blocks|key|394939|text|正如我在另一个主题中所说的，scalac+-print打印的是scala代码，而不是java。它将所有与java不直接兼容的scala关键字转换为普通的scala代码。不可能让编译器只翻译部分afaik。但从根本上讲，for-comprehension总是以同样的方式被翻译。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|394940|像这样的简单的for/yield|394941|for(x+<-+List(1,2,3))+yield+x*x|code-block|syntax|javascript|394942|将被翻译为|394943|List(1,2,3).map+{x+=>+x*x}|394944|而且没有让步|394945|for(x+<-+List(1,2,3))+println(x)|394946|至|394947|List(1,2,3).foreach{x+=>+println(x)}|394948|嵌套的fors将转换为嵌套的flatMap/map构造|394949|for(x+<-+List(1,2,3);+y+<-+List(4,5,6))+yield+x*y|394950|394951|List(1,2,3).flatMap+{+x+=>
++List(4,5,6).map+{+y+=>
++++x*y
++}
}|394952|所以绝对没有魔法|394953|entityMap^0|E|D|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1C|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1D|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1E|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1F|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1G|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1H|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1I|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1J|8|@]|D|@]|E|$K|L]]|$1|Y|3|Z|5|6|7|1K|8|@]|D|@]|E|$]]|$1|10|3|11|5|J|7|1L|8|@]|D|@]|E|$K|L]]|$1|12|3|N|5|6|7|1M|8|@]|D|@]|E|$]]|$1|13|3|14|5|J|7|1N|8|@]|D|@]|E|$K|L]]|$1|15|3|16|5|6|7|1O|8|@]|D|@]|E|$]]|$1|17|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|18|$]]

As I already said in the other topic, <code>scalac -print</code> 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

<pre><code>for(x &lt;- List(1,2,3)) yield x*x
</code></pre>

will be translated to

<pre><code>List(1,2,3).map {x =&gt; x*x}
</code></pre>

And without yield

<pre><code>for(x &lt;- List(1,2,3)) println(x)
</code></pre>

to

<pre><code>List(1,2,3).foreach{x =&gt; println(x)}
</code></pre>

Nested fors will be translated to nested flatMap/map constructs

<pre><code>for(x &lt;- List(1,2,3); y &lt;- List(4,5,6)) yield x*y
</code></pre>

will be translated to

<pre><code>List(1,2,3).flatMap { x =&gt;
 List(4,5,6).map { y =&gt;
 x*y
 }
}
</code></pre>

So there is absolutely no magic

blocks|key|611046|text|在REPL中，似乎不存在直接对"for/comprehension“表达式进行去糖化的可能性。但作为替代，可以使用一些Scala编译器选项，如"-print“或用于简单表达式"Xprint:typer+-e”|type|unstyled|depth|inlineStyleRanges|entityRanges|data|611047|示例：|611048|要从文件中获取desugard输出，请使用"-print“标志：|611049|#+scala+-print+file.scala|code-block|syntax|javascript|611050|要去掉一个简单的单行表达式，请使用"-Xprint:typer+-e“标志：|611051|#+scala+-Xprint:typer+-e+"for+(i+<-+0+to+100)+yield+i"|611052|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|T|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

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:

<pre><code># scala -print file.scala
</code></pre>

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

<pre><code># scala -Xprint:typer -e "for (i &lt;- 0 to 100) yield i"
</code></pre>

