Context aware clojures

Moved from dynamic scoping to static scoping.

examples/church.mq

@@ -0,0 +1,38 @@
+-- PAIR definition
+var pair = [x y | [z | z x y]];
+var car = [p | p [x y | x]];
+var cdr = [p | p [x y | y]];
+
+var x = pair 100 200;
+say (car x);
+say (cdr x);
+
+-- This two values should be builtin, but currently is not
+var true = (1 == 1);
+var false = (1 != 1);
+
+-- LIST definition
+var null = pair true true;
+var is_empty = car;
+var head = [list | car (cdr list)];
+var tail = [list | cdr (cdr list)];
+var cons = [head tail | pair false (pair head tail)];
+
+var for_each = [list iterator |
+	if (is_empty list) [| nil ] [|
+		iterator (head list);
+		for_each (tail list) iterator ]];
+
+var map = [list iterator |
+	if (is_empty list) [| null ] [|
+		cons (iterator (head list)) (map (tail list) iterator) ]];
+
+var foldr = [list init folder |
+	if (is_empty list)
+		[| init ]
+		[| foldr (tail list) (folder (head list) init) folder ]];
+
+var range = [start stop | if (start >= stop) [|cons start null] [|cons start (range (start+1) stop)]];
+
+var xs = range 1 5;
+say (foldr xs 1 [x y|x*y]);

src/interpreter.cc

@@ -151,6 +151,8 @@ Result<Value> Interpreter::eval(Ast &&ast)
 				assert(param.type == Ast::Type::Literal && param.token.type == Token::Type::Symbol, "Not a name in parameter section of Ast::lambda");
 				lambda.parameters.push_back(std::string(std::move(param).token.source));
 			}
+
+			lambda.context = env;
 			lambda.body = std::move(ast.arguments.back());
 			return Value::lambda(std::move(lambda));
 		}

src/musique.hh

@@ -427,8 +427,9 @@ struct Number
 
 std::ostream& operator<<(std::ostream& os, Number const& num);
 
-struct Value;
+struct Env;
 struct Interpreter;
+struct Value;
 
 using Function = std::function<Result<Value>(Interpreter &i, std::vector<Value>)>;
 
@@ -437,6 +438,7 @@ struct Lambda
 	Location location;
 	std::vector<std::string> parameters;
 	Ast body;
+	std::shared_ptr<Env> context;
 
 	Result<Value> operator()(Interpreter &i, std::vector<Value> params);
 };

src/value.cc

@@ -129,8 +129,9 @@ std::string_view type_name(Value::Type t)
 
 Result<Value> Lambda::operator()(Interpreter &i, std::vector<Value> arguments)
 {
-	// TODO Add some kind of scope guard
+	auto old_scope = std::exchange(i.env, context);
 	i.enter_scope();
+
 	assert(parameters.size() == arguments.size(), "wrong number of arguments");
 
 	for (usize j = 0; j < parameters.size(); ++j) {
@@ -140,6 +141,6 @@ Result<Value> Lambda::operator()(Interpreter &i, std::vector<Value> arguments)
 	Ast body_copy = body;
 	auto result = i.eval(std::move(body_copy));
 
-	i.leave_scope();
+	i.env = old_scope;
 	return result;
 }