Issue #257 - Prevent possible infinite loop

CHANGELOG.md

@@ -16,6 +16,7 @@ Bug Fixes
 - Fixed an off-by-one error in `read-line` where the function erroneously reported an extra character was read from `stdin`. Thanks to wasamasa for the bug report.
 - Fixed a CPS optimization issue where multiple copies of the same lambda are introduced during beta expansion, which causes the optimizer to potentially pick up the wrong value when optimizing-out function calls later on. Thanks to @Chant on Github for providing the report and a test program demonstrating the issue.
 - Updated the parser to recognize mnemonic escapes (EG: `\n`, `\a`, etc) and inline hex escapes as part of a symbol.
+- Prevent a possible infinite loop during beta expansion optimization.
 
 ## 0.7.2 - February 15, 2018
 

scheme/cyclone/cps-optimizations.sld

@@ -1377,7 +1377,8 @@
         (map cons (ast:lambda-args fnc) (cdr exp)))
       (define (replace ref renamed)
         (let ((r (assoc ref formals/actuals)))
-            (if r 
+            (if (and r 
+                     (not (eq? (car r) (cdr r)))) ;; Prevent an inf loop
                 (scan (cdr r) renamed) 
                 ;ref
                 (let ((rn (assoc ref renamed)))