Am Mittwoch 17 Juni 2009 01:41:01 schrieb George Huber:
Hi,
This is more of a philosophical question then anything else.
Recently I posted a question (see " exercise 3.10 in YAHT") and now Rolle is encountering what appears to be the same error (see "hci reports "The last statement in a 'do' construct must be an expression" error"). In both cases the responses have been something on the order of "must be the indentation".
So...my questions are:
(1) what was the driving force behind using white-space to denote code blocks? From a beginners perspective (especially coming from a strong C / C++ background) this seems to add to the learning curve for the language, and can add a good deal of frustration.
Readability. Properly indented code is far easier to read, braces and semicolons are then only clutter.
(2) I know using layout is optional -- we can curly braces and semicolons (not sure what this method is called correctly), but in the books and sources that I have looked at this seems to be mentioned in passing, so I'm guessing "good haskell format" is to use layout. And if this is true, is there any reason for this? better performance? easier parsing?
It's only easier to parse for humans, it's harder to write a parser for the layout rule. But humans are considered more important.
(3) Finally, is there a book or online reference that uses curly braces and semicolons from the start -- maybe introducing the concept of layout after all the language syntax is firmly grounded?
I know none.
George.
PS -- For those of you that answered my first post, I sort-of solved my problem. From your conviction that there was not an error in the function (even though this is where the compiler was claiming it to be), I moved stuff around in the source file while not touching the function itself and the error disappeared. Not a satisfactory solution I know, but for now it will do till I get the syntax of Haskell down. Thanks for everyone's help.
Read http://haskell.org/onlinereport/lexemes.html#sect2.7 and http://haskell.org/onlinereport/syntax-iso.html#sect9.3 for an explanation of the layout rule.
George