Start Evaluation

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

Sources/Parser/Expression.swift

@@ -0,0 +1,109 @@
+// 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/>.
+
+// expression: $ => choice($.identifier, $.integer, $.true, $.false, $.string_literal), // Very limited.
+
+import Common
+import SwiftTreeSitter
+import TreeSitterP4
+
+protocol ParseableEvaluatableExpression {
+  static func parse(node: Node, inTree tree: MutableTree) -> Result<EvaluatableExpression?>
+}
+
+extension Identifier: ParseableEvaluatableExpression {
+  static func parse(
+    node: SwiftTreeSitter.Node, inTree tree: SwiftTreeSitter.MutableTree
+  ) -> Result<EvaluatableExpression?> {
+
+    guard
+      let parser_statement_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (identifier) @identifier)"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let qr = parser_statement_query.execute(node: node, in: tree)
+
+    guard let result = qr.next() else {
+      return .Ok(.none)
+    }
+
+    return .Ok(Identifier(name: result.captures[0].node.text!))
+  }
+}
+
+extension P4BooleanValue: ParseableEvaluatableExpression {
+  static func parse(
+    node: SwiftTreeSitter.Node, inTree tree: SwiftTreeSitter.MutableTree
+  ) -> Result<EvaluatableExpression?> {
+
+    guard
+      let true_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (true))"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let true_qr = true_query.execute(node: node, in: tree)
+
+    if true_qr.next() != nil {
+      return .Ok(P4BooleanValue(withValue: true))
+    }
+
+    guard
+      let false_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (false))"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let false_qr = false_query.execute(node: node, in: tree)
+
+    if false_qr.next() != nil {
+      return .Ok(P4BooleanValue(withValue: false))
+    }
+    return .Ok(.none)
+  }
+}
+
+struct Expression {
+  public static func Parse(node: Node, inTree: MutableTree) -> Result<EvaluatableExpression> {
+    let localElementsParsers: [ParseableEvaluatableExpression.Type] = [
+      P4BooleanValue.self, Identifier.self,
+    ]
+
+    for le_parser in localElementsParsers {
+      if case Result.Ok(.some(let parsed)) = le_parser.parse(
+        node: node, inTree: inTree)
+      {
+        return .Ok(parsed)
+      }
+    }
+
+    return Result.Error(Error(withMessage: "Could not parse into expression."))
+  }
+}