Michael Maloney <amaloney at earthlink.net> wrote:
> Well, all the books have said to start small, so . . .

Exactly! After all - it is SMALLtalk. :-)

> In case anyone else finds it useful, here is a method I've added
> to Fraction.
> 
> "(5/3) printStringAsMixedNumber" prints as 1(2/3).
> 
> The newbie part is: Have I followed accepted practice
> as far as naming convention and putting the method in
> the printing protocol?

Think so. I might have named it #printAsMixedNumber, but that is mere
taste.

> Also, (especially) since I modified a kernal class, should I
> have named it something else?

Nope, seems fine to me. A few advice:

1. Learn to use changesets instead of .st files. They are a bit more
useful.

2. When adding "printYaddaYadda" methods I usually tend to prefer the
form that takes a stream as an argument (as #printOn:) - it can make the
method a bit more useful. More on that below.

3. Your line that goes:
	text _ '' , wholePart printString , fractionPart printString.
...can instead be written as:
	text _ wholePart printString , fractionPart printString.
There is no need to concatenate with an empty String at the beginning. I
am not sure why you did that.

Ok, follow me on a little "excursion" here - this is not meant as
criticism - hopefully there is something to be learned from it. Let's
change the method a teeny bit first:

printStringAsMixedNumber
	| wholePart fractionPart |
	wholePart _ self truncated.
	fractionPart _ self - wholePart.
	^wholePart printString , fractionPart printString

The return is always "evaluated" last so you can always safely put it at
the beginning of the line and you don't have to use parentheses. You
also don't need to end the final statement in the method with the
.-character. It is a "statement separator" not a "statement endmarker".
On the other hand it can be there without errors. 

Let's go a bit further:
printStringAsMixedNumber
	| wholePart |
	wholePart _ self truncated.
	^wholePart printString , (self - wholePart) printString

When examining the implementation of #printString (select it and press
Alt-m) we see that it is actually a "limited" version. In this case
perhaps #fullPrintString would be better - at least we get rid of two
extra message sends! :-) (Yeah, yeah, permature optimization is the root
of all evil which Donald Knuth didn't say btw).

So currently we have:
printStringAsMixedNumber
	| wholePart |
	wholePart _ self truncated.
	^wholePart fullPrintString , (self - wholePart) fullPrintString

...if we then take a look at fullPrintString (Alt-m) we find it
implemented like this:
^String streamContents: [:s | self printOn: s]

The method streamContents: is kind of new in Smalltalk I think. I just
checked the versions of it (Alt-v) but I found no reference to when it
was introduced. It is a nice method though and makes it easy to produce
a String by using methods that wants to write on a stream.

Hmmm. So then we might end up with my suggestion for a stream-based
implementation like this:
printAsMixedNumberOn: aStream	
	| wholePart |
	wholePart _ self truncated.
	wholePart printOn: aStream.
	(self - wholePart) printOn: aStream

This method takes a Stream as an argument and writes the representation
on the stream. The nice part with this is that the Stream can be any
kind of Stream like for example a FileStream.

...and if you still want a method returning a String you can always add
an extra method like this:
printStringAsMixedNumber
	^String streamContents: [:stream | self printAsMixedNumberOn: stream]


And here ends my little excursion. :-)

> Cheers,
> Mike

Cheers, Göran