Re: Another Error
Derek Parnell wrote:
> Rich Klender wrote:
> > Well, I hit another snag, if anyone would be gracious enough to help!!!
> >
> > Here's the code:
>
> I've reduced it to the problem area ...
>
> > sequence Correct
> > if Correct = 'y' or Correct = 'Y' then
>
> > true/false condition must be an ATOM
>
> This has been one of my few disappointments with Euphoria. Robert Craig, the
> creator of the language, has defined the 'if' statement in a manner which most
> other languages do not.
Which languages are you including in your list of
"most other languages"? I know Basic works the way you would like,
but C/C++ (a more popular language) does not. People who come to
Euphoria from a Basic background are often confused by this,
but many other people, such as myself, who are used to C/C++,
think it's fine to require a function call to compare strings or
arrays in this way. This is not something that Robert Craig invented,
all on his own, just to annoy the rest of the world.
> Bear with me please, as I understand that this is your
> first real programming effort - I may get a little technical here 
>
> Euphoria defines the IF statement as
>
> IF :: 'if' ATOMEXPRESSION 'then'
> [ STATEMENTBLOCK ]
> [ ELSEPHRASE ]
> 'end if'
>
> but most other languages define it as
>
> IF :: 'if' COMPARISIONEXPRESSION 'then'
> [ STATEMENTBLOCK ]
> [ ELSEPHRASE ]
> 'end if'
>
> The difference is that Euphoria evaluates the expression that follows the 'if'
> keyword in a manner that is not expected by nearly everyone else except
> Robert.
> Taking your example code, this is what happens...
>
> if Correct = 'y' or Correct = 'Y' then
>
> Let's assume that the user entered "Y" into the variable Correct. Euphoria
> will
> first evaluate
>
> "Y" = 'y'
>
> which is a sequence operation, meaning for each element in the sequence it
> will
> apply the " = 'y' " fragment. Remember that strings are sequences so the
> value
> in Correct is equivalent to
>
> {'Y'}
>
> so the result of this first sequence operation is
> {'Y'} = 'y' ===> {0}
> because the operation compares each element in Correct with 'y' and replaces
> the result with either 1 or 0 depending on the comparision result. 1 means
> true
> and 0 means false.
>
> The second sequence operation is
>
> Correct = 'Y'
>
> which is the same as
>
> {'Y'} = 'Y'
>
> which results in {1}
>
> The final sequence operation is then
> {0} or {1}
> which results in {1}
>
> The net result of this is that your IF statement is equivalent to
>
> if {1} then
>
> but this is wrong as Euphoria requires the expression to result in an atom
> value
> and not a sequence. This is why Euphoria doesn't like things like
>
> if "yes" then
>
> But back to most other languages...
>
> if Correct = 'y' or Correct = 'Y' then
>
> they would evaluate the expression as a comparision instead.
>
> Correct = 'y' ===> false
> Correct = 'Y' ===> true
> false or true ===> true
>
> and thus your statement is equivalent to
>
> if true then
>
> which makes a lot more common sense than Robert's concept of an IF statement.
>
>
> However, as Robert's philosophy on this is never going to change,
Yeah, I guess I'm just a stubborn old fool. 
> the only safe
> way to code equality tests in IF statements in Euphoria is this ...
>
> if equal(Correct, 'y') or equal(Correct, 'Y') then
>
> which is not an intuitive alternative.
I assume you meant:
if equal(Correct, "y") or equal(Correct, "Y") then
Anyway, thanks for the tutorial. I know there are newbies
who are confused by this feature.
For what it's worth, I'd probably code it as:
if find('Y', upper(Correct)) then ...
which will allow the user to type any of:
Y
y
yes
Yes
YES
yeah
etc.
rather than insisting that he type precisely "y" or "Y"
(with no extra characters, leading or trailing blanks etc.).
Or perhaps something like:
if find(upper(Correct), {"Y", "YES", "OK", "OUI", "JA", "SI"}) then
Regards,
Rob Craig
Rapid Deployment Software
http://www.RapidEuphoria.com
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