Start Rewrite

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

Sources/P4Compiler/Visitor.swift

@@ -0,0 +1,54 @@
+import Common
+
+public struct ASTVisitorDriver {
+  public init() {}
+
+  public func visit<T>(
+    expression: any AST.AnExpression, visitor: any ASTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch expression {
+    case let e as AST.BinaryOperatorExpression:
+      visitor.visit(node: e, driver: self, context: context)
+    case let e as AST.Literal: visitor.visit(node: e, driver: self, context: context)
+    default: .Error(Error(withMessage: "AST Expression Element Is Not Visitable"))
+    }
+  }
+
+  public func visit<T>(
+    state: any AST.AnState, visitor: any ASTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch state {
+    case let s as AST.ParserStateDirectTransition:
+      visitor.visit(node: s, driver: self, context: context)
+    case let s as AST.ParserStateNoTransition:
+      visitor.visit(node: s, driver: self, context: context)
+    case let s as AST.ParserStateSelectTransition:
+      visitor.visit(node: s, driver: self, context: context)
+    default: .Error(Error(withMessage: "AST State Element (\(state)) Is Not Visitable"))
+    }
+  }
+
+  public func visit<T>(
+    statement: any AST.AnStatement, visitor: any ASTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch statement {
+    case let s as AST.Parser: visitor.visit(node: s, driver: self, context: context)
+    default: .Error(Error(withMessage: "AST Statement Element Is Not Visitable"))
+    }
+  }
+
+  public func visit<T>(
+    program: AST.Program, visitor: any ASTVisitor<T>, context: T
+  ) -> Result<T> {
+
+    var context = context
+    for s in program.statements {
+      switch visit(statement: s, visitor: visitor, context: context) {
+      case .Ok(let c): context = c
+      case .Error(let e): return .Error(e)
+      }
+    }
+
+    return .Ok(context)
+  }
+}