Commit d94c344

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Allow single case clauses as expressions

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3 files changed

+34

-5

lines changed

compiler/src/dotty/tools/dotc/parsing
- Parsers.scala
docs/_docs/internals
- syntax.md
tests/run
- single-case-expr.scala

3 files changed

+34

-5

lines changed

`‎compiler/src/dotty/tools/dotc/parsing/Parsers.scala‎`

Lines changed: 10 additions & 5 deletions

Original file line number	Diff line number	Diff line change
`@@ -2378,6 +2378,7 @@ object Parsers {`
`2378`	`2378`
`2379`	`2379`	/** Expr ::= [`implicit'] FunParams (‘=>’ \| ‘?=>’) Expr
`2380`	`2380`	`* \| TypTypeParamClause ‘=>’ Expr`
	`2381`	`+ * \| ExprCaseClause`
`2381`	`2382`	`* \| Expr1`
`2382`	`2383`	`* FunParams ::= Bindings`
`2383`	`2384`	`* \| id`
`@@ -2429,6 +2430,8 @@ object Parsers {`
`2429`	`2430`	`val arrowOffset = accept(ARROW)`
`2430`	`2431`	`val body = expr(location)`
`2431`	`2432`	`makePolyFunction(tparams, body, "literal", errorTermTree(arrowOffset), start, arrowOffset)`
	`2433`	`+ case CASE =>`
	`2434`	`+ singleCaseMatch()`
`2432`	`2435`	`case _ =>`
`2433`	`2436`	`val saved = placeholderParams`
`2434`	`2437`	`placeholderParams = Nil`
`@@ -2492,9 +2495,8 @@ object Parsers {`
`2492`	`2495`	`if in.token == CATCH then`
`2493`	`2496`	`val span = in.offset`
`2494`	`2497`	`in.nextToken()`
`2495`		`- (if in.token == CASE then Match(EmptyTree, caseClause(exprOnly = true) :: Nil)`
`2496`		`- else subExpr(),`
`2497`		`- span)`
	`2498`	`+ (if in.token == CASE then singleCaseMatch() else subExpr(),`
	`2499`	`+ span)`
`2498`	`2500`	`else (EmptyTree, -1)`
`2499`	`2501`
`2500`	`2502`	`handler match {`
`@@ -3188,9 +3190,9 @@ object Parsers {`
`3188`	`3190`	`case ARROW => atSpan(in.skipToken()):`
`3189`	`3191`	`if exprOnly then`
`3190`	`3192`	`if in.indentSyntax && in.isAfterLineEnd && in.token != INDENT then`
`3191`		`- warning(em"""Misleading indentation: this expression forms part of the preceding catch case.`
	`3193`	`+ warning(em"""Misleading indentation: this expression forms part of the preceding case.`
`3192`	`3194`	`\|If this is intended, it should be indented for clarity.`
`3193`		`- \|Otherwise, if the handler is intended to be empty, use a multi-line catch with`
	`3195`	`+ \|Otherwise, if the handler is intended to be empty, use a multi-line match or catch with`
`3194`	`3196`	`\|an indented case.""")`
`3195`	`3197`	`expr()`
`3196`	`3198`	`else block()`
`@@ -3206,6 +3208,9 @@ object Parsers {`
`3206`	`3208`	`CaseDef(pat, grd1, body)`
`3207`	`3209`	`}`
`3208`	`3210`
	`3211`	`+ def singleCaseMatch() =`
	`3212`	`+ Match(EmptyTree, caseClause(exprOnly = true) :: Nil)`
	`3213`	`+`
`3209`	`3214`	`/** TypeCaseClause ::= ‘case’ (InfixType \| ‘_’) ‘=>’ Type [semi]`
`3210`	`3215`	`*/`
`3211`	`3216`	`def typeCaseClause(): CaseDef = atSpan(in.offset) {`

`‎docs/_docs/internals/syntax.md‎`

Lines changed: 3 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -243,6 +243,7 @@ CapFilter ::= ‘.’ ‘as’ ‘[’ QualId ’]’`
`243`	`243`	```ebnf
`244`	`244`	`Expr ::= FunParams (‘=>’ \| ‘?=>’) Expr Function(args, expr), Function(ValDef([implicit], id, TypeTree(), EmptyTree), expr)`
`245`	`245`	`\| TypTypeParamClause ‘=>’ Expr PolyFunction(ts, expr)`
	`246`	`+ \| ExprCaseClause`
`246`	`247`	`\| Expr1`
`247`	`248`	`BlockResult ::= FunParams (‘=>’ \| ‘?=>’) Block`
`248`	`249`	`\| TypTypeParamClause ‘=>’ Block`
`@@ -295,6 +296,8 @@ SimpleExpr ::= SimpleRef`
`295`	`296`	`\| XmlExpr -- to be dropped`
`296`	`297`	`ColonArgument ::= colon [LambdaStart]`
`297`	`298`	`indent (CaseClauses \| Block) outdent`
	`299`	`+ \| colon LambdaStart expr ENDlambda -- ENDlambda is inserted for each production at next EOL`
	`300`	`+ -- does not apply if enclosed in parens`
`298`	`301`	`LambdaStart ::= FunParams (‘=>’ \| ‘?=>’)`
`299`	`302`	`\| TypTypeParamClause ‘=>’`
`300`	`303`	`Quoted ::= ‘'’ ‘{’ Block ‘}’`

`‎tests/run/single-case-expr.scala‎`

Lines changed: 21 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,21 @@`
	`1`	`+case class Foo(x: Int, y: Int)`
	`2`	`+@main def Test =`
	`3`	`+ val f: List[Int] => Int = case y :: ys => y`
	`4`	`+ val xs = List(1, 2, 3)`
	`5`	`+ assert(f(xs) == 1)`
	`6`	`+`
	`7`	`+ val g: Foo => Int = identity(case Foo(a, b) => a)`
	`8`	`+ val foo = Foo(1, 2)`
	`9`	`+ assert(g(foo) == 1)`
	`10`	`+`
	`11`	`+ val a1 = Seq((1, 2), (3, 4)).collect(case (a, b) if b > 2 => a)`
	`12`	`+ assert(a1 == Seq(3))`
	`13`	`+`
	`14`	`+ var a2 = Seq((1, 2), (3, 4)).collect(`
	`15`	`+ case (a, b) =>`
	`16`	`+ println(b)`
	`17`	`+ a`
	`18`	`+ )`
	`19`	`+ assert(a2 == Seq(1, 3))`
	`20`	`+`
	`21`	`+ val partial: PartialFunction[(Int, Int), Int] = case (a, b) if b > 2 => a`

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Commit d94c344

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3 files changed

3 files changed

`‎compiler/src/dotty/tools/dotc/parsing/Parsers.scala‎`

`‎docs/_docs/internals/syntax.md‎`

`‎tests/run/single-case-expr.scala‎`

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