Support Setting Arrays/Fields

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

Sources/Common/Compiler.swift

@@ -0,0 +1,19 @@
+// 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/>.
+
+public typealias TypeScope = Scope<P4Type>
+public typealias TypeScopes = Scopes<P4Type>

Sources/Common/ProgramTypes.swift

@@ -117,6 +117,18 @@ public struct P4StructFields: Sequence, CustomStringConvertible, Equatable {
   public func count() -> Int {
     return self.fields.count
   }
+
+  public func describe_with_values(values: [P4Value?]) -> String {
+    assert(values.count == self.count())
+    return zip(self.fields, values).map() { (field, value) in 
+      let actual_value = if let v = value {
+        v.description
+      } else {
+        "Unset"
+      }
+      return String("\(field): \(actual_value)")
+    }.joined(separator: "; ")
+  }
 }
 
 /// The type for a P4 struct
@@ -159,7 +171,7 @@ public class P4StructValue: P4Value {
   }
 
   public var description: String {
-    return "Struct"
+    return "Struct: \(self.stype.fields.describe_with_values(values: self.values))"
   }
 
   public let stype: P4Struct
@@ -169,7 +181,7 @@ public class P4StructValue: P4Value {
     self.init(withType: type, andInitializers: [])
   }
 
-  public init(withType type: P4Struct, andInitializers initializers: [P4Value]) {
+  public init(withType type: P4Struct, andInitializers initializers: [P4Value?]) {
     var values: [P4Value?] = Array(repeating: .none, count: type.fields.count())
 
     for i in 0..<initializers.count {
@@ -188,6 +200,23 @@ public class P4StructValue: P4Value {
     }
     return .none
   }
+
+  public func set(field: P4StructFieldIdentifier, to: P4Value) -> Result<P4StructValue> {
+    var updated_values = self.values
+
+    for field_idx in 0..<stype.fields.count() {
+      if stype.fields.fields[field_idx] == field {
+        if !stype.fields.fields[field_idx].type.eq(rhs: to.type()) {
+          return .Error(Error(withMessage: "Cannot assign value with type \(to.type()) to field with type \(stype.fields.fields[field_idx].type))"))
+        }
+        updated_values[field_idx] = to
+        break
+      }
+    }
+
+    return .Ok(P4StructValue(withType: self.stype, andInitializers: updated_values))
+  }
+
 }
 
 /// A P4 boolean type
@@ -337,18 +366,25 @@ public class P4ArrayValue: P4Value {
     return P4Array(withValueType: self.vtype)
   }
 
-  let value: [EvaluatableExpression]
+  let value: [P4Value]
   let vtype: P4Type
 
-  public init(withType type: P4Type, withValue value: [EvaluatableExpression]) {
+  public init(withType type: P4Type, withValue value: [P4Value]) {
     self.vtype = type
     self.value = value
   }
 
-  public func access(_ index: Int) -> EvaluatableExpression {
+  public func access(_ index: Int) -> P4Value {
     return self.value[index]
   }
 
+  public func set(index: Int, to: P4Value) -> Result<P4ArrayValue> {
+    // TODO: Check for OOB
+    var updated_values = self.value
+    updated_values[index] = to
+    return Result.Ok(P4ArrayValue(withType: self.vtype, withValue: updated_values))
+  }
+
   public func eq(rhs: P4Value) -> Bool {
     guard rhs as? P4ArrayValue != nil else {
       return false

Sources/Common/Protocols.swift

@@ -40,3 +40,8 @@ public protocol P4Value: CustomStringConvertible {
   func type() -> any P4Type
   func eq(rhs: P4Value) -> Bool
 }
+
+public protocol EvaluatableLValueExpression: EvaluatableExpression {
+  func set(to: P4Value, inScopes scopes: ValueScopes, duringExecution execution: ProgramExecution) -> Result<(ValueScopes, P4Value)>
+  func check(to: EvaluatableExpression, inScopes scopes: TypeScopes) -> Result<()>
+}

Sources/P4Compiler/Expression.swift

@@ -27,6 +27,12 @@ protocol CompilableExpression {
   ) -> Result<EvaluatableExpression?>
 }
 
