# HG changeset patch
# User Laman
# Date 2023-01-01 13:25:39
# Node ID c296b5584a9df3198a3b6f0e4026963027d941b1

basic variable declaration and arithmetic addition

diff --git a/src/jasinta.py b/src/jasinta.py
new file mode 100644
--- /dev/null
+++ b/src/jasinta.py
@@ -0,0 +1,123 @@
+from std import lib as stdlib
+
+
+class Undefined:
+	pass
+
+
+def evaluate(node, context):
+	if node is None:
+		return None
+
+	node_type = node["type"]
+	if node_type == "Identifier":
+		for ctx in reversed(context):
+			if node["name"] in ctx:
+				return ctx[node["name"]]
+		return Undefined
+
+	cls = node_index[node_type]
+	obj = cls(node)
+	return obj.eval(context)
+
+
+class Program:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		program_context = [*context, dict()]
+		for node in self.node["body"]:
+			evaluate(node, program_context)
+
+
+class ExpressionStatement:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		evaluate(self.node["expression"], context)
+
+
+class CallExpression:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		callee = evaluate(self.node["callee"], context)
+		arguments = [evaluate(arg, context) for arg in self.node["arguments"]]
+		return callee(*arguments)
+
+
+class MemberExpression:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		obj = evaluate(self.node["object"], context)
+		prop = evaluate(self.node["property"], [obj])
+		return prop
+
+
+class BinaryExpression:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		left = evaluate(self.node["left"], context)
+		right = evaluate(self.node["right"], context)
+
+		# in fact this doesn't follow JavaScript "+" semantics
+		if self.node["operator"] == "+":
+			return left+right
+		else:
+			raise NotImplementedError
+
+
+class EmptyStatement:
+	def __init__(self, node):
+		pass
+
+	def eval(self, context):
+		pass
+
+
+class VariableDeclaration:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		for node in self.node["declarations"]:
+			evaluate(node, context)
+
+
+class VariableDeclarator:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		value = evaluate(self.node["init"], context)
+
+		if self.node["id"]["type"] == "Identifier":
+			name = self.node["id"]["name"]
+			context[-1][name] = value
+		else:
+			raise NotImplementedError
+
+
+class Literal:
+	def __init__(self, node):
+		self.node = node
+
+	def eval(self, context):
+		return self.node["value"]
+
+
+node_index = {cls.__name__: cls for cls in [
+	Program, ExpressionStatement, CallExpression, MemberExpression, EmptyStatement, BinaryExpression,
+	VariableDeclaration, VariableDeclarator, Literal
+]}
+
+
+def interpret(parse_tree):
+	return evaluate(parse_tree, [stdlib])
diff --git a/src/std.py b/src/std.py
new file mode 100644
--- /dev/null
+++ b/src/std.py
@@ -0,0 +1,3 @@
+lib = {
+	"document": {"write": print}
+}