Comments on: SICP section 4.2.2 http://eli.thegreenplace.net/2007/12/25/sicp-section-422/ Eli Bendersky's personal website Fri, 21 Nov 2008 22:37:01 +0000 http://wordpress.org/?v=2.6.2 By: eliben http://eli.thegreenplace.net/2007/12/25/sicp-section-422/#comment-106614 eliben Tue, 05 Feb 2008 16:19:36 +0000 http://eli.thegreenplace.net/2007/12/25/sicp-section-422/#comment-106614 Flávio, but what practical use would this have ? I suppose it's possible to envision being passed such a true/false list to choose from two lists, but I would find the "map on if" approach obscure, and would definitely encapsulate it into something more legible. CL and Scheme can't do this anyway, so I don't think it's too important a need :-) Flávio, but what practical use would this have ?

I suppose it’s possible to envision being passed such a true/false list to choose from two lists, but I would find the “map on if” approach obscure, and would definitely encapsulate it into something more legible.

CL and Scheme can’t do this anyway, so I don’t think it’s too important a need :-)

]]> By: Flávio Cruz http://eli.thegreenplace.net/2007/12/25/sicp-section-422/#comment-106492 Flávio Cruz Tue, 05 Feb 2008 10:43:21 +0000 http://eli.thegreenplace.net/2007/12/25/sicp-section-422/#comment-106492 One possible use of "if" or "unless" as high order procedures would be something like this: (map if '(true false true) '(2 3 4) '(3 6 2)) -> '(2 6 4) map would build a list selecting an element of the second or third list depending on the values of the first list. One possible use of “if” or “unless” as high order procedures would be something like this:

(map if ‘(true false true) ‘(2 3 4) ‘(3 6 2)) -> ‘(2 6 4)

map would build a list selecting an element of the second or third list depending on the values of the first list.

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