diff --git a/Mmakefile b/Mmakefile
index 1598e5bb3..d288f1600 100644
--- a/Mmakefile
+++ b/Mmakefile
@@ -174,7 +174,7 @@ tags_profiler:
 
 #-----------------------------------------------------------------------------#
 
-configure: configure.in
+configure: configure.in aclocal.m4
 	autoconf
 
 config.status: configure VERSION
diff --git a/aclocal.m4 b/aclocal.m4
new file mode 100644
index 000000000..1103943d5
--- /dev/null
+++ b/aclocal.m4
@@ -0,0 +1,63 @@
+#-----------------------------------------------------------------------------#
+# Copyright (C) 1999 The University of Melbourne.
+# This file may only be copied under the terms of the GNU General
+# Public Licence - see the file COPYING in the Mercury distribution.
+#-----------------------------------------------------------------------------#
+#
+# aclocal.m4
+#
+# This file contains Mercury-specific autoconf tests.
+#
+# We ought to move most of the code in configure.in and
+# bindist/bindist.configure.in into this file...
+#
+#-----------------------------------------------------------------------------#
+#
+# Check for readline and related header files and libraries
+#
+AC_DEFUN(MERCURY_CHECK_READLINE,
+[
+
+# check for the readline header files
+AC_CHECK_HEADER(readline/readline.h, HAVE_READLINE_READLINE_H=1)
+if test "$HAVE_READLINE_READLINE_H" = 1; then
+	AC_DEFINE(HAVE_READLINE_READLINE)
+fi
+AC_CHECK_HEADER(readline/history.h, HAVE_READLINE_HISTORY_H=1)
+if test "$HAVE_READLINE_HISTORY_H" = 1; then
+	AC_DEFINE(HAVE_READLINE_HISTORY)
+fi
+
+# check for the readline library
+AC_CHECK_LIB(readline, readline, mercury_cv_have_readline=yes,
+	mercury_cv_have_readline=no)
+
+# check for the libraries that readline depends on
+if test $mercury_cv_have_readline = yes; then
+	MERCURY_MSG('looking for termcap or curses (needed by readline)...')
+	AC_CHECK_LIB(termcap, tgetent, mercury_cv_termcap_lib=-ltermcap,
+	 [AC_CHECK_LIB(curses,  tgetent, mercury_cv_termcap_lib=-lcurses,
+	  [AC_CHECK_LIB(ncurses, tgetent, mercury_cv_termcap_lib=-lncurses,
+	   mercury_cv_termcap_lib=none)])])
+fi
+
+# Now figure out whether we can use readline, and define variables according.
+# Note that on most systems, we don't actually need the header files in
+# order to use readline. (Ain't C grand? ;-).
+
+if test $mercury_cv_have_readline = no ||
+	test $mercury_cv_termcap_lib = none
+then
+	TERMCAP_LIBRARY=""
+	READLINE_LIBRARIES=""
+	AC_DEFINE(MR_NO_USE_READLINE)
+else
+	TERMCAP_LIBRARY="$mercury_cv_termcap_lib"
+	READLINE_LIBRARIES="-lreadline $TERMCAP_LIBRARY"
+fi
+AC_SUBST(TERMCAP_LIBRARY)
+AC_SUBST(READLINE_LIBRARIES)
+
+])
+
+#-----------------------------------------------------------------------------#
diff --git a/configure.in b/configure.in
index 6ca63e87d..d54a701d5 100644
--- a/configure.in
+++ b/configure.in
@@ -245,7 +245,7 @@ AC_CHECK_HEADER(dlfcn.h, HAVE_DLFCN_H=1)
 if test "$HAVE_DLFCN_H" = 1; then
 	AC_DEFINE(HAVE_DLFCN_H)
 fi
-AC_CHECK_LIB(dl,dlopen,DL_LIBRARY="-ldl",DL_LIBRARY="")
+AC_CHECK_LIB(dl, dlopen, DL_LIBRARY="-ldl", DL_LIBRARY="")
 AC_SUBST(DL_LIBRARY)
 
