compiler, runtime: Begin Runtime Refactor

Ultimately, the goal is to completely separate the compilation from
the runtime to make it possible to have the interpreter/evaluator
be "just another" entity that can perform meaningful work when
given a parsed GP4 program.

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

Sources/P4Runtime/Parser.swift

@@ -18,7 +18,11 @@
 import Common
 import P4Lang
 
-extension ParserAssignmentStatement: EvaluatableStatement {
+extension ParserAssignmentStatement: P4Statement {
+  public func effect(context: Common.CompilerContext) -> Common.CompilerContext {
+    return context
+  }
+
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
     let updated_execution = execution
     //let result = self.value.evaluate(execution: updated_execution)
@@ -192,3 +196,19 @@ extension ParserValue: LibraryCallable {
     }
   }
 }
+
+extension ParserState: P4Statement {
+  public func evaluate(
+    execution: Common.ProgramExecution
+  ) -> (Common.ControlFlow, Common.ProgramExecution) {
+    return (
+      ControlFlow.Error,
+      execution.setError(error: Error(withMessage: "Cannot evaluate unspecialized parser state"))
+    )
+  }
+
+  public func effect(context: Common.CompilerContext) -> Common.CompilerContext {
+    return context.update(
+      newTypes: context.types.declare(identifier: self.getName(), withValue: self))
+  }
+}