blocks|key|395036|text|要查看简单去图形化后的结果，请使用-Xprint:parser选项。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|395037|如果您有一个名为test.scala的简单输入文件|395038|object+Test+{
++for(x+<-+List(1,2,3);+y+<-+List(4,5,6))+yield+x*y
}|code-block|syntax|javascript|395039|然后使用scalac+-Xprint:parser对其进行编译，输出如下：|395040|$+scalac+-Xprint:parser+test.scala+
[[syntax+trees+at+end+of++++++++++++++++++++parser]]+//+test.scala
package+<empty>+{
++object+Test+extends+scala.AnyRef+{
++++def+<init>()+=+{
++++++super.<init>();
++++++()
++++};
++++List(1,+2,+3).flatMap(((x)+=>+List(4,+5,+6).map(((y)+=>+x.$times(y)))))
++}
}|395041|要获得适用于-Xprint:<phase>的编译器阶段的完整列表，请执行以下操作：|395042|$+scalac+-Xshow-phases
+++++++++++++phase+name++id++description
+++++++++++++----------++--++-----------
+++++++++++++++++parser+++1++parse+source+into+ASTs,+perform+simple+desugaring
++++++++++++++++++namer+++2++resolve+names,+attach+symbols+to+named+trees
+++++++++packageobjects+++3++load+package+objects
++++++++++++++++++typer+++4++the+meat+and+potatoes:+type+the+trees
+++++++++++++++++patmat+++5++translate+match+expressions
+++++++++superaccessors+++6++add+super+accessors+in+traits+and+nested+classes
+++++++++++++extmethods+++7++add+extension+methods+for+inline+classes
++++++++++++++++pickler+++8++serialize+symbol+tables
++++++++++++++refchecks+++9++reference/override+checking,+translate+nested+objects
+++++++++++selectiveanf++10++
+++++++++++selectivecps++11++
++++++++++++++++uncurry++12++uncurry,+translate+function+values+to+anonymous+classes
++++++++++++++tailcalls++13++replace+tail+calls+by+jumps
+++++++++++++specialize++14++@specialized-driven+class+and+method+specialization
++++++++++explicitouter++15++this+refs+to+outer+pointers,+translate+patterns
++++++++++++++++erasure++16++erase+types,+add+interfaces+for+traits
++++++++++++posterasure++17++clean+up+erased+inline+classes
+++++++++++++++lazyvals++18++allocate+bitmaps,+translate+lazy+vals+into+lazified+defs
+++++++++++++lambdalift++19++move+nested+functions+to+top+level
+++++++++++constructors++20++move+field+definitions+into+constructors
++++++++++++++++flatten++21++eliminate+inner+classes
++++++++++++++++++mixin++22++mixin+composition
++++++++++++++++cleanup++23++platform-specific+cleanups,+generate+reflective+calls
++++++++++++++++++icode++24++generate+portable+intermediate+code
++++++++++++++++inliner++25++optimization:+do+inlining
inlineExceptionHandlers++26++optimization:+inline+exception+handlers
+++++++++++++++closelim++27++optimization:+eliminate+uncalled+closures
++++++++++++++++++++dce++28++optimization:+eliminate+dead+code
++++++++++++++++++++jvm++29++generate+JVM+bytecode
+++++++++++++++terminal++30++The+last+phase+in+the+compiler+chain|395043|-Xprint:<phase>选项也适用于scala，因此也适用于REPL。但是，您还将看到REPL插入的所有包装器代码。|395044|$+scala+-Xprint:parser
Welcome+to+Scala+version+2.10.3+(Java+HotSpot(TM)+64-Bit+Server+VM,+Java+1.7.0_25).
Type+in+expressions+to+have+them+evaluated.
Type+:help+for+more+information.

<..a+lot+of+initialisation+code+printed..>

scala>+object+Test+{
+++++%7C+++for(x+<-+List(1,2,3);+y+<-+List(4,5,6))+yield+x*y
+++++%7C+}
[[syntax+trees+at+end+of++++++++++++++++++++parser]]+//+<console>
package+$line3+{
++object+$read+extends+scala.AnyRef+{
++++def+<init>()+=+{
++++++super.<init>();
++++++()
++++};
++++object+$iw+extends+scala.AnyRef+{
++++++def+<init>()+=+{
++++++++super.<init>();
++++++++()
++++++};
++++++object+$iw+extends+scala.AnyRef+{
++++++++def+<init>()+=+{
++++++++++super.<init>();
++++++++++()
++++++++};
++++++++object+Test+extends+scala.AnyRef+{
++++++++++def+<init>()+=+{
++++++++++++super.<init>();
++++++++++++()
++++++++++};
++++++++++List(1,+2,+3).flatMap(((x)+=>+List(4,+5,+6).map(((y)+=>+x.$times(y)))))
++++++++}
++++++}
++++}
++}
}

[[syntax+trees+at+end+of++++++++++++++++++++parser]]+//+<console>
package+$line3+{
++object+$eval+extends+scala.AnyRef+{
++++def+<init>()+=+{
++++++super.<init>();
++++++()
++++};
++++lazy+val+$result+=+$line3.$read.$iw.$iw.Test;
++++val+$print:+String+=+{
++++++$read.$iw.$iw;
++++++"".$plus("defined+module+").$plus("Test").$plus("\n")
++++}
++}
}

defined+module+Test

scala>+|395045|entityMap^0|H|E|0|8|A|0|0|4|L|0|0|6|F|0|0|0|F|L|5|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|16|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1E|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|W|3|X|5|J|7|1K|8|@]|D|@]|E|$K|L]]|$1|Y|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Z|$]]

To see the result after simple desugaring use the <code>-Xprint:parser</code> option.

