Added closures support and related example

JAPL/interpreter.py

@@ -246,7 +246,7 @@ class Interpreter(object):
     def visit_function(self, statement):
         """Visits a function"""
 
-        function = JAPLFunction(statement)
+        function = JAPLFunction(statement, self.environment)
         self.environment.define(statement.name.lexeme, function)
 
     def exec(self, statement: Statement):

JAPL/types/native.py

@@ -37,14 +37,15 @@ class Type(Callable):
 class JAPLFunction(Callable):
     """A generic wrapper for user-defined functions"""
 
-    def __init__(self, declaration):
+    def __init__(self, declaration, closure):
        """Object constructor"""
 
        self.declaration = declaration
        self.arity = len(self.declaration.params)
+       self.closure = closure
 
     def call(self, interpreter, arguments):
-        scope = Environment(interpreter.globals)
+        scope = Environment(self.closure)
         for name, value in zip(self.declaration.params, arguments):
             scope.define(name.lexeme, value)
         interpreter.in_function = True

closure.jpl

@@ -0,0 +1,13 @@
+fun makeCounter() {
+  var i = 0;
+  fun count() {
+    i = i + 1;
+    print i;
+  }
+
+  return count;
+}
+
+var counter = makeCounter();
+counter(); // "1".
+counter(); // "2".

example.jpl

@@ -5,6 +5,8 @@
 2 + 2;
 -1 * 6;
 3 * (9 / 2);  // Parentheses for grouping
+8 % 2;  // Modulo division
+6 ** 9; // Exponentiation
 
 // Variable definition and assignment