diff options
| -rw-r--r-- | src/dotty/tools/dotc/parsing/Parsers.scala | 2 | ||||
| -rw-r--r-- | src/dotty/tools/dotc/reporting/diagnostic/messages.scala | 32 |
2 files changed, 33 insertions, 1 deletions
diff --git a/src/dotty/tools/dotc/parsing/Parsers.scala b/src/dotty/tools/dotc/parsing/Parsers.scala index 6adb7f010..8fc99f072 100644 --- a/src/dotty/tools/dotc/parsing/Parsers.scala +++ b/src/dotty/tools/dotc/parsing/Parsers.scala @@ -1327,7 +1327,7 @@ object Parsers { if (in.token == YIELD) { in.nextToken(); ForYield(enums, expr()) } else if (in.token == DO) { in.nextToken(); ForDo(enums, expr()) } else { - if (!wrappedEnums) syntaxErrorOrIncomplete("`yield' or `do' expected") + if (!wrappedEnums) syntaxErrorOrIncomplete(YieldOrDoExpectedInForComprehension()) ForDo(enums, expr()) } } diff --git a/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/src/dotty/tools/dotc/reporting/diagnostic/messages.scala index c4e84aaee..303ab0437 100644 --- a/src/dotty/tools/dotc/reporting/diagnostic/messages.scala +++ b/src/dotty/tools/dotc/reporting/diagnostic/messages.scala @@ -512,4 +512,36 @@ object messages { |}""".stripMargin } + case class YieldOrDoExpectedInForComprehension()(implicit ctx: Context) extends Message(19) { + val kind = "Syntax" + val msg = hl"${"yield"} or ${"do"} expected" + + val explanation = + hl"""When the enumerators in a for comprehension are not placed in parentheses or + |braces, a ${"do"} or ${"yield"} statement is required after the enumerators section + |of the comprehension. + | + |You can save some keystrokes by omitting the parentheses and writing + | + |${"val numbers = for i <- 1 to 3 yield i"} + | + | instead of + | + |${"val numbers = for (i <- 1 to 3) yield i"} + | + |but the ${"yield"} keyword is still required. + | + |For comprehensions that simply perform a side effect without yielding anything + |can also be written without parentheses but a ${"do"} keyword has to be included. + |For example, + | + |${"for (i <- 1 to 3) println(i)"} + | + | can be written as + | + |${"for i <- 1 to 3 do println(i) // notice the 'do' keyword"} + | + |""".stripMargin + } + } |