src/HOL/Tools/Quickcheck/narrowing_generators.ML

           (unprefix "module Code where {" code)
         val _ = File.write code_file code'
         val _ = File.write narrowing_engine_file narrowing_engine
         val _ = File.write main_file main
         val executable = File.shell_path (Path.append in_path (Path.basic "isa_lsc"))
-        val cmd = "\"$ISABELLE_GHC\" -fglasgow-exts " ^
+        val cmd = "exec \"$ISABELLE_GHC\" -fglasgow-exts " ^
           (space_implode " " (map File.shell_path [code_file, narrowing_engine_file, main_file])) ^
           " -o " ^ executable ^ " && " ^ executable
       in
         bash_output cmd
       end