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[REBOL] Re: More dialects than you think, validating function input.

From: greggirwin:mindspring at: 12-Sep-2002 9:56

Brett, et al A very good post, and related to the discussion on error handling to boot! :) I can see at least two major ways to apply this approach. 1) Parse drives the processing of the function, automatically validating the correctness of the argument block as it goes. 2) Parse is used only to validate the block at the entry point, like a precondition in a Design by Contract design, and the operation of the function is separate. You could also use parse to validate return values (i.e. as a post-condition processor). In a large system, and as more things are driven by dialects, this could prove very useful indeed. Now, does anyone have a model they use to return helpful context information when a parse operation fails? Programmers are OK with "Syntax error: expected integer!" but users are probably better served by "I understood the first part ("sell 400 shares of MSFT at"), but then I was expecting to see a monetary value for the sell price (e.g. $50.00), and I didn't, so I couldn't process your request. I'm sorry for any inconvenience this might cause you. Have a nice day." Or maybe just "No sell price was specified in your request." or even a prompt for the missing info. In any case, I agree that this is a good tool to keep in mind. --Gregg