+protocol CompilableLValueExpression {
+  static func compile_as_lvalue(
+    node: Node, withContext context: CompilerContext
+  ) -> Result<EvaluatableLValueExpression?>
+}
+
 extension TypedIdentifier: CompilableExpression {
   static func compile(
     node: SwiftTreeSitter.Node, withContext context: CompilerContext
@@ -47,6 +53,26 @@ extension TypedIdentifier: CompilableExpression {
   }
 }
 
+extension TypedIdentifier: CompilableLValueExpression {
+  static func compile_as_lvalue(
+    node: SwiftTreeSitter.Node, withContext context: CompilerContext
+  ) -> Result<EvaluatableLValueExpression?> {
+
+    let expression = node.child(at: 0)!
+    #SkipUnlessNodeType<SwiftTreeSitter.Node, EvaluatableExpression?>(
+      node: expression, type: "identifier")
+
+    let maybe_parsed_expression =  TypedIdentifier.compile(node: node, withContext: context)
+    guard case .Ok(let maybe_typed_identifier)  = maybe_parsed_expression else {
+      return .Error(maybe_parsed_expression.error()!)
+    }
+
+    let typed_identifier_expression = maybe_typed_identifier as! TypedIdentifier
+
+    return Result.Ok(typed_identifier_expression)
+  }
+}
+
 extension P4BooleanValue: CompilableExpression {
   static func compile(
     node: SwiftTreeSitter.Node, withContext context: CompilerContext
@@ -130,13 +156,26 @@ struct Expression {
 struct LValue {
   public static func Compile(
     node: Node, withContext: CompilerContext
-  ) -> Result<Common.Identifier> {
-    return if let node_text_value = node.text {
-      .Ok(Common.Identifier(name: node_text_value))
-    } else {
-      .Error(Error(withMessage: "Could not parse an identifier for an LValue"))
+  ) -> Result<EvaluatableLValueExpression> {
+
+    // Try to compile all the expressions that are LValuable!
+
+    let lvalueParsers: [CompilableLValueExpression.Type] = [
+      TypedIdentifier.self, FieldAccessExpression.self, ArrayAccessExpression.self,
+    ]
+
+    for lvalue_parser in lvalueParsers {
+      switch lvalue_parser.compile_as_lvalue(
+        node: node, withContext: withContext)
+      {
+      case .Ok(.some(let parsed)): return .Ok(parsed)
+      case .Error(let e): return .Error(e)
+      default: continue
       }
     }
+
+    return Result.Error(Error(withMessage: "\(node.range): Could not parse into expression"))
+  }
 }
 
 struct Identifier {
@@ -477,3 +516,41 @@ extension FieldAccessExpression: CompilableExpression {
         withField: P4StructFieldIdentifier(id: field_name, withType: field_type)))
   }
 }
+
+extension FieldAccessExpression: CompilableLValueExpression {
+  static func compile_as_lvalue(
+    node: SwiftTreeSitter.Node, withContext context: CompilerContext
+  ) -> Result<EvaluatableLValueExpression?> {
+    let expression = node.child(at: 0)!
+    #SkipUnlessNodeType<Node, EvaluatableExpression?>(
+      node: expression, type: "fieldAccessExpression")
+
+    let maybe_parsed_expression =  FieldAccessExpression.compile(node: node, withContext: context)
+    guard case .Ok(let maybe_field_access_expression)  = maybe_parsed_expression else {
+      return .Error(maybe_parsed_expression.error()!)
+    }
+
+    let field_access_expression = maybe_field_access_expression as! FieldAccessExpression
+
+    return Result.Ok(field_access_expression)
+  }
+}
+
+extension ArrayAccessExpression: CompilableLValueExpression {
+  static func compile_as_lvalue(
+    node: SwiftTreeSitter.Node, withContext context: CompilerContext
+  ) -> Result<EvaluatableLValueExpression?> {
+    let expression = node.child(at: 0)!
+    #SkipUnlessNodeType<Node, EvaluatableExpression?>(
+      node: expression, type: "arrayAccessExpression")
+
+    let maybe_parsed_expression =  ArrayAccessExpression.compile(node: node, withContext: context)
+    guard case .Ok(let maybe_array_access_expression)  = maybe_parsed_expression else {
+      return .Error(maybe_parsed_expression.error()!)
+    }
+
+    let array_access_expression = maybe_array_access_expression as! ArrayAccessExpression
+
+    return Result.Ok(array_access_expression)
+  }
+}

