Hi, check out guile-syntax-parse at
https://gitorious.org/guile-syntax-parse/guile-syntax-parse
(You have to patch some ice-9 routines to make this work (syntax-expression
and syntax-object? need to be in the environment - the files are included)
So by writing
#|
Syntax parse examples
|#
(use-modules (parse syntax-parse))
(use-modules (parse match-parse))
(define <list2>
(<parse-list>
#t ;; signal error if #t else record error if
#f
;; error msg if not a list
"in let decl, (symbol val) malformed"
;; error msg in case of wrong number of elements
"list must have length 2"
2)) ;; the length of the list
(define <arg2>
(<parse-list..>
#t
"not a list Bug! args are a list"
"either * and/or code1 is missing in:~% (let * code1 code ...)"
3))
(define <list>
(<parse-list..>
#t
"declaration form in let is not a list"
"Bug if this is printed"
))
;; here is an example of designing a matcher out of pieces
(define <arg2..>
(lambda (x)
(match-parse -abs ((<arg2> x) (<list> y)) ;; matchers needs declaration
x
;; if 2 args followed by a list of 0 ... elements then success
((<arg2> <list>) (list #t))
(_ (error "Bug in let macro")))))
;; here is a simple checked let form
;; Using the symbol tool
(define <sym> (<symbol> "variable decl in let"))
;;; THE MAIN MACRO
(define-syntax my-let
(syntax-parse ()
((_ (((s : <sym>) v : <list2>) ... : <list>)
code2 ... : <arg2..> )
(let ((s v) ...) code2 ...))))
We get, (line number buggs still in the codebase)
.............................................................................................
scheme@(guile-user)> (my-let a)
While compiling expression:
ERROR: error at 1, either * and/or code1 is missing in:
(let * code1 code ...)
scheme@(guile-user)> (my-let a 1)
While compiling expression:
ERROR: error at -1, declaration form in let is not a list
scheme@(guile-user)> (my-let (a 1) a)
While compiling expression:
ERROR: error at -1, in let decl, (symbol val) malformed
scheme@(guile-user)> (my-let ((1 1)) a)
While compiling expression:
ERROR: error at 4, variable decl in let, not a symbol
scheme@(guile-user)> (my-let ((a 1)) a)
$1 = 1
scheme@(guile-user)> (my-let ((a 1)) 1 a)
$2 = 1
scheme@(guile-user)> (my-let ((a 1) b) 1 a)
While compiling expression:
ERROR: error at -1, in let decl, (symbol val) malformed
.............................................................................................
We should be able to use the Parser code-base in stead of my match macro and
then this is really a small setup.
/Stefan
