closure conversion first commit

closure_conversion.js

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+/* Takes an AST and converts all of the functions into closures.
+ * A closure is a pair of two things: an environment and a function
+ * The closure has the property that all of the free variables of the function
+ * are in the environment, or an exception is raised because the variable is not bound
+ * in the current environment.
+ * A free variable is simply those that are not in the list of formal parameters.
+ * We start with the global environment and traverse the AST. Every time a new function is entered
+ * the current environment gets extended with the formal parameters of the function.
+ * When a let is encountered the current environment also gets extended.
+ * The algorithm continues for any further function definitions in that branch
+ * otherwise it just stops for that particular branch and continues with the rest of the AST
+ *
+ * Therefore in order to call a closure one must first extract the actual function and then
+ * call the function with the environment associated with it.
+ * For the purposes of type checking it does not matter how the function gets called, the environment
+ * is only used for looking up the types of names. Formal parameters are given type variables.
+ */