Sources/P4Compiler/Parser.swift

@@ -22,65 +22,6 @@ import SwiftTreeSitter
 import TreeSitterExtensions
 import TreeSitterP4
 
-extension ParserAssignmentStatement: CompilableStatement {
-  public static func Compile(
-    node: Node, withContext context: CompilerContext
-  ) -> Result<(EvaluatableStatement, CompilerContext)> {
-
-    #RequireNodeType<Node, (EvaluatableStatement, CompilerContext)>(
-      node: node, type: "assignmentStatement", nice_type_name: "assignment statement")
-
-    guard let lvalue_node = node.child(at: 0),
-      lvalue_node.nodeType == "expression"
-    else {
-      return Result.Error(
-        ErrorOnNode(node: node, withError: "Missing lvalue in assignment statement"))
-    }
-
-    guard let rvalue_node = node.child(at: 2),
-      rvalue_node.nodeType == "expression"
-    else {
-      return Result.Error(
-        ErrorOnNode(node: node, withError: "Missing rvalue in assignment statement"))
-    }
-
-    let maybe_parsed_rvalue = Expression.Compile(
-      node: rvalue_node, withContext: context)
-    guard case Result.Ok(let rvalue) = maybe_parsed_rvalue else {
-      return Result.Error(maybe_parsed_rvalue.error()!)
-    }
-
-    let maybe_parsed_lvalue = LValue.Compile(node: lvalue_node, withContext: context)
-    guard case .Ok(let lvalue_identifier) = maybe_parsed_lvalue else {
-      return Result.Error(maybe_parsed_lvalue.error()!)
-    }
-    guard case Result.Ok(let lvalue_type) = context.names.lookup(identifier: lvalue_identifier)
-    else {
-      return Result.Error(
-        ErrorOnNode(
-          node: lvalue_node,
-          withError: "Cannot assign to variable \(lvalue_identifier) not in scope"))
-    }
-
-    if rvalue.type().eq(rhs: lvalue_type) {
-      return Result.Ok(
-        (
-          ParserAssignmentStatement(
-            withLValue: TypedIdentifier(name: lvalue_node.text!, withType: lvalue_type),
-            withValue: rvalue
-          ), context
-        ))
-
-    } else {
-      return Result.Error(
-        ErrorOnNode(
-          node: node,
-          withError:
-            "Cannot assign value of type \(rvalue.type()) to \(lvalue_identifier) (with type \(lvalue_type))"
-        ))
-    }
-  }
-}
 
 public struct Parser {
   public struct LocalElements {

Sources/P4Compiler/Statement.swift

@@ -246,3 +246,54 @@ extension ExpressionStatement: CompilableStatement {
     return Result.Ok((ExpressionStatement(), context))
   }
 }
+
+extension ParserAssignmentStatement: CompilableStatement {
+  public static func Compile(
+    node: Node, withContext context: CompilerContext
+  ) -> Result<(EvaluatableStatement, CompilerContext)> {
+
+    #RequireNodeType<Node, (EvaluatableStatement, CompilerContext)>(
+      node: node, type: "assignmentStatement", nice_type_name: "assignment statement")
+
+    guard let lvalue_node = node.child(at: 0),
+      lvalue_node.nodeType == "expression"
+    else {
+      return Result.Error(
+        ErrorOnNode(node: node, withError: "Missing lvalue in assignment statement"))
+    }
+
+    guard let rvalue_node = node.child(at: 2),
+      rvalue_node.nodeType == "expression"
+    else {
+      return Result.Error(
+        ErrorOnNode(node: node, withError: "Missing rvalue in assignment statement"))
+    }
+
+    let maybe_parsed_rvalue = Expression.Compile(
+      node: rvalue_node, withContext: context)
+    guard case Result.Ok(let rvalue) = maybe_parsed_rvalue else {
+      return Result.Error(maybe_parsed_rvalue.error()!)
+    }
+
+    let maybe_parsed_lvalue = LValue.Compile(node: lvalue_node, withContext: context)
+    guard case .Ok(let lvalue_identifier) = maybe_parsed_lvalue else {
+      return Result.Error(maybe_parsed_lvalue.error()!)
+    }
+
+    let check_result = lvalue_identifier.check(to: rvalue, inScopes: context.names)
+    guard case .Ok(_) = check_result else {
+      return Result.Error(
+        ErrorOnNode(
+          node: lvalue_node,
+          withError: "\(check_result.error()!)"))
+    }
+
+    return Result.Ok(
+      (
+        ParserAssignmentStatement(
+          withLValue: lvalue_identifier,
+          withValue: rvalue
+        ), context
+      ))
+  }
+}

