Olin.Shivers@CENTRO.SOAR.CS.CMU.EDU (07/24/88)
(let ([null? null?]) (define-macro! nil? (x) `(,null? ,x)) ; note comma before null? I don't use the Scheme's you use, but I think I can see at least one problem with this macro: functions are *not* defined in Scheme to be self-evaluating like, for example, integers are. So instead of: ,null? you need: ',null? As in: (let ((null? null?)) (define-macro! nil? (x) `(',null ,x))) -Olin
dorai@titan.rice.edu (Dorai Sitaram) (07/25/88)
`define-macro!', the form used to define macros in older versions of Chez Scheme [TM, Cadence Research Systems] is also provided in the current version (along with the fancier `extend-syntax'/`with'). However, the older version (v.1.1, 1985) seems more powerful (expressive) than the current one (v.2.0.3, 1987)! In the old case, it is possible to specify not just text but closures in a "macro"'s expansion pattern. For example, the following almost pointless program, (let ([null? null?]) (define-macro! nil? (x) `(,null? ,x)) ; note comma before null? works fine in v.1.1, `nil?' being a macro version of `null?'. As motivation for using the closure `null?' rather than the variable `null?' in the above macro expansion, one might consider that the global variable `null?' can now be redefined to something else, but `nil?' will always test for nil-ness. This ruse doesn't work in v.2.0.3: The program (nil? 7) yields the diagnostic: Error: nonsensical application (#<procedure null?> 7). Anyone know why Cadence (Dybvig?) thought fit to do away with the old Chez's more powerful macros? {I don't know Cadence's e-mail address.} --dorai ps: It might be argued that there might be newer ways (possibly using `extend- syntax'/`with') to get the effect described above, if not with the same program fragment. Nope. There just doesn't seem a way to get closures in the expansion pattern in new Chez.
gateley@mips.csc.ti.com (John Gateley) (07/26/88)
In article <1709@kalliope.rice.edu> dorai@titan.rice.edu (Dorai Sitaram) writes: >`define-macro!', the form used to define macros in older versions of >Chez Scheme [TM, Cadence Research Systems] is also provided in the current >version (along with the fancier `extend-syntax'/`with'). However, the older >version (v.1.1, 1985) seems more powerful (expressive) than the current one >(v.2.0.3, 1987)! Just a side note: you seem to be saying that the define-macro! form is more powerful than extend-syntax and with. This is not true. Extend-syntax can be used to do 3-d programming (the technique you describe in your message), and any macro. It is completely general. John Gateley p.s. Extend-syntax was created by Eugene Kohlbecker.