 # temporarily add $DL_LIBRARY to LIBS while we check for dlopen etc.
@@ -1814,13 +1814,12 @@ AC_SUBST_FILE(INIT_GRADE_OPTIONS)
 AC_SUBST_FILE(PARSE_GRADE_OPTIONS)
 AC_SUBST_FILE(FINAL_GRADE_OPTIONS)
 
-
 #-----------------------------------------------------------------------------#
 
 #
 # check whether we need -lsocket
 #
-AC_CHECK_LIB(socket,socket,SOCKET_LIBRARY=-lsocket,SOCKET_LIBRARY="")
+AC_CHECK_LIB(socket, socket, SOCKET_LIBRARY=-lsocket, SOCKET_LIBRARY="")
 AC_SUBST(SOCKET_LIBRARY)
 
 #
@@ -2000,7 +1999,8 @@ fi
 # restore the previous value of LIBS
 #
 LIBS="$save_LIBS"
-
+#-----------------------------------------------------------------------------#
+MERCURY_CHECK_READLINE
 #-----------------------------------------------------------------------------#
 AC_OUTPUT(Mmake.common scripts/Mmake.vars scripts/mmc scripts/mprof
 scripts/mercury_update_interface scripts/mgnuc scripts/ml
diff --git a/scripts/ml.in b/scripts/ml.in
index 27229d320..a86079c46 100644
--- a/scripts/ml.in
+++ b/scripts/ml.in
@@ -65,6 +65,8 @@ Debugging options:
 		then you don't need to explicitly specify \`--trace'.
 		Note that \`--trace' is incompatible with \`--static'
 		on some platforms (e.g. sparc-sun-solaris2.6).
+	-r-, --no-readline
+		Don't link in the GPL'd GNU Readline Library.
 	-g, --c-debug, --no-strip
 		Do not strip C debugging information.
 
@@ -111,6 +113,9 @@ SOCKET_LIBRARY="@SOCKET_LIBRARY@"
 # Likewise for -ldl (libdl.so), which is often needed for dlopen() etc.
 DL_LIBRARY="@DL_LIBRARY@"
 
+# Likewise for -lreadline -l{termcap,curses,ncurses}
+READLINE_LIBRARIES="@READLINE_LIBRARIES@"
+
 # If you change these, you will also need to change Mmake.common.in,
 # scripts/c2init.in, tools/bootcheck, tools/binary, tools/binary_step
 # and tools/linear.
@@ -121,6 +126,7 @@ BROWSER_LIB_NAME=mer_browser
 
 verbose=false
 trace=false
+readline=true
 case $FULLARCH in
 	*-win95|*-winnt|*-win32|*-cygwin32|*-cygwin)
 		# `gcc -s' is broken in gnu-win32
@@ -161,6 +167,12 @@ while : ; do
 	-t-|--no-trace)
 		trace=false
 		;;
+	-r|--readline)
+		readline=true
+		;;
+	-r-|--no-readline)
+		readline=false
+		;;
 	-g-|--no-c-debug|--strip)
 		strip=true
 		;;
@@ -365,13 +377,19 @@ case "$GRADE" in
 		;;
 esac
 
+case $readline in
+	true)	;;
+	false)	READLINE_LIBRARIES=
+		;;
+esac
+
 case $trace in
 	true)	TRACE_LIBS="-l$TRACE_LIB_NAME -l$BROWSER_LIB_NAME \
-			$SOCKET_LIBRARY $DL_LIBRARY"
+			$SOCKET_LIBRARY $DL_LIBRARY $READLINE_LIBRARIES"
 		TRACE_STATIC_LIBS="\
 			$LIBDIR/$GRADE/$FULLARCH/lib$TRACE_LIB_NAME.a \
 			$LIBDIR/$GRADE/$FULLARCH/lib$BROWSER_LIB_NAME.a \
-			$SOCKET_LIBRARY $DL_LIBRARY"
+			$SOCKET_LIBRARY $DL_LIBRARY $READLINE_LIBRARIES"
 		;;
 	false)	TRACE_LIBS=
 		TRACE_STATIC_LIBS=
diff --git a/trace/Mmakefile b/trace/Mmakefile
index 1eaa114ae..fa36e5eb2 100644
--- a/trace/Mmakefile
+++ b/trace/Mmakefile
@@ -16,13 +16,20 @@ include $(MERCURY_DIR)/Mmake.common
 
