Handle undefined value in type system.

New type code U indicates boxed undefined value.

1 files changed, 21 insertions, 1 deletions

diff --git a/cppawk-include/cons-priv.h b/cppawk-include/cons-priv.h
index 95c8cee..1e32624 100644
--- a/cppawk-include/cons-priv.h
+++ b/cppawk-include/cons-priv.h
@@ -172,8 +172,15 @@ function __symbolp(__obj)
 #define __symbolp(obj) (substr(obj, 1, 1) ~ /^S?$/)
 
 function __box(__raw,
+               __check,
                __case_temps)
 {
+  if (!__present(__raw))
+    return "U";
+
+  if (__present(__check))
+    __error("box; excess argument %s", __check)
+
   __case (__typecode(__raw)) {
     __of ("T", "S", "C")
       __cret ("T" __raw) // represent as unescaped string
@@ -183,17 +190,25 @@ function __box(__raw,
 }
 
 function __unbox(__obj,
+                 __check,
                  __case_temps)
 {
+  if (__present(__check))
+    __error("unbox; excess argument %s", __check)
+
   __case (__typecode(__obj)) {
     __of ("T", "S")
      __cret (substr(__obj, 2))
     __of ("C")
-      __error("unbox: %s looks like a cons", __obj, i)
+      __error("unbox: %s looks like a cons", __obj)
       __cbreak
+    __of ("U")
+      __cret(__check)
     __of ("")
       __cret("nil")
     __otherwise
+      if (!__numberp(__obj))
+        __error("unbox: %s isn't symbol, number or boxed string", __obj)
       __cret (__obj)
   }
 }
@@ -246,6 +261,9 @@ function __cdr(__cell,
 function __sexp(__obj,
                 __d, __x, __y, __case_temps)
 {
+  if (!__present(__obj))
+    __error("sexp: missing or undefined argument")
+
   __case (__typecode(__obj)) {
     __of ("C")
       __d = __cdr(__obj)
@@ -264,6 +282,8 @@ function __sexp(__obj,
       __cret ("\"" __bs_esc(substr(__obj, 2)) "\"")
     __of ("S")
       __cret (__bs_esc(substr(__obj, 2)))
+    __of ("U")
+      __cret ("#U")
   }
 
   if (__numberp(__obj)) {