LambdaFree is an analysis pass for the SXML IntermediateLanguage, invoked from ClosureConvert.

## Description

This pass descends the entire SXML program and attaches a property to each Lambda PrimExp.t in the program. Then, you can use lambdaFree and lambdaRec to get free variables of that Lambda.

## Implementation

## Details and Notes

For Lambda-s bound in a Fun dec, lambdaFree gives the union of the frees of the entire group of mutually recursive functions. Hence, lambdaFree for every Lambda in a single Fun dec is the same. Furthermore, for a Lambda bound in a Fun dec, lambdaRec gives the list of other functions bound in the same dec defining that Lambda.

For example:

val rec f = fn x => ... y ... g ... f ... and g = fn z => ... f ... w ...

lambdaFree(fn x =>) = [y, w] lambdaFree(fn z =>) = [y, w] lambdaRec(fn x =>) = [g, f] lambdaRec(fn z =>) = [f]