 CFLAGS		= -I$(MERCURY_DIR)/browser -I$(MERCURY_DIR)/library \
 		  -I$(MERCURY_DIR)/runtime -I$(MERCURY_DIR)/boehm_gc \
-		  -g $(DLL_CFLAGS) $(EXTRA_CFLAGS)
+		  -g $(DLL_CFLAGS)
 MGNUC		= MERCURY_C_INCL_DIR=. $(SCRIPTS_DIR)/mgnuc
-MGNUCFLAGS	= --no-ansi $(EXTRA_MGNUCFLAGS) $(CFLAGS)
+MGNUCFLAGS	= --no-ansi
 MOD2C		= $(SCRIPTS_DIR)/mod2c
 
 #-----------------------------------------------------------------------------#
 
+# mercury_readline.c #includes the GNU readline headers, which
+# lack prototypes and `const', so we need to disable warnings
+# when compiling that file.
+MGNUCFLAGS-mercury_trace_readline = --no-check
+
+#-----------------------------------------------------------------------------#
+
 # keep this list in alphabetical order, please
 HDRS		=	\
 			mercury_trace.h			\
@@ -32,6 +39,7 @@ HDRS		=	\
 			mercury_trace_external.h 	\
 			mercury_trace_help.h		\
 			mercury_trace_internal.h	\
+			mercury_trace_readline.h	\
 			mercury_trace_spy.h		\
 			mercury_trace_tables.h		\
 			mercury_trace_util.h
@@ -45,6 +53,7 @@ CFILES		= 	\
 			mercury_trace_external.c 	\
 			mercury_trace_help.c		\
 			mercury_trace_internal.c	\
+			mercury_trace_readline.c	\
 			mercury_trace_spy.c		\
 			mercury_trace_tables.c
 
diff --git a/trace/mercury_trace_internal.c b/trace/mercury_trace_internal.c
index 1a5c64896..c987dccdb 100644
--- a/trace/mercury_trace_internal.c
+++ b/trace/mercury_trace_internal.c
@@ -20,10 +20,13 @@
 #include "mercury_trace_spy.h"
 #include "mercury_trace_tables.h"
 #include "mercury_trace_util.h"
+#include "mercury_trace_readline.h"
 #include "mercury_layout_util.h"
 #include "mercury_array_macros.h"
 #include "mercury_getopt.h"
+
 #include "browse.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -36,9 +39,6 @@
 /* The initial size of arrays of words. */
 #define	MR_INIT_WORD_COUNT	20
 
-/* The initial size of arrays of characters. */
-#define	MR_INIT_BUF_LEN		80
-
 /* The initial number of lines in documentation entries. */
 #define	MR_INIT_DOC_CHARS	800
 
@@ -202,9 +202,8 @@ static	void	MR_trace_expand_aliases(char ***words,
 			int *word_max, int *word_count);
 static	bool	MR_trace_source(const char *filename);
 static	void	MR_trace_source_from_open_file(FILE *fp);
-static	char	*MR_trace_getline(const char *prompt, FILE *fp);
+static	char	*MR_trace_getline(const char *prompt);
 static	char	*MR_trace_getline_queue(void);
-static	char	*MR_trace_getline_raw(FILE *fp);
 static	void	MR_insert_line_at_head(const char *line);
 static	void	MR_insert_line_at_tail(const char *line);
 
