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…
Scala offers a lightweight notation for expressing sequence comprehensions. Comprehensions have the form for (enumerators) yield e , where enumerators refers to a semicolon-separated list of enumerators. An enumerator is either a generator which introduces new variables, or it is a filter.
Scala Language For Expressions Desugaring For Comprehensions for comprehensions in Scala are just syntactic sugar. These comprehensions are implemented using the withFilter , foreach , flatMap and map methods of their subject types.
Comprehensions is a construct in Scala which allows us to evaluate certain expressions. The For Comprehension has the form for (enumerators) yield e , where enumerators refer to a semi-colon separated list of enumerators. An enumerator can either be a generator that iterates the list or a filter.
Finally, we discovered that a for-comprehension is just syntactic sugar for a sequence of calls to methods foreach, map, flatMap, and withFilter.
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
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