If you have this simple input file named <code>test.scala</code>:

<pre><code>object Test {
 for(x &lt;- List(1,2,3); y &lt;- List(4,5,6)) yield x*y
}
</code></pre>

Then compiling it using <code>scalac -Xprint:parser</code> prints out:

<pre><code>$ scalac -Xprint:parser test.scala 
[[syntax trees at end of parser]] // test.scala
package &lt;empty&gt; {
 object Test extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 List(1, 2, 3).flatMap(((x) =&gt; List(4, 5, 6).map(((y) =&gt; x.$times(y)))))
 }
}
</code></pre>

To get a complete list of compiler phases applicable to <code>-Xprint:&lt;phase&gt;</code> do this:

<pre><code>$ scalac -Xshow-phases
 phase name id description
 ---------- -- -----------
 parser 1 parse source into ASTs, perform simple desugaring
 namer 2 resolve names, attach symbols to named trees
 packageobjects 3 load package objects
 typer 4 the meat and potatoes: type the trees
 patmat 5 translate match expressions
 superaccessors 6 add super accessors in traits and nested classes
 extmethods 7 add extension methods for inline classes
 pickler 8 serialize symbol tables
 refchecks 9 reference/override checking, translate nested objects
 selectiveanf 10 
 selectivecps 11 
 uncurry 12 uncurry, translate function values to anonymous classes
 tailcalls 13 replace tail calls by jumps
 specialize 14 @specialized-driven class and method specialization
 explicitouter 15 this refs to outer pointers, translate patterns
 erasure 16 erase types, add interfaces for traits
 posterasure 17 clean up erased inline classes
 lazyvals 18 allocate bitmaps, translate lazy vals into lazified defs
 lambdalift 19 move nested functions to top level
 constructors 20 move field definitions into constructors
 flatten 21 eliminate inner classes
 mixin 22 mixin composition
 cleanup 23 platform-specific cleanups, generate reflective calls
 icode 24 generate portable intermediate code
 inliner 25 optimization: do inlining
inlineExceptionHandlers 26 optimization: inline exception handlers
 closelim 27 optimization: eliminate uncalled closures
 dce 28 optimization: eliminate dead code
 jvm 29 generate JVM bytecode
 terminal 30 The last phase in the compiler chain
</code></pre>

The <code>-Xprint:&lt;phase&gt;</code> option is also applicable to <code>scala</code> and thus to the REPL. However, you will see all the wrapper code the REPL inserts as well.

<pre><code>$ scala -Xprint:parser
Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_25).
Type in expressions to have them evaluated.
Type :help for more information.

&lt;..a lot of initialisation code printed..&gt;

scala&gt; object Test {
 | for(x &lt;- List(1,2,3); y &lt;- List(4,5,6)) yield x*y
 | }
[[syntax trees at end of parser]] // &lt;console&gt;
package $line3 {
 object $read extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 object $iw extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 object $iw extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 object Test extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 List(1, 2, 3).flatMap(((x) =&gt; List(4, 5, 6).map(((y) =&gt; x.$times(y)))))
 }
 }
 }
 }
}

[[syntax trees at end of parser]] // &lt;console&gt;
package $line3 {
 object $eval extends scala.AnyRef {
 def &lt;init&gt;() = {
 super.&lt;init&gt;();
 ()
 };
 lazy val $result = $line3.$read.$iw.$iw.Test;
 val $print: String = {
 $read.$iw.$iw;
 "".$plus("defined module ").$plus("Test").$plus("\n")
 }
 }
}

defined module Test

scala&gt; 
</code></pre>

blocks|key|395068|text|宏怎么样？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|395069|import+scala.reflect.macros.Context
import+scala.reflect.runtime.universe._
import+scala.language.experimental.macros

def+_desugar(c+:+Context)(expr+:+c.Expr[Any]):+c.Expr[Unit]+=+{
++import+c.universe._
++println(show(expr.tree))
++reify+{}
}

def+desugar(expr+:+Any)+=+macro+_desugar|code-block|syntax|javascript|395070|根据您的请求，可以直接在REPL中使用：|395071|scala>+desugar+{+for(i+<-+List(1,2,3,4,5))+yield+i+}
immutable.this.List.apply[Int](1,+2,+3,+4,+5).map[Int,+Any](((i:+Int)+=>
i))(immutable.this.List.canBuildFrom[Int])

scala>+desguar+{+for(i+<-+(0+to+10)+if+(i+>+5))+yield+i+}
scala.this.Predef.intWrapper(0).to(10).withFilter(((i:+Int)+=>+i.>(5))).map[Int,
Any](((i:+Int)+=>+i))(immutable.this.IndexedSeq.canBuildFrom[Int])|395072|它也适用于其他任意表达式。|395073|scala>+desugar+{
+++++%7C+++val+x+=+20
+++++%7C+++val+y+=+10
+++++%7C+++println(x+%2B+y)
+++++%7C+}
{
++val+x:+Int+=+20;
++val+y:+Int+=+10;
++scala.this.Predef.println(x.%2B(y))
}|395074|这可能是您在任何时候都不需要编译数据或将数据转储到文件中就能得到的最接近的结果。可以直接在REPL中定义宏，也可以在使用:load命令加载的外部文件中定义宏。|offset|length|style|CODE|395075|entityMap^0|0|0|0|0|0|0|1O|5|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|12|8|@$Q|13|R|14|S|T]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

How about a macro?

