Why would a 'for' require a definition of 'map'?

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Your code is expanded to:

Lit("a").findAllMatchesIn("aabbaba").map(m => m.group(0))

A more thorough explanation about lifting into a monad might help, but
it might not, so I won't.

Kenneth McDonald wrote:
> Here's the error message:
>
> MBP:scalaapplication1 Ken$ scalac rex.scala
> rex.scala:265: error: value map is not a member of
> rex.MatchResultIterator
> val sequence = for(m <-
> Lit("a").findAllMatchesIn("aabbaba")) yield m.group(0)
>
> and here is the definition of MatchResultIterator:
>
> class MatchResultIterator(val matches:Iterator[Regex.Match], val
> matcher:Matcher) {
> var lastEnd = 0
> def hasNext = matches.hasNext
> def next = matches.next
> }
>
> I'm probably just being obtuse, but I can't see the need for a 'map'
> definition here.
>
> Thanks,
> Ken
>
>
>

- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

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Kenneth McDonald schrieb:
> I'm probably just being obtuse, but I can't see the need for a 'map'
> definition here.

Because for is defined that way. To use for, you must implement
map, flatMap and filter. In scala for is not a loop, but a
comprehension: http://www.scala-lang.org/node/111

- Florian.

Florian Hars wrote:
> Kenneth McDonald schrieb:
>> I'm probably just being obtuse, but I can't see the need for a 'map'
>> definition here.
>
> Because for is defined that way. To use for, you must implement
> map, flatMap and filter. In scala for is not a loop, but a
> comprehension: http://www.scala-lang.org/node/111

Note you won't need to explicitly implement map, filter, flatMap,
foreach if your iterator inherits from Iterator. You've already
implemented its only abstract methods (hasNext, next).

Perhaps it's java.util.Iterator and not scala.Iterator?

On Sun, Jan 25, 2009 at 4:44 AM, Eric Willigers <ewilligers@gmail.com> wrote:

Florian Hars wrote:

Kenneth McDonald schrieb:

I'm probably just being obtuse, but I can't see the need for a 'map' definition here.

Because for is defined that way. To use for, you must implement
map, flatMap and filter. In scala for is not a loop, but a comprehension: http://www.scala-lang.org/node/111

Note you won't need to explicitly implement map, filter, flatMap, foreach if your iterator inherits from Iterator. You've already implemented its only abstract methods (hasNext, next).

--
Viktor Klang
Senior Systems Analyst

Viktor Klang schrieb:
> Perhaps it's java.util.Iterator and not scala.Iterator?

He just called his class SomethingIterator without extending anything,
so he didn't inherit any methods. In effect, all that's missing is an
"extends Iterator" in his class definition.

- Florian

Haha,

marvellous,

That's what I get for wrongly assuming the most basic stuff is already present. ;D


On Sun, Jan 25, 2009 at 10:02 AM, Florian Hars <hars@bik-gmbh.de> wrote:

Viktor Klang schrieb:

Perhaps it's java.util.Iterator and not scala.Iterator?

He just called his class SomethingIterator without extending anything,
so he didn't inherit any methods. In effect, all that's missing is an "extends Iterator" in his class definition.

- Florian

--
Viktor Klang
Senior Systems Analyst