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Vincenzo Maggio
Vincenzo Maggio

Reputation: 3869

Is 'yield' in Scala equivalent to map function?

I'm starting to study the Scala programming language. I've some grasp of FP languages like Erlang and Haskell and I have a doubt about the meaning of the for/yield expression, like:

for (arg <- args) yield arg.length

This would collect an array with the lengths of any input argument. From what I've understood this seems like the map function in normal FP programming:

map (\a -> a * 2) [1, 2, 3] (in Haskell)

I know that Scala library contains the scala.collection.map method, so I would like to know: is there any difference or limitation in using either style, or they are exactly the same?

Upvotes: 7

Views: 2054

Answers (3)

tenshi
tenshi

Reputation: 26576

for ... yield comprehension in Scala is translated by compiler to the map, flatMap and withFilter method calls. for without yield would be translated to the foreach method call. You can find some examples and more information here:

http://tataryn.net/2011/10/whats-in-a-scala-for-comprehension/

and here

http://adamwojtuniak.wordpress.com/2010/09/24/scala-for-comprehensions/

Upvotes: 15

adelbertc
adelbertc

Reputation: 7320

The for-yield is compiled down to maps - it is in the Programming in Scala book.

Upvotes: 3

Ptharien&#39;s Flame
Ptharien&#39;s Flame

Reputation: 3246

Scala's for/yield expressions are completely equivalent to list/monad comprehensions in Haskell, and have exactly the same capabilities, as long as you stick to one type per for expression. (I don't know about Erlang, though.)

In particular, your example exactly translates to [length arg | arg <- args], translating the Scala method call x.f to the Haskell function application f x.

Upvotes: 6

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