On May 25, 2011, at 23:05 , Alessio Stalla wrote:
On Wed, May 25, 2011 at 9:40 PM, Marco Antoniotti antoniotti.marco@disco.unimib.it wrote:
Hi I don't think there is a reasonable objection to forbid a form like ((returns-something-funcallable arg1 arg2 ... argN) 1 2 3 ... N) from "working as expected".
Me neither ;)
As Martin pointed out, if the return value of the form is a "macro" then this would have to be interpreted in the "regular" evaluation regime. As per "extending" LET there have been a lot of proposals... IMHO a nice one is to go the LOOP way :) (LETS [var <symbol> <form>]* [fun (<name> <arglist> <body>)]* [labels (<name> <arglist> <body>)]* [values <list> <form>]* IN
<body>) Of course you can add some ways of extending the syntax by having something like (def-lets-binding <tag> ...) You get the idea....
It's not about syntax, it's about a missing feature: the ability to bind a symbol's function "cell" to a value that's not known at compile time. To me, that's a limitation of the spec; given that we have funcall, it's obviously easy to implement and would be symmetrical to let. With such a feature, the gap between Lisp-1 and Lisp-2 would be effectively reduced:
(let ((list 42)) (flet ((list (compose #'nreverse #'list))) (list #'list list)))
=> (42 #<compiled-function (lambda (...) ...)>)
The code above is horrible, but you get the idea.
Yep. This has been discussed before (*)... If I remember correctly you can get almost there by specifying differently what you are doing when dealing with the OP of a form, when this is a symbol. My recollection is that it is doable and that the rationale for not allowing it is mostly to make compiler writing easier (although I think that that should be a piece of cake today).
The problem is that you have to prioritize the namespace you are searching, thus ushering in a more complex set of rules for the programmer to remember. IMHO, this is not a very good reason to "leave it out" since it has been proved over and over again that languages which increase a programmer's self esteem are also those with the absolutely most convoluted access rules ever :) Plus these languages are also very successful :)
Cheers -- Marco
(*) It's in CLL.
-- Marco Antoniotti, Associate Professor tel. +39 - 02 64 48 79 01 DISCo, Università Milano Bicocca U14 2043 http://bimib.disco.unimib.it Viale Sarca 336 I-20126 Milan (MI) ITALY
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