[r6rs-discuss] letrec/letrec* violations

[leppie]

Hi

Under the documentation for letrec and letrec* the following is said [1]:
"Another restriction is that the continuation of each <init> should not be
invoked more than once." ... "Implementations may or may not detect that the
continuation of each <init> is invoked more than once. However, if the
implementation detects this, it must raise an exception with condition type
&assertion. "

1. What does 'should' imply here? (it is not required, but 'how much'
desired?)

2. Is the following an example of a such a violation?
  (letrec ((x (call/cc values))) (x list))

3. Are there any Scheme's that actually implement/detect this violation?

4. What are the reasoning behind this?

Thanks in advance

Cheers

leppie


[1]: http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-14.html#node_sec_11.4.6

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