compiler, language, runtime: Separate Parser Type From Instances

In P4, parsers are considered types. Those parsers are instantiated.
The instantiated parsers are values. Previously, gp4 treated a parser
type and a parser value as identical. This PR makes that difference
clear _and_ sets the stage for the future.

TODO: Make the same distinction between control and action types and
values.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/P4Compiler/Declarations.swift

@@ -105,7 +105,7 @@ extension FunctionDeclaration: CompilableDeclaration {
       var function_scope = context.instances.enter()
       for parameter in function_parameters.parameters {
         function_scope = function_scope.declare(
-          identifier: parameter.name, withValue: parameter.type)
+          identifier: parameter.name, withValue: (parameter.type, .none))
       }
 
       let maybe_function_body = BlockStatement.Compile(
@@ -342,7 +342,7 @@ extension P4Lang.Parser: CompilableDeclaration {
     for parameter in parameter_list.parameters {
       current_context = current_context.update(
         newInstances: current_context.instances.declare(
-          identifier: parameter.name, withValue: parameter.type))
+          identifier: parameter.name, withValue: (parameter.type, .none)))
     }
 
     walker.next()
@@ -380,6 +380,7 @@ extension P4Lang.Parser: CompilableDeclaration {
       return .Error(Error(withMessage: "Missing parser states in parser declaration"))
     }
 
+    /// TODO: Handle extern parsers.
     switch Parser.Compile(
       withName: parser_name!, withParameters: parameter_list, node: current_node!,
       withContext: current_context)
@@ -392,10 +393,11 @@ extension P4Lang.Parser: CompilableDeclaration {
         (
           parser_declaration,
           context.extern_context
-            ? context
-            : context.update(
-              newInstances: updated_context.instances.declare(
-                identifier: parser.name, withValue: parser_declaration.identifier.type))
+            ? updated_context.update(
+              newExterns: updated_context.externs.declare(
+                identifier: parser.name, withValue: parser_declaration))
+            : updated_context.update(
+              newTypes: updated_context.types.declare(identifier: parser.name, withValue: parser))
         ))
     case Result.Error(let error): return .Error(error)
     }
@@ -450,7 +452,7 @@ extension Control: CompilableDeclaration {
     var control_scope = local_context.instances.enter()
     for parameter in control_parameters.parameters {
       control_scope = control_scope.declare(
-        identifier: parameter.name, withValue: parameter.type)
+        identifier: parameter.name, withValue: (parameter.type, .none))
     }
     local_context = local_context.update(newInstances: control_scope)
 
@@ -543,14 +545,15 @@ extension Control: CompilableDeclaration {
         ))
     }
 
+    let control = Control(
+      named: control_name, withParameters: control_parameters, withTable: tables[0],
+      withActions: Actions(withActions: actions), withApply: apply)
+
     let declared_control =
       Declaration(
         TypedIdentifier(
           id: control_name,
-          withType: P4QualifiedType(
-            Control(
-              named: control_name, withParameters: control_parameters, withTable: tables[0],
-              withActions: Actions(withActions: actions), withApply: apply))))
+          withType: P4QualifiedType(control)))
 
     // Don't forget to add the newly declared Control to the instance that we were given
     // (and not the one that we entered to do the parsing of this Control).
@@ -558,10 +561,12 @@ extension Control: CompilableDeclaration {
       (
         declared_control,
         context.extern_context
-          ? context
+          ? context.update(
+            newTypes: context.externs.declare(
+              identifier: control_name, withValue: declared_control))
           : context.update(
-            newInstances: context.instances.declare(
-              identifier: control_name, withValue: declared_control.identifier.type))
+            newTypes: context.types.declare(
+              identifier: control_name, withValue: control))
       ))
   }
 }
@@ -638,7 +643,7 @@ extension Action: Compilable {
     var function_scope = context.instances.enter()
     for parameter in action_parameters.parameters {
       function_scope = function_scope.declare(
-        identifier: parameter.name, withValue: parameter.type)
+        identifier: parameter.name, withValue: (parameter.type, .none))
     }
 
     let maybe_action_body = BlockStatement.Compile(