Getting the desugared part of a Scala for/comprehension expression?

Does anyone know how to get the (Scala part only) desugared translation of a for/comprehension expression before it actually tries to compile in the REPL (or compiler)?

The only thing I've found so far is the compiler "-print" flag but that gives you the full Scala translation…

Solution 1:

As I already said in the other topic, scalac -print prints out scala code, not java. It translates all scala keywords that are not directly compatible with java to normal scala code. It is not possible to let the compiler translate only parts afaik. But basically a for-comprehension is always translated the same way.

A simple for/yield like this

for(x <- List(1,2,3)) yield x*x

will be translated to

List(1,2,3).map {x => x*x}

And without yield

for(x <- List(1,2,3)) println(x)

to

List(1,2,3).foreach{x => println(x)}

Nested fors will be translated to nested flatMap/map constructs

for(x <- List(1,2,3); y <- List(4,5,6)) yield x*y

will be translated to

List(1,2,3).flatMap { x =>
  List(4,5,6).map { y =>
    x*y
  }
}

So there is absolutely no magic

Solution 2:

It doesn't seem to exists any possibilities to desugar "for/comprehension" expressions directly within the REPL. But as an alternative one can use some Scala compiler options like "-print" or for simple expressions "Xprint:typer -e"

Example:

To get the desugard output from a file use the "-print" flag:

# scala -print file.scala

To desugar a simple one-liner expression, use the "-Xprint:typer -e" flag:

# scala -Xprint:typer -e "for (i <- 0 to 100) yield i"