@@ -262,7 +261,7 @@ MR_trace_event_internal(MR_Trace_Cmd_Info *cmd, bool interactive,
 	jumpaddr = NULL;
 
 	do {
-		line = MR_trace_getline("mdb> ", MR_mdb_in);
+		line = MR_trace_getline("mdb> ");
 		res = MR_trace_debug_cmd(line, cmd, event_info, &event_details,
 				&ancestor_level, &jumpaddr);
 	} while (res == KEEP_INTERACTING);
@@ -1303,9 +1302,8 @@ MR_trace_handle_cmd(char **words, int word_count, MR_Trace_Cmd_Info *cmd,
 			if (! confirmed) {
 				char	*line2;
 
-				line2 = MR_trace_getline(
-					"mdb: are you sure you want to quit? ",
-					MR_mdb_in);
+				line2 = MR_trace_getline("mdb: "
+					"are you sure you want to quit? ");
 				if (line2 == NULL) {
 					/* This means the user input EOF. */
 					confirmed = TRUE;
@@ -1930,7 +1928,7 @@ MR_trace_read_help_text(void)
 	int	i;
 
 	next_char_slot = 0;
-	while ((text = MR_trace_getline("cat> ", MR_mdb_in)) != NULL) {
+	while ((text = MR_trace_getline("cat> ")) != NULL) {
 		if (streq(text, "end")) {
 			free(text);
 			break;
@@ -2181,7 +2179,7 @@ MR_trace_source_from_open_file(FILE *fp)
 {
 	char	*line;
 
-	while ((line = MR_trace_getline_raw(fp)) != NULL) {
+	while ((line = MR_trace_readline_raw(fp)) != NULL) {
 		MR_insert_line_at_tail(line);
 	}
 
@@ -2190,14 +2188,15 @@ MR_trace_source_from_open_file(FILE *fp)
 
 /*
 ** If there any lines waiting in the queue, return the first of these.
-** If not, print the prompt, read a line from the given file, and return it
-** in a malloc'd buffer holding the line (without the final newline).
+** If not, print the prompt to MR_mdb_out, read a line from MR_mdb_in,
+** and return it in a malloc'd buffer holding the line (without the final
+** newline).
 ** If EOF occurs on a nonempty line, treat the EOF as a newline; if EOF
 ** occurs on an empty line, return NULL.
 */
 
 static char *
-MR_trace_getline(const char *prompt, FILE *fp)
+MR_trace_getline(const char *prompt)
 {
 	char	*line;
 
@@ -2207,10 +2206,8 @@ MR_trace_getline(const char *prompt, FILE *fp)
 	}
 
 	MR_trace_internal_interacting = TRUE;
-	fprintf(MR_mdb_out, "%s", prompt);
-	fflush(MR_mdb_out);
 
-	return MR_trace_getline_raw(fp);
+	return MR_trace_readline(prompt, MR_mdb_in, MR_mdb_out);
 }
 
