Refactor P4Compiler to P4Parser

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

Sources/P4Parser/Visitor.swift

@@ -0,0 +1,71 @@
+// p4rse, Copyright 2026, Will Hawkins
+//
+// This file is part of p4rse.
+//
+// This file is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+import Common
+
+public struct CSTVisitorDriver {
+  public init() {}
+
+  public func visit<T>(
+    expression: any CST.AnExpression, visitor: any CSTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch expression {
+    case let e as CST.BinaryOperatorExpression:
+      visitor.visit(node: e, driver: self, context: context)
+    case let e as CST.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 CST.AnState, visitor: any CSTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch state {
+    case let s as CST.ParserStateDirectTransition:
+      visitor.visit(node: s, driver: self, context: context)
+    case let s as CST.ParserStateNoTransition:
+      visitor.visit(node: s, driver: self, context: context)
+    case let s as CST.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 CST.Statement, visitor: any CSTVisitor<T>, context: T
+  ) -> Result<T> {
+    return switch statement {
+    case let s as CST.Parser: visitor.visit(node: s, driver: self, context: context)
+    default: .Error(Error(withMessage: "AST Statement Element Is Not Visitable"))
+    }
+  }
+
+  public func visit<T>(
+    program: CST.Program, visitor: any CSTVisitor<T>, context: T
+  ) -> Result<T> {
+
+    var context = context
+    for s in program.statements.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)
+  }
+}