Dear all, I know this topic has been discussed in the past. I found at least one discussion in 2003 in guile-user@gnu.org which in the end referred to even earlier discussions in comp.lang.scheme. But still I'm confused about this and wonder if someone could help with this or point me to a discussion that resolves the following issue.
In R5RS it sais about letrec: >Semantics: The 〈variable〉s are bound to fresh locations > holding undefined values, the 〈init〉s are evaluated in the > resulting environment (in some unspecified order), each > 〈variable〉 is assigned to the result of the corresponding > 〈init〉, the 〈body〉 is evaluated in the resulting environmet [...] As I (and others) understand > scheme@(guile-user)> (letrec ((b a)(a 7)) b) > $1 = 7 should be equivalent (of course in a new scope) to: > scheme@(guile-user)> (define b #nil) > scheme@(guile-user)> (define a #nil) > scheme@(guile-user)> (set! b a) > scheme@(guile-user)> (set! a 7) > scheme@(guile-user)> b > $2 = #nil but obviously it is't. Why is b assigned to a's reference rather than it's value in letrec? ... and would it be a correct implementation of R5RS-letrec to return #nil from the letrec above? Cheers, Alex