 /*
@@ -2238,40 +2235,6 @@ MR_trace_getline_queue(void)
 	}
 }
 
-/*
-**	Read a line from a file, and return a pointer to a malloc'd buffer
-**	holding the line (without the final newline). If EOF occurs on a
-**	nonempty line, treat the EOF as a newline; if EOF occurs on an empty
-**	line, return NULL.
-*/
-
-static char *
-MR_trace_getline_raw(FILE *fp)
-{
-	char	*contents;
-	int	content_max;
-	int	c;
-	int	i;
-
-	contents = NULL;
-	content_max = 0;
-
-	i = 0;
-	while ((c = getc(fp)) != EOF && c != '\n') {
-		MR_ensure_big_enough(i, content, char, MR_INIT_BUF_LEN);
-		contents[i++] = c;
-	}
-
-	if (c == '\n' || i > 0) {
-		MR_ensure_big_enough(i, content, char, MR_INIT_BUF_LEN);
-		contents[i] = '\0';
-		return contents;
-	} else {
-		free(contents);
-		return NULL;
-	}
-}
-
 static void
 MR_insert_line_at_head(const char *contents)
 {
@@ -2321,7 +2284,7 @@ MR_trace_event_internal_report(MR_Trace_Cmd_Info *cmd,
 	/* We try to leave one line for the prompt itself. */
 	if (MR_scroll_control && MR_scroll_next >= MR_scroll_limit - 1) {
 	try_again:
-		buf = MR_trace_getline("--more-- ", MR_mdb_in);
+		buf = MR_trace_getline("--more-- ");
 		if (buf != NULL) {
 			for (i = 0; buf[i] != '\0' && MR_isspace(buf[i]); i++)
 				;
diff --git a/trace/mercury_trace_readline.c b/trace/mercury_trace_readline.c
new file mode 100644
index 000000000..898a9362a
--- /dev/null
+++ b/trace/mercury_trace_readline.c
@@ -0,0 +1,104 @@
+/*
+** Copyright (C) 1998-1999 The University of Melbourne.
+** This file may only be copied under the terms of the GNU Library General
+** Public License - see the file COPYING.LIB in the Mercury distribution.
+*/
+
+/*
+** A simple interface to read a line, normally done using GNU readline.
+**
+** This module is compiled with warnings disabled (mgnuc --no-check),
+** since the GNU readline headers don't use prototypes, const, etc.
+**
+** Main authors: fjh, zs.
+*/
+
+#include "mercury_imp.h"
+#include "mercury_trace_readline.h"
+#include "mercury_array_macros.h"
+#include "mercury_memory.h"
+#include "mercury_std.h"
+
+#ifndef MR_NO_USE_READLINE
+  #ifdef HAVE_READLINE_READLINE
+    #include "readline/readline.h"
+  #endif
+  #ifdef HAVE_READLINE_HISTORY
+    #include "readline/history.h"
+  #endif
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+
+/* The initial size of the array of characters used to hold the line. */
+#define	MR_INIT_BUF_LEN		80
+
+/*
+** Print the prompt to the `out' file, read a line from the `in' file,
+** and return it in a malloc'd buffer holding the line (without the final
+** newline).
+** If EOF occurs on a nonempty line, treat the EOF as a newline; if EOF
+** occurs on an empty line, return NULL.
+*/
+char *
+MR_trace_readline(const char *prompt, FILE *in, FILE *out)
+{
+	char	*line;
+
+#ifdef MR_NO_USE_READLINE
+
+	fprintf(out, "%s", prompt);
+	fflush(out);
+	line = MR_trace_readline_raw(in);
+
+#else /* use readline */
+
+	size_t	len;
+
+	rl_instream = in;
+	rl_outstream = out;
+
+	line = readline((char *) prompt);
+
+	if (line != NULL && line[0] != '\0') {
+		add_history(line);
+	}
+
+#endif
+
+	return line;
+}
+
+/*
+** Read a line from a file, and return a pointer to a malloc'd buffer
+** holding the line (without the final newline). If EOF occurs on a
+** nonempty line, treat the EOF as a newline; if EOF occurs on an empty
+** line, return NULL.
+*/
+char *
+MR_trace_readline_raw(FILE *fp)
+{
+	char	*contents;
+	int	content_max;
+	int	c;
+	int	i;
+
+	contents = NULL;
+	content_max = 0;
+
+	i = 0;
+	while ((c = getc(fp)) != EOF && c != '\n') {
+		MR_ensure_big_enough(i, content, char, MR_INIT_BUF_LEN);
+		contents[i++] = c;
+	}
+
+	if (c == '\n' || i > 0) {
+		MR_ensure_big_enough(i, content, char, MR_INIT_BUF_LEN);
+		contents[i] = '\0';
+		return contents;
+	} else {
+		free(contents);
+		return NULL;
+	}
+}