allow utilization of custom parser functions

src/main.js

@@ -11,12 +11,14 @@ export default function preprocess(opts) {
 				const state = {
 					failedIf: false
 				}
-				const parse = this.parse 
+				const parse = opts.parser ?? this.parse
+				const rollupThis = this
 
 				const comments = []
 				const ast = recast.parse(code, {
-					parser: this
+					parser: { parse }
 				})
+				
 				walk(ast, { //WALK CST FOR COMPTIME_VARS
 					enter(node, parent, prop, index) {
 						if (parent?.type === "MemberExpression" && parent?.property === node) {