clarify use of define in internal definitions about r7rs-pico-spec HOT 5 CLOSED

How about this way to do mutually recursive:

(define a
  (lambda (x)
    (define b
      (lambda (x) (a (- x 1))))
    (if (< x 1) 0
	(b (- x 1)))))
(a 3)

from r7rs-pico-spec.

I agree that it could be more clear. From the denotational semantics, if "ε ∈ F" is the only case where a variable is defined in the environment of its evaluation for define.

What kind of code were you thinking of for this?
The following would be an error is R7RS (not necessarily signaled), but by the denotational semantics (assuming I got them the way I wanted) it should result in a being 4 in Pico Scheme:

(define a (+ 1 1))
(define a (+ a a))

but this is because a define put a variable in all statements that are after the define in the body.

from r7rs-pico-spec.

In fact I want to know how to define a recursive function? Is it possible using define in a body?

(define doit (lambda (a b c) (if a b (doit (f a b c) (g a b c) (h a b c)))))

The example you gave in the answer is ambiguous. But I understand that the answer is yes.

from r7rs-pico-spec.

Yes, it is possible to do a recursive function anywhere you can use a define. For what it is worth, there is no straight forward way to do mutually recursive functions (a calls b, b calls a). (I think (define a ...) (define b ...) (define a ...) would work but I am not sure I recommend doing that).

I will look at sections 5.2.1 and 5.2.2 and see if I can make some of this more clear in a pull request.

from r7rs-pico-spec.

I agree that mutually recursive function are not straight forward with pr7 and also agree that your trick is ugly.

While checking for how to improve 5.2.1 and 5.2.2, also mentionning the restriction on mutually recursive functions would help.

from r7rs-pico-spec.