<pre><code>import scala.reflect.macros.Context
import scala.reflect.runtime.universe._
import scala.language.experimental.macros

def _desugar(c : Context)(expr : c.Expr[Any]): c.Expr[Unit] = {
 import c.universe._
 println(show(expr.tree))
 reify {}
}

def desugar(expr : Any) = macro _desugar
</code></pre>

This can be used directly in the REPL, as per your request:

<pre><code>scala&gt; desugar { for(i &lt;- List(1,2,3,4,5)) yield i }
immutable.this.List.apply[Int](1, 2, 3, 4, 5).map[Int, Any](((i: Int) =&gt;
i))(immutable.this.List.canBuildFrom[Int])

scala&gt; desguar { for(i &lt;- (0 to 10) if (i &gt; 5)) yield i }
scala.this.Predef.intWrapper(0).to(10).withFilter(((i: Int) =&gt; i.&gt;(5))).map[Int,
Any](((i: Int) =&gt; i))(immutable.this.IndexedSeq.canBuildFrom[Int])
</code></pre>

It also works on other arbitrary expressions.

<pre><code>scala&gt; desugar {
 | val x = 20
 | val y = 10
 | println(x + y)
 | }
{
 val x: Int = 20;
 val y: Int = 10;
 scala.this.Predef.println(x.+(y))
}
</code></pre>

This is probably the closest you'll get to what you're asking without ever having to compile or dump the data out to a file at any point. You can define the macro directly in the REPL, or in an external file loaded with the <code>:load</code> command.

blocks|key|611130|text|在Scala2.11中，也可以使用quasiquotes|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|611131|val+universe:+scala.reflect.runtime.universe.type+=+scala.reflect.runtime.universe
import+universe._
val+tree+=+q"""
++val+x+=+20
++val+y+=+10
++println(x+%2B+y)
"""
println(tree)|code-block|syntax|javascript|611132|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.scala-lang.org/overviews/quasiquotes/intro.html^0|H|B|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

In scala 2.11, it is also possible to use <a href="http://docs.scala-lang.org/overviews/quasiquotes/intro.html" rel="nofollow">quasiquotes</a>:

<pre><code>val universe: scala.reflect.runtime.universe.type = scala.reflect.runtime.universe
import universe._
val tree = q"""
 val x = 20
 val y = 10
 println(x + y)
"""
println(tree)
</code></pre>

blocks|key|611205|text|Intellij有一个名为"Explain+Scala“的功能，它可以做很多去糖化的工作，包括直接在你正在编辑的文件中将理解扩展到地图/扁平地图/过滤器中。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|611206|请注意，从IntelliJ+2017.1开始，这个代码现在被称为"Desugar+Scala+Code“，并且位于"Code”菜单中(感谢Mikaël提供的信息)。|611207|​|611208|📷|atomic|611209|611210|entityMap|0|LINK|mutability|MUTABLE|url|https://twitter.com/pivovarit/status/798923522311528448|1|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/27b41eb7f6e40253ebd5992d1b85eced.png|imageAlt^0|E|D|0|0|0|0|0|1|1|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|D|3|E|5|6|7|13|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|14|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|K|3|G|5|6|7|19|8|@]|9|@]|C|$]]|$1|L|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|M|$N|$5|O|P|Q|C|$R|S]]|T|$5|U|P|V|C|$W|X|Y|-4]]]]

Intellij has a feature called "<a href="https://twitter.com/pivovarit/status/798923522311528448" rel="noreferrer">Explain Scala</a>" that does a LOT of desugaring including expanding for comprehensions into map/flatMap/filter directly in the file you are editing.

Please note that since IntelliJ 2017.1 this is now called "Desugar Scala Code" and is in the "Code" menu (thanks Mikaël for the info).

<a href="https://i.stack.imgur.com/r2fAR.png" rel="noreferrer"><img src="https://i.stack.imgur.com/r2fAR.png" alt="IntelliJ Desugar Scala"></a>

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…

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

编译器

Java

有谁知道如何在实际尝试在REPL (或编译器)中编译一个for/compiler表达式之前获得(仅限Scala部分)去糖化的翻译？到目前为止，我发现的唯一一件事就是编译器"-print“标志，但它给出了完整的Scala转换…

问获取Scala for/comprehension表达式的去糖化部分？
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问获取Scala for/comprehension表达式的去糖化部分？
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