Unify tuple types with tuples-of-types in the interpreter (#442)

executable_semantics/interpreter/value.h

@@ -6,6 +6,7 @@
 #define EXECUTABLE_SEMANTICS_INTERPRETER_VALUE_H_
 
 #include <list>
+#include <optional>
 #include <vector>
 
 #include "executable_semantics/ast/statement.h"
@@ -21,6 +22,11 @@ auto FindInVarValues(const std::string& field, VarValues* inits)
     -> const Value*;
 auto FieldsEqual(VarValues* ts1, VarValues* ts2) -> bool;
 
+// Finds the field in `*tuple` named `name`, and returns its address, or
+// nullopt if there is no such field. `*tuple` must be a tuple value.
+auto FindTupleField(const std::string& name, const Value* tuple)
+    -> std::optional<Address>;
+
 enum class ValKind {
   IntV,
   FunV,
@@ -36,7 +42,6 @@ enum class ValKind {
   FunctionTV,
   PointerTV,
   AutoTV,
-  TupleTV,
   StructTV,
   ChoiceTV,
   ContinuationTV,  // The type of a continuation.
@@ -102,11 +107,6 @@ struct Value {
       VarValues* methods;
     } struct_type;
 
-    struct {
-      std::string* name;
-      VarValues* fields;
-    } tuple_type;
-
     struct {
       std::string* name;
       VarValues* alternatives;
@@ -151,7 +151,6 @@ auto MakeFunTypeVal(const Value* param, const Value* ret) -> const Value*;
 auto MakePtrTypeVal(const Value* type) -> const Value*;
 auto MakeStructTypeVal(std::string name, VarValues* fields, VarValues* methods)
     -> const Value*;
-auto MakeTupleTypeVal(VarValues* fields) -> const Value*;
 auto MakeVoidTypeVal() -> const Value*;
 auto MakeChoiceTypeVal(std::string name, VarValues* alts) -> const Value*;