compiler, runtime: Begin Runtime Refactor

Ultimately, the goal is to completely separate the compilation from
the runtime to make it possible to have the interpreter/evaluator
be "just another" entity that can perform meaningful work when
given a parsed GP4 program.

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

Sources/Common/Compiler.swift

@@ -26,3 +26,124 @@ public typealias TypeTypeScope = Scope<P4Type>
 
 /// Scopes that resolve type identifiers to their types.
 public typealias TypeTypeScopes = Scopes<P4Type>
+
+/// Context for compilation
+///
+/// It contains (at least) three important pieces of information:
+/// 1. Instances: A ``VarTypeScopes`` that contains information about instantiated objects
+/// (and their types) in scope
+/// 1. Types: A ``TypeTypeScopes`` that contains information about declared types in scope.
+/// 1. Expected Type: In certain situations, to typecheck an element of a P4 program requires
+/// knowledge of an expected type. For instance, when compiling a return statement, the
+/// compiler must know the return type of the function to type check.
+public struct CompilerContext {
+  public let instances: StaticVarValueScopes
+  public let types: TypeTypeScopes
+  public let externs: TypeTypeScopes
+  public let ffis: [P4FFI]
+  public let expected_type: P4QualifiedType?
+  public let extern_context: Bool
+
+  public init() {
+    instances = StaticVarValueScopes().enter()
+    types = TypeTypeScopes().enter()
+    externs = TypeTypeScopes().enter()
+    expected_type = .none
+    extern_context = false
+    ffis = Array()
+  }
+
+  public init(withInstances _instances: StaticVarValueScopes, withTypes _types: TypeTypeScopes) {
+    instances = _instances
+    types = _types
+    externs = TypeTypeScopes().enter()
+    expected_type = .none
+    extern_context = false
+    ffis = Array()
+  }
+
+  public init(
+    withInstances _instances: StaticVarValueScopes, withTypes _types: TypeTypeScopes,
+    withExpectation expectation: P4QualifiedType?, withExtern extern: Bool,
+    withExterns externs: TypeTypeScopes, withFFIs foreigns: [P4FFI]
+  ) {
+    instances = _instances
+    types = _types
+    expected_type = expectation
+    extern_context = extern
+    self.externs = externs
+    ffis = foreigns
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new instances.
+  ///
+  /// - Parameter instances: a ``VarTypeScopes`` with the updated instances for the newly created compiler context.
+  /// - Returns: A new compiler context based on the current but new instances.
+  public func update(newInstances instances: StaticVarValueScopes) -> CompilerContext {
+    return CompilerContext(
+      withInstances: instances, withTypes: self.types, withExpectation: self.expected_type,
+      withExtern: self.extern_context, withExterns: self.externs, withFFIs: self.ffis)
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new types.
+  ///
+  /// - Parameter types: a ``TypeTypeScopes`` with the updated types for the newly created compiler context.
+  /// - Returns: A new compiler context based on the current but new types.
+  public func update(newTypes types: TypeTypeScopes) -> CompilerContext {
+    return CompilerContext(
+      withInstances: self.instances, withTypes: types, withExpectation: self.expected_type,
+      withExtern: self.extern_context, withExterns: self.externs, withFFIs: self.ffis)
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new expected type.
+  ///
+  /// - Parameter expectation: a ``P4Type?`` to (re)set the type the compiler is expecting.
+  /// - Returns: A new compiler context based on the current but new expected type.
+  public func update(newExpectation expectation: P4QualifiedType?) -> CompilerContext {
+    return CompilerContext(
+      withInstances: self.instances, withTypes: self.types, withExpectation: expectation,
+      withExtern: self.extern_context, withExterns: self.externs, withFFIs: self.ffis)
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new extern context value.
+  ///
+  /// - Parameter extern: a ``Bool`` to (re)set whether the compiler is compiling in an extern context.
+  /// - Returns: A new compiler context based on the current but new extern context value.
+  public func update(newExtern extern: Bool) -> CompilerContext {
+    return CompilerContext(
+      withInstances: self.instances, withTypes: self.types, withExpectation: self.expected_type,
+      withExtern: extern, withExterns: self.externs, withFFIs: self.ffis)
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new externs.
+  ///
+  /// - Parameter externs: a ``TypeTypeScopes`` to (re)set the list of extern-al declarations.
+  /// - Returns: A new compiler context based on the current but new list of external-al declarations.
+  public func update(newExterns externs: TypeTypeScopes) -> CompilerContext {
+    return CompilerContext(
+      withInstances: self.instances, withTypes: self.types, withExpectation: self.expected_type,
+      withExtern: self.extern_context, withExterns: externs, withFFIs: self.ffis)
+  }
+
+  /// Update a compiler context
+  ///
+  /// Create a new compiler context based on the current but new FFIs.
+  ///
+  /// - Parameter foreigns: an array of ``P4FFI`` to (re)set the list of foreign functions.
+  /// - Returns: A new compiler context based on the current but with a new list of foreign functions.
+  public func update(newFFIs foreigns: [P4FFI]) -> CompilerContext {
+    return CompilerContext(
+      withInstances: self.instances, withTypes: self.types, withExpectation: self.expected_type,
+      withExtern: self.extern_context, withExterns: externs, withFFIs: foreigns)
+  }
+}