public static MonkeyEnvironment NewEnclosedEnvironment(MonkeyEnvironment outer)
{
var env = NewEnvironment();
env.Outer = outer;
return(env);
}
private static MonkeyEnvironment ExtendFunctionEnv(MonkeyFunction fn, List <IMonkeyObject> args)
{
var env = MonkeyEnvironment.NewEnclosedEnvironment(fn.Env);
for (var i = 0; i < fn.Parameters.Count; i++)
{
env.Set(fn.Parameters[i].Value, args[i]);
}
return(env);
}
private static IMonkeyObject EvalIdentifier(Identifier node, MonkeyEnvironment env)
{
var(val, inCurrentEnvironment) = env.Get(node.Value);
if (inCurrentEnvironment)
{
return(val);
}
MonkeyBuiltin fn;
var inBuiltinEnvironment = MonkeyBuiltins.Builtins.TryGetValue(node.Value, out fn);
if (inBuiltinEnvironment)
{
return(fn);
}
return(NewError($"Identifier not found: {node.Value}"));
}
private static IMonkeyObject EvalBlockStatement(List <Statement> statements, MonkeyEnvironment env)
{
IMonkeyObject result = Evaluator.Null;
foreach (var stmt in statements)
{
result = Eval(stmt, env);
var rt = result.Type;
if (rt == ObjectType.ReturnValue || rt == ObjectType.Error)
{
// Compared to EvalProgram(), we don't unwrap the return
// value. Instead when an ReturnValue is encountered as the
// result of evaluating a statement, we return it to
// EvalProgram() for unwrapping. This halts outer block
// evaluation and bubbles up the result.
return(result);
}
}
return(result);
}
private static IMonkeyObject EvalIfExpression(IfExpression ie, MonkeyEnvironment env)
{
var condition = Eval(ie.Condition, env);
if (IsError(condition))
{
return(condition);
}
if (IsTruthy(condition))
{
return(Eval(ie.Consequence, env));
}
else if (ie.Alternative != null)
{
return(Eval(ie.Alternative, env));
}
return(Null);
}
private static List <IMonkeyObject> EvalExpressions(List <IExpression> exps, MonkeyEnvironment env)
{
var result = new List <IMonkeyObject>();
// Observe how, by definition, the arguments are evaluated left to
// right. Since the side effect of evaluating one argument might be
// relied on during the evaluation of the next, defining an explicit
// evaluation order is important.
foreach (var e in exps)
{
var evaluated = Eval(e, env);
if (IsError(evaluated))
{
return(new List <IMonkeyObject> {
evaluated
});
}
result.Add(evaluated);
}
return(result);
}
private static IMonkeyObject EvalProgram(List <Statement> statements, MonkeyEnvironment env)
{
IMonkeyObject result = Evaluator.Null;
foreach (var stmt in statements)
{
result = Eval(stmt, env);
// Prevents further evaluation if the result of the evaluation
// is a return statement. Note how we don't return MReturnValue
// directly, but unwrap its value. MReturnValue is an internal
// detail to allow Eval() to signal to its caller that it
// encountered and evaluated a return statement.
if (result is MonkeyReturnValue rv)
{
return(rv.Value);
}
if (result is MonkeyError e)
{
return(e);
}
}
return(result);
}
private static IMonkeyObject EvalHashLiteral(HashLiteral node, MonkeyEnvironment env)
{
var pairs = new Dictionary <HashKey, HashPair>();
foreach (var kv in node.Pairs)
{
var key = Eval(kv.Key, env);
if (IsError(key))
{
return(key);
}
if (key is IHashable k)
{
var value = Eval(kv.Value, env);
if (IsError(value))
{
return(value);
}
var hashKey = k.HashKey();
var hashPair = new HashPair {
Key = key, Value = value
};
pairs.Add(hashKey, hashPair);
}
else
{
return(NewError($"Unusable as hash key: {key.GetType()}"));
}
}
return(new MonkeyHash {
Pairs = pairs
});
}
public static IMonkeyObject Eval(INode node, MonkeyEnvironment env)
{
switch (node)
{
// Statements
case Program p:
return(EvalProgram(p.Statements, env));
case ExpressionStatement es:
return(Eval(es.Expression, env));
case BlockStatement bs:
return(EvalBlockStatement(bs.Statements, env));
case ReturnStatement rs:
{
var val = Eval(rs.ReturnValue, env);
// Check for errors whenever Eval is called inside Eval in
// order to stop errors from being passed around and
// bubbling up far from their origin.
if (IsError(val))
{
return(val);
}
return(new MonkeyReturnValue(val));
}
case LetStatement ls:
{
var val = Eval(ls.Value, env);
if (IsError(val))
{
return(val);
}
return(env.Set(ls.Name.Value, val));
}
// Expressions
case IntegerLiteral il:
return(new MonkeyInteger(il.Value));
case Boolean_ b:
return(NativeBoolToBooleanObject(b.Value));
case PrefixExpression pe:
{
var right = Eval(pe.Right, env);
if (IsError(right))
{
return(right);
}
return(EvalPrefixExpression(pe.Operator, right));
}
case InfixExpression ie:
{
var left = Eval(ie.Left, env);
if (IsError(left))
{
return(left);
}
var right = Eval(ie.Right, env);
return(IsError(right) ? right : EvalInfixExpression(ie.Operator, left, right));
}
case IfExpression ife:
return(EvalIfExpression(ife, env));
case Identifier i:
return(EvalIdentifier(i, env));
case FunctionLiteral fl:
{
return(new MonkeyFunction(fl.Parameters, fl.Body, env));
}
case CallExpression ce:
{
var function = Eval(ce.Function, env);
if (IsError(function))
{
return(function);
}
var args = EvalExpressions(ce.Arguments, env);
if (args.Count == 1 && IsError(args[0]))
{
return(args[0]);
}
return(ApplyFunction(function, args));
}
case ArrayLiteral al:
{
var elements = EvalExpressions(al.Elements, env);
if (elements.Count == 1 && IsError(elements[0]))
{
return(elements[0]);
}
return(new MonkeyArray(elements));
}
case IndexExpression ide:
{
var left = Eval(ide.Left, env);
if (IsError(left))
{
return(left);
}
var index = Eval(ide.Index, env);
if (IsError(index))
{
return(index);
}
return(EvalIndexExpression(left, index));
}
case StringLiteral sl:
return(new MonkeyString(sl.Value));
case HashLiteral hl:
return(EvalHashLiteral(hl, env));
default:
throw new Exception($"Invalid node type: {node.GetType()}");
}
}
public MonkeyFunction(List <Identifier> parameters, BlockStatement body, MonkeyEnvironment env)
{
Parameters = parameters;
Body = body;
Env = env;
}