A "Let" statement that sets a bunch of variables

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Post #154,245 by tablizer 5/7/04 3:20:20 PM Reply	A "Let" statement that sets a bunch of variables ________________ oop.ismad.com
Post #154,258 by ben_tilly 5/7/04 5:11:37 PM Reply	Ah, that is because let is a special form There are very few exceptions in the language. That is one of them. When you see something like: \n(let ((First (gensym "FIRST-"))\n (Second (gensym "SECOND-"))\n (Sum (gensym "SUM-")))\n .\n .\n .\n)\n what is happening is that the expression is evaluated from the outside in. So Lisp notices that let is a special form, and the following expression is parsed according to the rules for that form. Very, very few parts of the language are going to change rules like that. The other place where you get tripped up is that that macros or special forms can decide whether or not a particular term should be evaluated (or possibly should be evaluated multiple times). But just think about how you would write an if test, or a loop without that facility, and you see why it is needed. So yes. let is going to be special in that way. And it is an inconsistency. But I can't think of a single language that doesn't have inconsistencies which are as big or bigger. Cheers, Ben To deny the indirect purchaser, who in this case is the ultimate purchaser, the right to seek relief from unlawful conduct, would essentially remove the word consumer from the Consumer Protection Act - [link\|http://www.techworld.com/opsys/news/index.cfm?NewsID=1246&Page=1&pagePos=20\|Nebraska Supreme Court]
Post #154,259 by ChrisR 5/7/04 5:31:05 PM Reply	Not to get in too deep... ...if i haven't already, but let is a macro in Scheme of the form: (let (let ((var val)) body) => ((lambda (var) body) val) Basically a form of a bound variable, with a macro for syntactic sugar.

Why I find LISP hard to read - (tablizer) - (25) - May 7, 2004, 02:35:30 AM EDT

Scheme to the rescue - (ChrisR) - May 7, 2004, 10:27:59 AM EDT

Care to offer an example where there is some ambiguity? - (ben_tilly) - (20) - May 7, 2004, 10:39:07 AM EDT

Allowed in CLOS but not in Scheme - (ChrisR) - (16) - May 7, 2004, 10:46:36 AM EDT

Care to show me the example? - (ben_tilly) - (15) - May 7, 2004, 11:53:03 AM EDT

Lisp is a family of languages - (ChrisR) - (14) - May 7, 2004, 12:35:17 PM EDT

Rethinking, reloading. :-) - (ChrisR) - (13) - May 7, 2004, 01:02:43 PM EDT

Thanks for the confirmation - (ben_tilly) - (1) - May 7, 2004, 02:24:26 PM EDT

Special forms - (ChrisR) - May 7, 2004, 02:29:59 PM EDT

just trying to learn - (tablizer) - (10) - May 7, 2004, 03:32:51 PM EDT

As far as I understand - (ChrisR) - (9) - May 7, 2004, 03:59:52 PM EDT

More on s-expressions - (ChrisR) - May 7, 2004, 08:17:02 PM EDT

Downsides of flexibility - (tablizer) - (7) - May 10, 2004, 03:25:50 PM EDT

Less flexible = good? - (ChrisR) - (6) - May 10, 2004, 04:34:10 PM EDT

Dejavu - (FuManChu) - (2) - May 11, 2004, 12:44:10 PM EDT

I like big apps and I can not lie. - (ChrisR) - May 11, 2004, 04:19:46 PM EDT

Language de jour - (ChrisR) - May 11, 2004, 04:26:02 PM EDT

Standards versus flexibility - (tablizer) - (2) - May 11, 2004, 02:34:04 PM EDT

One of the problem is that by the time a comprehensive... - (ChrisR) - (1) - May 11, 2004, 03:10:56 PM EDT

You are probably right, but I'll be long retired by then - (tablizer) - May 11, 2004, 06:57:45 PM EDT

A "Let" statement that sets a bunch of variables -NT - (tablizer) - (2) - May 7, 2004, 03:20:20 PM EDT

Ah, that is because let is a special form - (ben_tilly) - (1) - May 7, 2004, 05:11:37 PM EDT

Not to get in too deep... - (ChrisR) - May 7, 2004, 05:31:05 PM EDT

OT: Why is this in Scripting? -NT - (pwhysall) - (2) - May 8, 2004, 12:27:54 AM EDT

oh oh, I smell another fight over definition of "scripting" -NT - (tablizer) - (1) - May 9, 2004, 02:19:52 AM EDT

:-) -NT - (pwhysall) - May 9, 2004, 03:22:17 AM EDT

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