--- On Thu, 5/3/12, Hendrik Boom <hend...@topoi.pooq.com> wrote: > From: Hendrik Boom <hend...@topoi.pooq.com> > Subject: Re: [racket] Wikipedia article update > To: users@racket-lang.org > Date: Thursday, May 3, 2012, 8:51 PM > On Thu, May 03, 2012 at 05:02:08PM > -0700, John Clements wrote: > > > > and updated the Wikipedia page to reflect my better > understanding. The text now reads: > > > > "The earliest Lisp macros took the form of FEXPRs, > function-like operators whose inputs were not the values > computed by the arguments but rather the syntactic forms of > the arguments, and whose output were values to be used in > the computation. In other words, FEXPRs were implemented at > the same level as EVAL, and provided a window into the > meta-evaluation layer. This was generally found to be a > difficult model to reason about effectively [6]. > > An alternate, later facility was called DEFMACRO, a > system that allowed programmers to specify source-to-source > transformations that were applied before the program is > run." > > FEXPRs were used to implement things like COND, QUOTE, and > the like. > It would be difficult to use macros instead of FEXPRs for > these, > unless they were built into the interpreter. And > FEXPRs were the > mechanism by which this was done. >
FEXPRs are still used in Pico Lisp and NewLisp. They are simply functions whose arguments aren't evaluated. > (define-macro (foo x) x) (lambda-macro (x) x) > (foo (* 2 3 4)) (* 2 3 4) > (list? (foo (* 2 3 4))) true > (define-macro (bar x) (println x) (+ x 1000)) (lambda-macro (x) (println x) (+ x 1000)) > (bar (* 2 3)) (* 2 3) ERR: value expected in function + : x called from user defined function bar > (define-macro (bar x) (+ (eval x) 1000)) (lambda-macro (x) (+ (eval x) 1000)) > (bar (* 2 3)) 1006 ____________________ Racket Users list: http://lists.racket-lang.org/users
