Function: SHARPL-READER

Documentation

Reader macro for simple lambdas. This read macro reads exactly one form and serves to eliminate the 'boiler' plate text from such lambdas and write only the body of the lambda itself. If the form contains any references to varibales named !1, !2, !3, !n etc. these are bound to the Nth parameter of the lambda. Examples: #L(foo) ==> (lambda () (foo)). #L(foo !1) ==> (lambda (!1) (foo !1)) #L(foo (bar !2) !1) ==> (lambda (!1 !2) (foo (bar !2) !1)) All arguments are declared ignorable. So if there is a reference to an argument !X but not !(x-1) we still take X arguments, but x - 1 is ignored. Examples: #L(foo !2) ==> (lambda (!1 !2) (declare (ignore !1)) (foo !2)) We can specify exactly how many arguments to take by using the read macro's prefix parameter. NB: this is only neccessary if the lambda needs to accept N arguments but only uses N - 1. Example: #2L(foo !1) ==> (lambda (!1 !2) (declare (ignore !2)) (foo !1))

Source

(defun sharpL-reader (stream subchar min-args)
  "Reader macro for simple lambdas.

This read macro reads exactly one form and serves to eliminate
the 'boiler' plate text from such lambdas and write only the body
of the lambda itself. If the form contains any references to
varibales named !1, !2, !3, !n etc. these are bound to the Nth
parameter of the lambda.

Examples:

#L(foo) ==> (lambda () (foo)).

#L(foo !1) ==> (lambda (!1) (foo !1))

#L(foo (bar !2) !1) ==> (lambda (!1 !2) (foo (bar !2) !1))

All arguments are declared ignorable. So if there is a reference
to an argument !X but not !(x-1) we still take X arguments, but x
- 1 is ignored. Examples:

#L(foo !2) ==> (lambda (!1 !2) (declare (ignore !1)) (foo !2))

We can specify exactly how many arguments to take by using the
read macro's prefix parameter. NB: this is only neccessary if the
lambda needs to accept N arguments but only uses N - 1. Example:

#2L(foo !1) ==> (lambda (!1 !2) (declare (ignore !2)) (foo !1))"
  (declare (ignore subchar))
  (let* ((form (read stream t nil t))
         (lambda-args (loop
                         for i upfrom 1 upto (max (or min-args 0)
                                                  (highest-bang-var form))
                         collect (make-sharpl-arg i))))
    `(lambda ,lambda-args
       , (when lambda-args
           `(declare (ignorable ,@lambda-args)))
       ,form)))