PLT Scheme sort function

PLT Scheme guide says that it's implemented sort function is able to sort a list according to an extarcted value using a lambda function. link text

The guide provides an unworking code example of this-

(sort '(("aardvark") ("dingo") ("cow") ("bear"))
      #:key car string<?)

Which returns an error.

How is this function is supposed to be calles so that it will actually sort a list acc开发者_开发知识库ording to values calculated by a given function?

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It works for me. Which Scheme dialect are you using? And what error do you get? In my DrScheme setup, I have "Module" selected from the dropdown at the bottom left, and

 #lang scheme

run in the top window.

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My guess is similar to Neil's: first, you should be using a recent version of PLT for that. Try to run this when DrScheme is in the Module language (the first choice in the language selection dialog):

#lang scheme
(sort '(("aardvark") ("dingo") ("cow") ("bear"))
      #:key car string<?)

Second, that syntax uses keyword arguments, so if you're using some language like R6RS or R5RS or Pretty Big etc, then you won't be able to use sort with a keyword like that. (It's best to just stick with the module language and #lang scheme.)