diff --git a/os/pl-error.c b/os/pl-error.c
index 4de1cb131..05452544d 100755
--- a/os/pl-error.c
+++ b/os/pl-error.c
@@ -207,7 +207,7 @@ PL_get_module_ex(term_t name, module_t *m)
 }
 
 int
-PL_unify_bool_ex(term_t t, bool val)
+PL_unify_bool_ex(term_t t, int val)
 { GET_LD
   bool v;
 
diff --git a/os/pl-file.c b/os/pl-file.c
index a0a4e0707..fa7a5c03f 100755
--- a/os/pl-file.c
+++ b/os/pl-file.c
@@ -347,8 +347,8 @@ initIO(void)
   streamContext = newHTable(16);
   PL_register_blob_type(&stream_blob);
 
-  if ( false(Sinput, SIO_ISATTY) ||
-       false(Soutput, SIO_ISATTY) )
+  if ( False(Sinput, SIO_ISATTY) ||
+       False(Soutput, SIO_ISATTY) )
   { /* clear PLFLAG_TTY_CONTROL */
     PL_set_prolog_flag("tty_control", PL_BOOL, FALSE);
   }
@@ -1548,7 +1548,7 @@ readLine() reads a line from the terminal.  It is used only by the tracer.
 #define DEL 127
 #endif
 
-int
+bool
 readLine(IOSTREAM *in, IOSTREAM *out, char *buffer)
 { GET_LD
   int c;
@@ -1776,12 +1776,12 @@ set_stream(IOSTREAM *s, term_t stream, atom_t aname, term_t a ARG_LD)
     if ( !PL_get_atom_ex(a, &type) )
       return FALSE;
     if ( type == ATOM_text )
-    { if ( false(s, SIO_TEXT) && Ssetenc(s, LD->encoding, NULL) != 0 )
+    { if ( False(s, SIO_TEXT) && Ssetenc(s, LD->encoding, NULL) != 0 )
 	return PL_error(NULL, 0, NULL, ERR_PERMISSION,
 			ATOM_encoding, ATOM_stream, stream);
       s->flags |= SIO_TEXT;
     } else if ( type == ATOM_binary )
-    { if ( true(s, SIO_TEXT) && Ssetenc(s, ENC_OCTET, NULL) != 0 )
+    { if ( True(s, SIO_TEXT) && Ssetenc(s, ENC_OCTET, NULL) != 0 )
 	return PL_error(NULL, 0, NULL, ERR_PERMISSION,
 			ATOM_encoding, ATOM_stream, stream);
 
@@ -1922,7 +1922,7 @@ set_stream(IOSTREAM *s, term_t stream, atom_t aname, term_t a ARG_LD)
     else if ( val == ATOM_dos )
       s->newline = SIO_NL_DOS;
     else if ( val == ATOM_detect )
-    { if ( false(s, SIO_INPUT) )
+    { if ( False(s, SIO_INPUT) )
 	return PL_error(NULL, 0, "detect only allowed for input streams",
 			ERR_DOMAIN, ATOM_newline, a);
       s->newline = SIO_NL_DETECT;
@@ -2081,7 +2081,7 @@ PRED_IMPL("set_end_of_stream", 1, set_end_of_stream, 0)
 
 extern IOFUNCTIONS Smemfunctions;
 
-int
+bool
 tellString(char **s, size_t *size, IOENC enc)
 { GET_LD
   IOSTREAM *stream;
@@ -2095,8 +2095,8 @@ tellString(char **s, size_t *size, IOENC enc)
 }
 
 
-int
-toldString()
+bool
+toldString(void)
 { GET_LD
   IOSTREAM *s = getStream(Scurout);
 
