Merge pull request #6388 from dotty-staging/try-context-instance

Change syntax to instance-of-given.

Author: odersky

docs/docs/internals/syntax.md

@@ -385,6 +385,7 @@ InheritClauses    ::=  [‘extends’ ConstrApps] [‘derives’ QualId {‘,’
 ConstrApps        ::=  ConstrApp {‘with’ ConstrApp}
                     |  ConstrApp {‘,’ ConstrApp}
 ConstrApp         ::=  AnnotType {ArgumentExprs}                                Apply(tp, args)
+                    |  ‘(’ ConstrApp {‘given’ (InfixExpr | ParArgumentExprs)} ‘)’
 ConstrExpr        ::=  SelfInvocation
                     |  ConstrBlock
 SelfInvocation    ::=  ‘this’ ArgumentExprs {ArgumentExprs}

docs/docs/reference/contextual-instance/derivation.md

@@ -314,7 +314,7 @@ calling the `error` method defined in `scala.compiletime`.
 **Example:** Here is a slightly polished and compacted version of the code that's generated by inline expansion for the derived `Eql` instance of class `Tree`.
 
 ```scala
-instance [T] given (elemEq: Eql[T]) of Eql[Tree[T]] {
+instance [T] of Eql[Tree[T]] given (elemEq: Eql[T]) {
   def eql(x: Tree[T], y: Tree[T]): Boolean = {
     val ev = the[Generic[Tree[T]]]
     val mx = ev.reflect(x)

docs/docs/reference/contextual-instance/inferable-by-name-parameters.md

@@ -12,7 +12,7 @@ trait Codec[T] {
 
 instance intCodec of Codec[Int] = ???
 
-instance optionCodec[T] given (ev: => Codec[T]) of Codec[Option[T]] {
+instance optionCodec[T] of Codec[Option[T]] given (ev: => Codec[T]) {
   def write(xo: Option[T]) = xo match {
     case Some(x) => ev.write(x)
     case None =>

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

@@ -19,7 +19,7 @@ instance IntOrd of Ord[Int] {
     if (x < y) -1 else if (x > y) +1 else 0
 }
 
-instance ListOrd[T] given (ord: Ord[T]) of Ord[List[T]] {
+instance ListOrd[T] of Ord[List[T]] given (ord: Ord[T]) {
   def compare(xs: List[T], ys: List[T]): Int = (xs, ys) match {
     case (Nil, Nil) => 0
     case (Nil, _) => -1
@@ -42,9 +42,9 @@ The name of an implicit instance can be left out. So the instance definitions
 of the last section can also be expressed like this:
 ```scala
 instance of Ord[Int] { ... }
-instance [T] given (ord: Ord[T]) of Ord[List[T]] { ... }
+instance [T] of Ord[List[T]] given Ord[T] { ... }
 ```
-If a  name is not given, the compiler will synthesize one from the type(s) in the `for` clause.
+If a  name is not given, the compiler will synthesize one from the type(s) in the `of` clause.
 
 ## Alias Instances
 
@@ -67,12 +67,13 @@ Here is the new syntax of instance definitions, seen as a delta from the [standa
 ```
 TmplDef          ::=  ...
                   |  ‘instance’ InstanceDef
-InstanceDef      ::=  [id] InstanceParams InstanceBody
-InstanceParams   ::=  [DefTypeParamClause] {GivenParamClause}
+InstanceDef      ::=  [id] [DefTypeParamClause] InstanceBody
+InstanceBody     ::=  [‘of’ ConstrApp {‘,’ ConstrApp }] {GivenParamClause} [TemplateBody]
+                   |  ‘of’ Type {GivenParamClause} ‘=’ Expr
+ConstrApp        ::=  AnnotType {ArgumentExprs}
+                   |  ‘(’ ConstrApp {‘given’ (InfixExpr | ParArgumentExprs)} ‘)’
 GivenParamClause ::=  ‘given’ (‘(’ [DefParams] ‘)’ | GivenTypes)
-InstanceBody     ::=  [‘for’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
-                   |  ‘for’ Type ‘=’ Expr
 GivenTypes       ::=  AnnotType {‘,’ AnnotType}
 ```
-The identifier `id` can be omitted only if either the `for` part or the template body is present.
-If the `for` part is missing, the template body must define at least one extension method.
+The identifier `id` can be omitted only if either the `of` part or the template body is present.
+If the `of` part is missing, the template body must define at least one extension method.

docs/docs/reference/contextual-instance/multiversal-equality.md

@@ -98,7 +98,7 @@ class Box[T](x: T) derives Eql
 By the usual rules if [typeclass derivation](./derivation.html),
 this generates the following `Eql` instance in the companion object of `Box`:
 ```scala
-instance [T, U] given Eql[T, U] of Eql[Box[T], Box[U]] = Eql.derived
+instance [T, U] of Eql[Box[T], Box[U]] given Eql[T, U] = Eql.derived
 ```
 That is, two boxes are comparable with `==` or `!=` if their elements are. Examples:
 ```scala

docs/docs/reference/contextual-instance/relationship-implicits.md

@@ -21,7 +21,7 @@ Instance definitions can be mapped to combinations of implicit objects, classes
     ```
  2. Parameterized instance definitions are mapped to combinations of classes and implicit methods. E.g.,
     ```scala
-      instance ListOrd[T] given (ord: Ord[T]) of Ord[List[T]] { ... }
+      instance ListOrd[T] of Ord[List[T]] given (ord: Ord[T]) { ... }
     ```
     maps to
     ```scala