Refactor Parsing/Runtime

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

Sources/P4Lang/Program.swift

@@ -0,0 +1,47 @@
+// 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 ExpressionStatement {
+  public init() {}
+}
+
+public struct Program {
+    public var types: [P4Type] = Array()
+
+    /// Find the program's main parser
+    /// 
+    /// Note: For now, the main parser is expected to be named main_parser.
+    public func starting_parser() -> Result<Parser> {
+        return self.find_parser(withName: Identifier(name: "main_parser"))
+    }
+
+    public func find_parser(withName name: Identifier) -> Result<Parser> {
+        for type in self.types {
+            guard let parser = type as? Parser else {
+                continue
+            }
+            if parser.name == name {
+                return .Ok(parser)
+            }
+        }
+        return .Error(Error(withMessage: "Could not find parser named \(name)"))
+    }
+
+    public init() {}
+}