bugfix for predefined operations

src/compiler/GF/Compile/Compute/Concrete.hs

@@ -518,7 +518,8 @@ value2string =
       where
         all_capit = map toUpper
 --  value2string (b,f,ws) (VAlts vd vas) =
-    value2string st _     = st
+    value2string (Const _) _  = RunTime
+    value2string st        _  = st
 
 string2value s =
   case words s of

testsuite/compiler/compute/predef.gfs

@@ -1,6 +1,7 @@
 i -retain prelude/Predef.gfo
 cc length "abcd"
 cc length ("ab"++"cd")
+cc length nonExist
 cc <\x -> length x : Str -> Int>
 cc take 2 "abcd"
 cc drop 2 "abcd"

testsuite/compiler/compute/predef.gfs.gold

@@ -1,5 +1,6 @@
 4
 5
+Predef.length Predef.nonExist
 \v0 -> Predef.length v0
 "ab"
 "cd"