syntax.md: update syntax of for-expressions

Author: unkarjedy

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

@@ -2491,9 +2491,9 @@ object Parsers {
         GenFrom(pat, subExpr(), checkMode)
       }
 
-    /** ForExpr  ::= `for' (`(' Enumerators `)' | `{' Enumerators `}')
-     *                {nl} [`yield'] Expr
-     *            |  `for' Enumerators (`do' Expr | `yield' Expr)
+    /** ForExpr  ::=  ‘for’ ‘(’ Enumerators ‘)’ {nl} [‘do‘ | ‘yield’] Expr
+     *             |  ‘for’ ‘{’ Enumerators ‘}’ {nl} [‘do‘ | ‘yield’] Expr
+     *             |  ‘for’     Enumerators     {nl} (‘do‘ | ‘yield’) Expr
      */
     def forExpr(): Tree =
       atSpan(in.skipToken()) {

docs/docs/internals/syntax.md

@@ -263,9 +263,10 @@ BlockStat         ::=  Import
                     |  Expr1
                     |  EndMarker
 
-ForExpr           ::=  ‘for’ (‘(’ Enumerators ‘)’ | ‘{’ Enumerators ‘}’)        ForYield(enums, expr)
-                       {nl} [‘yield’] Expr
-                    |  ‘for’ Enumerators (‘do’ Expr | ‘yield’ Expr)             ForDo(enums, expr)
+ForExpr           ::=  ‘for’ ‘(’ Enumerators0 ‘)’ {nl} [‘do‘ | ‘yield’] Expr     ForYield(enums, expr) / ForDo(enums, expr)
+                    |  ‘for’ ‘{’ Enumerators0 ‘}’ {nl} [‘do‘ | ‘yield’] Expr
+                    |  ‘for’     Enumerators0     {nl} (‘do‘ | ‘yield’) Expr
+Enumerators0      ::=  {nl} Enumerators [semi]
 Enumerators       ::=  Generator {semi Enumerator | Guard}
 Enumerator        ::=  Generator
                     |  Guard

docs/docs/reference/syntax.md

@@ -259,8 +259,10 @@ BlockStat         ::=  Import
                     |  Expr1
                     |  EndMarker
 
-ForExpr           ::=  ‘for’ (‘(’ Enumerators ‘)’ | ‘{’ Enumerators ‘}’) {nl} [‘yield’] Expr
-                    |  ‘for’ Enumerators (‘do’ Expr | ‘yield’ Expr)
+ForExpr           ::=  ‘for’ ‘(’ Enumerators0 ‘)’ {nl} [‘do‘ | ‘yield’] Expr
+                    |  ‘for’ ‘{’ Enumerators0 ‘}’ {nl} [‘do‘ | ‘yield’] Expr
+                    |  ‘for’     Enumerators0     {nl} (‘do‘ | ‘yield’) Expr
+Enumerators0      ::=  {nl} Enumerators [semi]
 Enumerators       ::=  Generator {semi Enumerator | Guard}
 Enumerator        ::=  Generator
                     |  Guard