@@ -3384,7 +3384,7 @@ findStreamFromFile(atom_t name, unsigned int flags)
   { stream_context *ctx = symb->value;
 
     if ( ctx->filename == name &&
-	 true(ctx, flags) )
+	 True(ctx, flags) )
     { s = symb->name;
       break;
     }
@@ -4652,7 +4652,7 @@ peek(term_t stream, term_t chr, int how ARG_LD)
 
   if ( !getInputStream(stream, how == PL_BYTE ? S_BINARY : S_TEXT, &s) )
     return FALSE;
-  if ( true(s, SIO_NBUF) || (s->bufsize && s->bufsize < PL_MB_LEN_MAX) )
+  if ( True(s, SIO_NBUF) || (s->bufsize && s->bufsize < PL_MB_LEN_MAX) )
   { releaseStream(s);
     return PL_error(NULL, 0, "stream is unbuffered", ERR_PERMISSION,
 		    ATOM_peek, ATOM_stream, stream);
diff --git a/os/pl-file.h b/os/pl-file.h
index e8aa1d95a..b86f16c73 100644
--- a/os/pl-file.h
+++ b/os/pl-file.h
@@ -46,7 +46,7 @@ COMMON(int)		streamStatus(IOSTREAM *s);
 COMMON(int)		setFileNameStream(IOSTREAM *s, atom_t name);
 COMMON(atom_t)		fileNameStream(IOSTREAM *s);
 COMMON(int)		getSingleChar(IOSTREAM *s, int signals);
-COMMON(int)		readLine(IOSTREAM *in, IOSTREAM *out, char *buffer);
+COMMON(bool)		readLine(IOSTREAM *in, IOSTREAM *out, char *buffer);
 COMMON(int)		LockStream(void);
 COMMON(int)		UnlockStream(void);
 COMMON(IOSTREAM *)	PL_current_input(void);
@@ -56,8 +56,8 @@ COMMON(int)		pl_seen(void);
 COMMON(int)		seeString(const char *s);
 COMMON(int)		seeingString(void);
 COMMON(int)		seenString(void);
-COMMON(int)		tellString(char **s, size_t *size, IOENC enc);
-COMMON(int)		toldString(void);
+COMMON(bool)		tellString(char **s, size_t *size, IOENC enc);
+COMMON(bool)		toldString(void);
 COMMON(void)		prompt1(atom_t prompt);
 COMMON(atom_t)		PrologPrompt(void);
 COMMON(int)		streamNo(term_t spec, int mode);
diff --git a/os/pl-fmt.c b/os/pl-fmt.c
index 3a92c7b8b..db42c80ca 100644
--- a/os/pl-fmt.c
+++ b/os/pl-fmt.c
@@ -361,6 +361,8 @@ get_chr_from_text(const PL_chars_t *t, int index)
       return t->text.t[index]&0xff;
     case ENC_WCHAR:
       return t->text.w[index];
+    case ENC_UTF8:
+      return t->text.w[index];
     default:
       assert(0);
       return 0;				/* not reached */
diff --git a/os/pl-option.h b/os/pl-option.h
index 704e6edba..a9221424b 100644
--- a/os/pl-option.h
+++ b/os/pl-option.h
@@ -45,7 +45,7 @@ typedef struct
   int		type;			/* Type of option */
 } opt_spec, *OptSpec;
 
-COMMON(int)		scan_options(term_t list, int flags, atom_t name,
+COMMON(bool)		scan_options(term_t list, int flags, atom_t name,
 				     const opt_spec *specs, ...);
 
 #endif /*OPTION_H_INCLUDED*/
diff --git a/os/pl-os.c b/os/pl-os.c
index 6a096bda9..c98490c7b 100755
--- a/os/pl-os.c
+++ b/os/pl-os.c
@@ -1847,7 +1847,7 @@ Sread_terminal(void *handle, char *buf, size_t size)
   int fd = (int)h;
   source_location oldsrc = LD->read_source;
 
