Comments on Programming Scala

Comment on 'Traversing, Mapping, Filtering, Folding, and Reducing'

2009-08-11T08:20:02-07:00

Traversing, Mapping, Filtering, Folding, and Reducing

It returns List(<1>, <2>, <3>, <4>, <5>, <6>). Note that we had to call reverse on the result to get back a list in the same order as the input list.

I think it would help to add a comment stating why you do (list, x) => ("<" + x + ">") :: list instead of (list, x) => list :: ("<" + x + ">")

since the second option would remove the need for "reverse" - is this to "add to head" and get O(2 * n) - also reverse - instead of add to tail and get O(sqr(n))/2 ?

by the way - i am enjoying your book a lot
— shalomDeitch (2009-08-11 08:20:02)

Comment on 'Currying'

2009-07-25T21:20:18-07:00

Currying

We’ll revisit the curry method in the section called “Function Types” in Chapter 12, The Scala Type System.

While we did see the Function.curried method, we didn't see the curry method above.
— jrduncans (2009-07-25 21:20:18)

Comment on 'Recap: Functional Component Abstractions'

2009-07-18T19:45:02-07:00

Recap: Functional Component Abstractions

HTTP is another good example. With a handful of message types and a very simple standard for message content, it set the stage for the Internet revolution. RESTful web services built on top of HTTP are also proving successful as components, but they are just complex enough that care is required to ensure that they work successfully.

"... required to ensure that they work successfully."
— chrislewis (2009-07-18 19:45:02)

Comment on 'Tail Calls and Tail-Call Optimization'

2009-07-18T11:14:06-07:00

Tail Calls and Tail-Call Optimization

This script produces the same output as before. Now, factorial does all the work with a nested method, fact, that is tail recursive because it passes an accumulator argument to hold the computation in progress. This argument is computed with a multiplication before the recursive call to fact, which is now the very last thing that is done. In our previous implementation, this multiplication was done after the call to fact. When we call fact(1), we simply return the accumulated value.

Same as previous code sample: why not if or case with literal?
— hotdog (2009-07-18 11:14:06)

Comment on 'Recursion'

2009-07-18T11:12:58-07:00

Recursion

The output is the same, but now there are no mutable variables. Recursion not only helps us avoid mutable variables, it is also the most natural way to express some functions, particularly mathematical functions. The recursive definition in our second factorial is structurally similar to a definition for factorials that you might see in a mathematics book.

What's the point of pattern matching here? I think it's supposed to make branches easier to read... if (i==1) 1 else i*factorial(i-1) looks much easier to comprehend, isn't it?

If you insist on match, what's wrong with case 1 => 1? Current version looks like a test question :)
— hotdog (2009-07-18 11:12:58)

Comment on 'Traversing, Mapping, Filtering, Folding, and Reducing'

2009-07-12T21:52:10-07:00

Traversing, Mapping, Filtering, Folding, and Reducing

This script produces the following output:

Thanks. Obsolete "output". will fix.
— deanwampler (2009-07-12 21:52:10)

Comment on 'Traversing, Mapping, Filtering, Folding, and Reducing'

2009-07-09T12:29:38-07:00

Traversing, Mapping, Filtering, Folding, and Reducing

This script produces the following output:

"This script produces the output ArrayBufferAlabama."

No, I don't think it does :-)

(It produces something like ArrayBuffer((Alabama,10), (Alaska,6) ... )
— NikolajLindberg (2009-07-09 12:29:38)

Comment on 'Implicits'

2009-06-24T21:08:45-07:00

Implicits

We can’t modify RichString or Predef to add an implicit conversion method for our custom FancyString class. Instead, we define an object named FancyString2RichString and define the conversion method in it. We then import the contents of this object and the converter gets invoked implicitly in the last line. The output of this script is the following.

Since the original example above is for adding methods, I think it makes sense to show that as the first example of implicit conversions. For example, give FancyString a method that doesn't exist in RichString like returning a crc32 of it.
— stevej (2009-06-24 21:08:45)