Issue #453 - Proper handing of EOF at the REPL

Finally handle EOF correctly and do not exit REPL if an expression evaluates to the EOF object. However, allow CTRL-d to exit the REPL.

CHANGELOG.md

@@ -22,6 +22,7 @@ Features
 Bug Fixes
 
 - Arthur Maciel replaced high resolution code in the runtime to use `clock_gettime` instead of `gettimeofday`.
+- Fixed the REPL to no longer automatically exit if an expression evaluates to EOF. However, the REPL will exit as a special case if the EOF character is entered directly, for example via CTRL-D on Linux. 
 
 ## 0.27 - March 5, 2021
 

scheme/repl.sld

@@ -47,11 +47,12 @@
           (newline)
           (repl))
         (display "cyclone> ")
-        (let ((c (eval (read))))
-          (cond
-            ((not (eof-object? c))
-             (write c)
+        (let ((obj (read)))
+          (if (eof-object? obj)
+              (newline) ;; Quick way to exit REPL
+              (let ((c (eval obj)))
+                (if (eof-object? c)
+                    (display "<EOF>")
+                    (write c))
                 (newline)
-             (repl))
-            (else 
-              (display "\n"))))))))
+                (repl))))))))