-  if ( Soutput && true(Soutput, SIO_ISATTY) )
+  if ( Soutput && True(Soutput, SIO_ISATTY) )
   { if ( LD->prompt.next && ttymode != TTY_RAW )
       PL_write_prompt(TRUE);
     else
diff --git a/os/pl-prologflag.c b/os/pl-prologflag.c
index 1b80854d3..7fc0483fa 100755
--- a/os/pl-prologflag.c
+++ b/os/pl-prologflag.c
@@ -799,17 +799,17 @@ unify_prolog_flag_value(Module m, atom_t key, prolog_flag *f, term_t val)
 { GET_LD
 
   if ( key == ATOM_character_escapes )
-  { atom_t v = (true(m, M_CHARESCAPE) ? ATOM_true : ATOM_false);
+  { atom_t v = (True(m, M_CHARESCAPE) ? ATOM_true : ATOM_false);
 
     return PL_unify_atom(val, v);
   } else if ( key == ATOM_double_quotes )
   { atom_t v;
 
-    if ( true(m, DBLQ_CHARS) )
+    if ( True(m, DBLQ_CHARS) )
       v = ATOM_chars;
-    else if ( true(m, DBLQ_ATOM) )
+    else if ( True(m, DBLQ_ATOM) )
       v = ATOM_atom;
-    else if ( true(m, DBLQ_STRING) )
+    else if ( True(m, DBLQ_STRING) )
       v = ATOM_string;
     else
       v = ATOM_codes;
diff --git a/os/pl-read.c b/os/pl-read.c
index e7948b7d4..278325418 100644
--- a/os/pl-read.c
+++ b/os/pl-read.c
@@ -1265,7 +1265,7 @@ int process_comment;
 int rval;
 atom_t w;
 read_data rd;
-bool charescapes = -1;
+int charescapes = -1;
 atom_t dq = NULL_ATOM;
 atom_t mname = NULL_ATOM;
 fid_t fid = PL_open_foreign_frame();
diff --git a/os/pl-write.c b/os/pl-write.c
index fe9c1b29a..cdf9b3726 100644
--- a/os/pl-write.c
+++ b/os/pl-write.c
@@ -400,11 +400,11 @@ pl_write_term3(term_t stream, term_t term, term_t opts)
 { GET_LD
   bool quoted     = FALSE;
   bool ignore_ops = FALSE;
-  bool numbervars = -1;			/* not set */
+  int numbervars = -1;			/* not set */
   bool portray    = FALSE;
   term_t gportray = 0;
   bool bqstring   = truePrologFlag(PLFLAG_BACKQUOTED_STRING);
-  bool charescape = -1;			/* not set */
+  int charescape = -1;			/* not set */
   atom_t mname    = ATOM_user;
   atom_t attr     = ATOM_nil;
   atom_t blobs    = ATOM_nil;
@@ -467,7 +467,7 @@ pl_write_term3(term_t stream, term_t term, term_t opts)
   if ( charescape == TRUE ||
        (charescape == -1 
 #ifndef __YAP_PROLOG__
-&& true(options.module, M_CHARESCAPE)
+&& True(options.module, M_CHARESCAPE)
 #endif
 	) )
     options.flags |= PL_WRT_CHARESCAPES;
@@ -488,7 +488,7 @@ pl_write_term3(term_t stream, term_t term, term_t opts)
   if ( bqstring )   options.flags |= PL_WRT_BACKQUOTED_STRING;
   if ( !cycles )    options.flags |= PL_WRT_NO_CYCLES;
 
-  local_varnames = (varnames && false(&options, PL_WRT_NUMBERVARS));
+  local_varnames = (varnames && False(&options, PL_WRT_NUMBERVARS));
 
   BEGIN_NUMBERVARS(local_varnames);
   if ( varnames )
@@ -553,7 +553,7 @@ do_write2(term_t stream, term_t term, int flags)
     options.module    = MODULE_user;
     if ( options.module 
 #ifndef __YAP_PROLOG__
-	 && true(options.module, M_CHARESCAPE) 
+	 && True(options.module, M_CHARESCAPE) 
 #endif
 	 )
       options.flags |= PL_WRT_CHARESCAPES;