (map248 js245 (2 3)))
2: <eval> [ more... ] (string-append246 (js245 1) "(" (apply247
string-append246 (map248 js245 (2 3))) ")")
3: <syntax> (2 3)
4: <syntax> (map248 js245 (2 3))
5: <syntax> (apply247 string-append246 (map248 js245 (2 3)))
6: <eval> [ more... ] (number->string next)
7: <eval> [ more... ] (number? next)
8: <eval> [ more... ] (printf "next=~a~n" next)
9: <eval> [ more... ] (cadr expr)
10: <eval> [ more... ] (cdr expr)
11: <syntax> (js245 1)
12: <syntax> (string-append246 (js245 1) "(" (apply247
string-append246 (map248 js245 (2 3))) ")")
13: <eval> [ more... ] (cdr next)
14: <eval> [ more... ] (##sys#list (##core#quote map) (##core#quote js)
(cdr next))
15: <eval> [ more... ] (##sys#list (##core#quote apply) (##core#quote
string-append) (##sys#list (##core#quote map) (##core#quote js) (cdr next)))
So, my questions are:
1/ Why is "js" not bound in the second example? I also tried to use
letrec-syntax but with same result.
2/ Are there other ways to achieve what I want?
3/ I also tried to use syntax-rules, but from what I understood this is not
possible, because you can't execute arbitrary expressions (in this case a
cond) at macroexpansion time. Am I right here?
Thanks,
Răzvan
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