Mark H Weaver <m...@netris.org> writes: > David Kastrup <d...@gnu.org> writes: >> >> A list in dotted tail position is evaluated via (map ... eval) rather >> than (eval ...). I don't see much of a problem with that. > > No, it's worse than that. I think you failed to understand my point, > so let me try again. You propose that (f . x) should be equivalent to > (apply f x).
When x is not a pair or (). > Therefore, (f . (g x y)) should also be equivalent to (apply f (g x > y)). But (g x y) is a pair. > To make this more concrete, suppose 'f' is 'vector and 'g' is 'list': > > (vector . (list 1 2)) (list 1 2) is a pair (with the car list and the cdr (1 2)). > If we were to adopt your proposal, users would naturally expect this to > evaluate to #(1 2). However, the evaluator sees (vector list 1 2) and > thus produces a vector of three elements: #(#<procedure list _> 1 2). Sure. > In summary, your proposed syntax could only be detected if the dotted > tail happened to be an atom. () is an atom, but it is already treated differently. > Scheme has a very useful property which your proposed syntax would > destroy: any valid expression can be substituted for any other valid > expression, and the result has the same meaning except for the > substitution. guile> (display . (close (current-output-port))) #<primitive-procedure close>guile> Now try (define x (close (current-output-port))) (display . x) Good luck. The context already decides what a valid expression is. Not everything looking like one is treated like one. -- David Kastrup