Sources/P4Lang/Parser.swift

@@ -26,10 +26,10 @@ public struct LocalElement {
 }
 
 public struct ParserAssignmentStatement {
-  public let lvalue: TypedIdentifier
+  public let lvalue: EvaluatableLValueExpression
   public let value: EvaluatableExpression
 
-  public init(withLValue lvalue: TypedIdentifier, withValue value: EvaluatableExpression) {
+  public init(withLValue lvalue: EvaluatableLValueExpression, withValue value: EvaluatableExpression) {
     self.lvalue = lvalue
     self.value = value
   }

Sources/P4Runtime/Expressions.swift

@@ -93,6 +93,30 @@ extension TypedIdentifier: EvaluatableExpression {
   }
 }
 
+// Variables are evaluatable because they can be looked up by identifiers.
+extension TypedIdentifier: EvaluatableLValueExpression {
+  public func set(
+    to: any Common.P4Value, inScopes scopes: Common.ValueScopes, duringExecution execution: ProgramExecution
+  ) -> Common.Result<(Common.ValueScopes, P4Value)> {
+    if case .Error(let e) = scopes.lookup(identifier: self) {
+      return .Error(e)
+    }
+
+    return .Ok((scopes.set(identifier: self, withValue: to), to))
+  }
+
+  public func check(to: any Common.EvaluatableExpression, inScopes scopes: Common.TypeScopes) -> Result<()> {
+    guard case .Ok(let type) = scopes.lookup(identifier: self) else {
+      return .Error(Error(withMessage: "Cannot assign to identifier not in scope"))
+    }
+
+    if !type.eq(rhs: to.type()) {
+      return .Error(Error(withMessage: "Cannot assign value with type \(to.type()) to identifier \(self) with type \(type)"))
+    }
+    return .Ok(())
+  }
+}
+
 public func binary_equal_operator_evaluator(left: P4Value, right: P4Value) -> P4Value {
   if left.eq(rhs: right) {
     return P4BooleanValue(withValue: true)
@@ -141,7 +165,7 @@ extension ArrayAccessExpression: EvaluatableExpression {
     }
     let accessed = array.access(indexor_int.access())
 
-    return accessed.evaluate(execution: execution)
+    return .Ok(accessed)
   }
 
   public func type() -> any Common.P4Type {
@@ -149,6 +173,56 @@ extension ArrayAccessExpression: EvaluatableExpression {
   }
 }
 
