Thanks Taylan, > On 18. Mar 2020, at 07:12, Taylan Kammer <taylan.kam...@gmail.com> wrote: > > On 18.03.2020 00:50, Massimiliano Gubinelli wrote: >> (let ((a (values "a" "b" "c"))) a) > > The result of (values x y z) is not a kind of object that contains three > values (like a list or vector). It's three separate values that would need > to be put into three separate variables. But you're only naming one variable > (a). So strictly speaking the code is "wrong". > > In Guile 1.8, multiple values were actually put into some special kind of > object (which was not very efficient) so code like that still somehow worked > even thought it's technically wrong. > > Starting from Guile 2.0, providing multiple values in a context where only > one is expected causes the extra values to be ignored. > >
I understand the point but then it comes to the problem how to handle this in macros. For example if bar is a proceduce which returns multiple values and I have a macro "my-macro" which wraps the call with some initialization and finalization code and I write (my-macro (bar)) how to write this macro without knowing if bar is returning multiple values or not? For example I would like the code above to expand into (begin (initialization-code) (let ((ret (bar))) (finalization-code) ret)) But this does not work as shown by the example above. How to implement this macro correctly? best Max > Happy to answer further questions about this. Multiple-values can be a > tricky concept to grasp because most other programming languages don't have > it. > > - Taylan
