Port ExitProc to Fusion.

runtime/src/main/fusion/modules/fusion/base.fusion

@@ -75,6 +75,9 @@ To use this dialect for your module, declare it as follows:
   (require "/fusion/private/control")
   (provide and or when unless cond)
 
+  (require "/fusion/private/raise")
+  (provide exit)
+
   (require "/fusion/equality")
   (provide = == === same ident)
 

runtime/src/main/fusion/modules/fusion/private/builtins.fusion

@@ -16,7 +16,6 @@
   (provide
     '#%top'
     apply
-    exit
     if
     is_blob
     is_bool

runtime/src/main/fusion/modules/fusion/private/kernel2.fusion

@@ -81,14 +81,6 @@ to the elements of `sequence`.  The `proc` is called in tail position.
     (java_new "dev.ionfusion.fusion.ApplyProc"))
 
 
-  (define_values (exit)
-    '''
-    (exit)
-Exits the running Fusion program.
-    '''
-    (java_new "dev.ionfusion.fusion.ExitProc"))
-
-
   (define_syntax if
     '''
     (if test then else)

runtime/src/main/fusion/modules/fusion/private/raise.fusion

@@ -7,6 +7,7 @@
 
   (provide
     assert
+    exit
     raise
     raise_argument_error
     raise_arity_error
@@ -88,4 +89,13 @@ Note that a `result_error` IS-A `contract_error`.
     '''
     (java_new "dev.ionfusion.fusion.RaiseResultErrorProc"))
 
+
+  (define_values (exit)
+    '''
+    (exit)
+
+Terminates the current Fusion thread.
+    '''
+    (lambda ()
+      (raise (java_new "dev.ionfusion.fusion.ExitException"))))
 )