+extension ArrayAccessExpression: EvaluatableLValueExpression {
+  public func set(
+    to: any Common.P4Value, inScopes scopes: Common.ValueScopes, duringExecution execution: ProgramExecution
+  ) -> Common.Result<(Common.ValueScopes, P4Value)> {
+    // For purposes of documentation, assume the field access expression we are evaluating is
+    // (strct_id)[indexor] = new_value
+    // where strct_id expands to
+    // (identifier.field_id1.field_id2...).field_id = new_field_value
+
+    // First, evaluate strct_id and make sure that it names a struct.
+    let maybe_value = self.name.evaluate(execution: execution)
+    guard case .Ok(let value) = maybe_value else {
+        return Result.Error(Error(withMessage: "\(self.name) cannot be evaluated: \(maybe_value.error()!)"))
+    }
+    guard let array_value = value as? P4ArrayValue else {
+        return Result.Error(Error(withMessage: "\(self.name) does not identify a struct"))
+    }
+
+    // Now, get the indexor!
+    let maybe_indexor_value = self.indexor.evaluate(execution: execution)
+    guard case .Ok(let indexor_value) = maybe_indexor_value else {
+        return Result.Error(Error(withMessage: "\(self.indexor) cannot be evaluated: \(maybe_indexor_value.error()!)"))
+    }
+    guard let indexor_int = indexor_value as? P4IntValue else {
+        return Result.Error(Error(withMessage: "\(self.indexor) cannot be used to index an array"))
+    }
+
+    // Now we have an array and an index!
+
+    // Update field_id of that structure and get the new structure value.
+    let set_result = array_value.set(index: indexor_int.access(), to: to)
+    guard case .Ok(let new_array_value) = set_result else {
+      return .Error(set_result.error()!)
+    }
+
+    let array_lvalue = self.name as! EvaluatableLValueExpression
+    return array_lvalue.set(to: new_array_value, inScopes: scopes, duringExecution: execution)
+  }
+
+  public func check(
+    to: any Common.EvaluatableExpression, inScopes scopes: Common.TypeScopes
+  ) -> Common.Result<()> {
+
+    if !self.type.value_type().eq(rhs: to.type()) {
+      return .Error(Error(withMessage: "Cannot assign value of type \(to.type()) to array with values of type \(self.name.type())"))
+    }
+    return .Ok(())
+  }
+}
+
 extension FieldAccessExpression: EvaluatableExpression {
   public func evaluate(execution: Common.ProgramExecution) -> Common.Result<any Common.P4Value> {
     let maybe_struct = self.strct.evaluate(execution: execution)
@@ -172,3 +246,48 @@ extension FieldAccessExpression: EvaluatableExpression {
     return self.field.type
   }
 }
+
+extension FieldAccessExpression: EvaluatableLValueExpression {
+  public func set(
+    to: any Common.P4Value, inScopes scopes: Common.ValueScopes, duringExecution execution: ProgramExecution
+  ) -> Common.Result<(Common.ValueScopes, P4Value)> {
+    // For purposes of documentation, assume the field access expression we are evaluating is
+    // (strct_id).field_id = new_field_value
+    // where strct_id expands to
+    // (identifier.field_id1.field_id2...).field_id = new_field_value
+
+    // First, evaluate strct_id and make sure that it names a struct.
+    let maybe_value = self.strct.evaluate(execution: execution)
+    guard case .Ok(let value) = maybe_value else {
+        return Result.Error(Error(withMessage: "\(self.strct) cannot be evaluated: \(maybe_value.error()!)"))
+    }
+
+    guard let struct_value = value as? P4StructValue else {
+        return Result.Error(Error(withMessage: "\(self.strct) does not identify a struct"))
+    }
+
+    // Now we know that struct_id identifies a structure value.
+
+    // Update field_id of that structure and get the new structure value.
+    let set_result = struct_value.set(field: self.field, to: to)
+    guard case .Ok(let new_struct_value) = set_result else {
+      return .Error(set_result.error()!)
+    }
+
+    // That new structure value should be assignable to the lvalue that is strct_id.
+    // We use recursion here -- ultimately finding our way to a TypedIdentifier that
+    // will update the scope. Pretty cool!
+    let struct_lvalue = self.strct as! EvaluatableLValueExpression
+    return struct_lvalue.set(to: new_struct_value, inScopes: scopes, duringExecution: execution)
+  }
+
+  public func check(
+    to: any Common.EvaluatableExpression, inScopes scopes: Common.TypeScopes
+  ) -> Common.Result<()> {
+
+    if !self.field.type.eq(rhs:to.type()) {
+      return .Error(Error(withMessage: "Cannot assign value of type \(to.type()) to field with type \(self.field.type)"))
+    }
+    return .Ok(())
+  }
+}

Sources/P4Runtime/Parser.swift

@@ -24,9 +24,13 @@ extension ParserAssignmentStatement: EvaluatableStatement {
     guard case Result.Ok(let value) = result else {
       return execution.setError(error: result.error()!)
     }
-    let updated_scopes = execution.scopes.set(identifier: self.lvalue, withValue: value)
 
-    execution.scopes = updated_scopes
+    let maybe_updated_scopes = self.lvalue.set(
+      to: value, inScopes: execution.scopes, duringExecution: execution)
+    guard case Result.Ok(let updated_scopes) = maybe_updated_scopes else {
+      return execution.setError(error: maybe_updated_scopes.error()!)
+    }
+    execution.scopes = updated_scopes.0
 
     return execution
   }