Comments on: Defining custom literals in Chicken Scheme http://4.flowsnake.org/archives/49 A Pythoneer's adventures with Chicken Scheme. ^_^ And more. Fri, 21 Nov 2008 05:55:13 +0000 http://wordpress.org/?v=2.6.2 By: Graham Fawcett http://4.flowsnake.org/archives/49#comment-33 Graham Fawcett Mon, 28 Jan 2008 14:08:36 +0000 http://4.flowsnake.org/archives/49#comment-33 (string->number (read-number port)) seems like overkill, since your syntax expression is space-delimited. You could just use (read port), which would parse the expression, returning (in this case) a numeric literal. To catch bad inputs (non-numbers), you could use (ensure number? (read port)) which will throw an error if the value is anything non-numeric. Mind you, this would also allow expressions like "-234" and "3.1" to be parsed. You could trap it with (ensure (conjoin fixnum? positive?) (read port)), where (conjoin ...) takes a set of predicates and combines them in the "and" sense. It's great to see someone blogging about some down-and-dirty Chicken. Keep it up! :-) (string->number (read-number port)) seems like overkill, since your syntax expression is space-delimited. You could just use (read port), which would parse the expression, returning (in this case) a numeric literal.

To catch bad inputs (non-numbers), you could use (ensure number? (read port)) which will throw an error if the value is anything non-numeric.

Mind you, this would also allow expressions like "-234" and "3.1" to be parsed. You could trap it with (ensure (conjoin fixnum? positive?) (read port)), where (conjoin ...) takes a set of predicates and combines them in the "and" sense.

It's great to see someone blogging about some down-and-dirty Chicken. Keep it up! :-)

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