Fix multiple typeclass instance syntax

If an instance definition implements multiple traits, they are separated by commas.

Author: odersky

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

@@ -2555,7 +2555,7 @@ object Parsers {
       Template(constr, parents, Nil, EmptyValDef, Nil)
     }
 
-    /** InstanceDef    ::=  [id] InstanceParams [‘of’ ConstrApps] [TemplateBody]
+    /** InstanceDef    ::=  [id] InstanceParams [‘of’ ConstrApp {‘,’ ConstrApp}] [TemplateBody]
      *                   |  ‘val’ PatDef
      *                   |  ‘def’ MethodDef
      *  InstanceParams ::=  [DefTypeParamClause] {InstParamClause}
@@ -2577,7 +2577,7 @@ object Parsers {
         val parents =
           if (isIdent(nme.of)) {
             in.nextToken()
-            tokenSeparated(WITH, constrApp)
+            tokenSeparated(COMMA, constrApp)
           }
           else Nil
         newLineOptWhenFollowedBy(LBRACE)

docs/docs/internals/syntax.md

@@ -373,7 +373,8 @@ ClassConstr       ::=  [ClsTypeParamClause] [ConstrMods] ClsParamClauses
 ConstrMods        ::=  {Annotation} [AccessModifier]
 ObjectDef         ::=  id [Template]                                            ModuleDef(mods, name, template)  // no constructor
 EnumDef           ::=  id ClassConstr InheritClauses EnumBody                   EnumDef(mods, name, tparams, template)
-InstanceDef       ::=  [id] InstanceParams [‘of’ ConstrApps] [TemplateBody]
+InstanceDef       ::=  [id] InstanceParams [‘of’ ConstrApp {‘,’ ConstrApp}]
+                       [TemplateBody]
                     |  ‘val’ PatDef
                     |  ‘def’ MethodDef
 InstanceParams    ::=  [DefTypeParamClause] {InstParamClause}

docs/docs/reference/instances/instance-defs.md

@@ -168,7 +168,7 @@ Here is the new syntax of instance definitions, seen as a delta from the [standa
 ```
 TmplDef          ::=  ...
                   |  ‘instance’ InstanceDef
-InstanceDef      ::=  [id] InstanceParams [‘of’ ConstrApps] [TemplateBody]
+InstanceDef      ::=  [id] InstanceParams [‘of’ ConstrApp {‘,’ ConstrApp}] [TemplateBody]
 InstanceParams   ::=  [DefTypeParamClause] {InstParamClause}
 InstParamClause  ::=  ‘with’ (‘(’ [DefParams] ‘)’ | ContextTypes)
 ContextTypes     ::=  RefinedType {‘,’ RefinedType}

tests/run/tagless.scala

@@ -80,7 +80,7 @@ object Test extends App {
   }
   import Tree._
 
-  instance of Exp[Tree] with Mult[Tree] {
+  instance of Exp[Tree], Mult[Tree] {
     def lit(i: Int): Tree = Node("Lit", Leaf(i.toString))
     def neg(t: Tree): Tree = Node("Neg", t)
     def add(l: Tree, r: Tree): Tree = Node("Add", l , r)