=== modified file 'shell.pl'
--- shell.pl	2012-05-19 09:32:20 +0000
+++ shell.pl	2012-05-17 22:58:49 +0000
@@ -1,9 +1,5 @@
 % vim: ft=prolog textwidth=80 tabstop=4 softtabstop=4 shiftwidth=4 expandtab
 
-%%%%%%%%%%%%%%%%%%%%%%%%%
-% Shell code generation %
-%%%%%%%%%%%%%%%%%%%%%%%%%
-
 :- module(shell, [
     op(600,xfy,($:-)),
 %   op(800,fx,(#)),
@@ -19,23 +15,14 @@
 :- use_module(generic).
 :- use_module(escape).
 
-% check for (incomplete) list containing character codes
-assert_string("").
-assert_string(Var) :- var(Var).
-assert_string([Code|Rest]) :-
-    integer(Code),
-    assert_string(Rest).
-
-assert_dcg_string(L1, L2) :-
-    assertion(assert_string(L1)),
-    assertion(assert_string(L2)).
+%%%%%%%%%%%%%%%%%%%%%%%%%
+% Shell code generation %
+%%%%%%%%%%%%%%%%%%%%%%%%%
 
 escape(In, Out) :- escape(sh, In, Out).
 
 escape_dcg(In) -->
-    assert_dcg_string,
     { escape(In, Out) },
-    assert_dcg_string,
     prepend(Out).
 
 escape_dcglist(List) -->
@@ -50,10 +37,8 @@
 runnable(chroot(_,_)).
 
 cmd_escape_runnable([Arg]) -->
-    assert_dcg_string,
     escape_dcg(Arg).
 cmd_escape_runnable([Arg1,Arg2|Rest]) -->
-    assert_dcg_string,
     escape_dcg(Arg1),
     prepend(" "),
     cmd_escape_runnable([Arg2|Rest]).
@@ -70,33 +55,28 @@
     cmd_escape_runnable(Runnable),
     prepend(" )").
 
-check_returncode --> assert_dcg_string, prepend(" || exit $?\n").
+check_returncode --> prepend(" || exit $?\n").
 
 cmd_tokens(verbatim(Verbatim)) -->
-    assert_dcg_string,
     str_dcg(Verbatim).
 
 cmd_tokens(Runnable) -->
-    assert_dcg_string,
     cmd_escape_runnable(Runnable),
     check_returncode.
 
 cmd_tokens(Runnable >> File) -->
-    assert_dcg_string,
     cmd_escape_runnable(Runnable),
     prepend(" >>"),
     escape_dcg(File),
     check_returncode.
 
 cmd_tokens(Runnable > File) -->
-    assert_dcg_string,
     cmd_escape_runnable(Runnable),
     prepend(" >"),
     escape_dcg(File),
     check_returncode.
 
 cmd_tokens(Variable = Value) -->
-    assert_dcg_string,
     str_dcg(Variable),
     prepend("="),
     (   { runnable(Value) }
@@ -121,7 +101,6 @@
     check_returncode.
 
 cmd_tokens(Variable = array(Runnable)) -->
-    assert_dcg_string,
     str_dcg(Variable),
     prepend("=( $("),
     cmd_escape_runnable(Runnable),
@@ -129,7 +108,6 @@
     check_returncode.
 
 cmd_tokens(comment(Text)) -->
-    assert_dcg_string,
     prepend("\n# "),
     { str(Text, String) },
     make_comment(String),