diff --git a/GNUmakefile b/GNUmakefile
index f8aa33dc..5f23d70b 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -27,6 +27,7 @@ mes.o: mes.c mes.environment.h mes.environment.i mes.symbols.i
 mes.o: define.c define.environment.h define.environment.i
 mes.o: math.c math.environment.h math.environment.i
 mes.o: quasiquote.c quasiquote.environment.h quasiquote.environment.i
+mes.o: string.c string.environment.h string.environment.i
 mes.o: type.c type.environment.h type.environment.i
 
 clean:
diff --git a/mes.c b/mes.c
index cba0d05b..7c6d0ba9 100644
--- a/mes.c
+++ b/mes.c
@@ -66,6 +66,7 @@ scm temp_number = {NUMBER, .name="nul", .value=0};
 #include "define.environment.h"
 #include "quasiquote.environment.h"
 #include "math.environment.h"
+#include "string.environment.h"
 #include "mes.environment.h"
 
 scm *display_ (FILE* f, scm *x);
@@ -194,11 +195,6 @@ quasisyntax (scm *x)
   return cons (&symbol_quasisyntax, x);
 }
 
-#include "type.c"
-#include "define.c"
-#include "math.c"
-#include "quasiquote.c"
-
 //Library functions
 
 // Derived, non-primitives
@@ -598,87 +594,6 @@ make_vector (scm *n)
   return p;
 }
 
-scm *
-string (scm *x) ///((args . n))
-{
-  char buf[STRING_MAX] = "";
-  char *p = buf;
-  while (x != &scm_nil)
-    {
-      scm *s = car (x);
-      assert (s->type == CHAR);
-      *p++ = s->value;
-      x = cdr (x);
-    }
-  return make_string (buf);
-}
-
-scm *
-string_append (scm *x) ///((args . n))
-{
-  char buf[STRING_MAX] = "";
-
-  while (x != &scm_nil)
-    {
-      scm *s = car (x);
-      assert (s->type == STRING);
-      strcat (buf, s->name);
-      x = cdr (x);
-    }
-  return make_string (buf);
-}
-
-scm *
-list_to_string (scm *x)
-{
-  char buf[STRING_MAX] = "";
-  char *p = buf;
-  while (x != &scm_nil)
-    {
-      scm *s = car (x);
-      assert (s->type == CHAR);
-      *p++ = s->value;
-      x = cdr (x);
-    }
-  *p = 0;
-  return make_string (buf);
-}
-
-scm *
-string_length (scm *x)
-{
-  assert (x->type == STRING);
-  return make_number (strlen (x->name));
-}
-
-scm *
-string_ref (scm *x, scm *k)
-{
-  assert (x->type == STRING);
-  assert (k->type == NUMBER);
-  return make_char (x->name[k->value]);
-}
-
-scm *
-substring (scm *x) ///((args . n))
-{
-  assert (x->type == PAIR);
-  assert (x->car->type == STRING);
-  char const *s = x->car->name;
-  assert (x->cdr->car->type == NUMBER);
-  int start = x->cdr->car->value;
-  int end = strlen (s);
-  if (x->cdr->cdr->type == PAIR) {
-    assert (x->cdr->cdr->car->type == NUMBER);
-    assert (x->cdr->cdr->car->value <= end);
-    end = x->cdr->cdr->car->value;
-  }
-  char buf[STRING_MAX];
-  strncpy (buf, s+start, end - start);
-  buf[end-start] = 0;
-  return make_string (buf);
-}
-
 scm *
 length (scm *x)
 {
@@ -828,15 +743,6 @@ char_to_integer (scm *x)
   return make_number (x->value);
 }
 
-scm *
-number_to_string (scm *x)
-{
-  assert (x->type == NUMBER);
-  char buf[STRING_MAX];
-  sprintf (buf,"%d", x->value);
-  return make_string (buf);
-}
-
 scm *
 builtin_exit (scm *x)
 {
@@ -844,20 +750,6 @@ builtin_exit (scm *x)
   exit (x->value);
 }
 
-scm *
-string_to_symbol (scm *x)
-{
-  assert (x->type == STRING);
-  return make_symbol (x->name);
-}
-
-scm *
-symbol_to_string (scm *x)
-{
-  assert (x->type == SYMBOL);
-  return make_string (x->name);
-}
-
 scm *
 vector_to_list (scm *v)
 {
@@ -1184,6 +1076,7 @@ mes_environment () ///((internal))
   a = cons (cons (&symbol_quote, &scm_quote), a);
   a = cons (cons (&symbol_syntax, &scm_syntax), a);
 
+#include "string.environment.i"
 #include "math.environment.i"
 #include "mes.environment.i"
 #include "define.environment.i"
@@ -1226,6 +1119,12 @@ read_file (scm *e, scm *a)
 #endif
 }
 
+#include "type.c"
+#include "define.c"
+#include "math.c"
+#include "quasiquote.c"
+#include "string.c"
+
 int
 main (int argc, char *argv[])
 {
diff --git a/string.c b/string.c
new file mode 100644
index 00000000..d0f792a6
--- /dev/null
+++ b/string.c
@@ -0,0 +1,123 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * Mes --- Maxwell Equations of Software
+ * Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
+ *
+ * This file is part of Mes.
+ *
+ * Mes is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+scm *
+string (scm *x) ///((args . n))
+{
+  char buf[STRING_MAX] = "";
+  char *p = buf;
+  while (x != &scm_nil)
+    {
+      scm *s = car (x);
+      assert (s->type == CHAR);
+      *p++ = s->value;
+      x = cdr (x);
+    }
+  return make_string (buf);
+}
+
+scm *
+string_append (scm *x) ///((args . n))
+{
+  char buf[STRING_MAX] = "";
+
+  while (x != &scm_nil)
+    {
+      scm *s = car (x);
+      assert (s->type == STRING);
+      strcat (buf, s->name);
+      x = cdr (x);
+    }
+  return make_string (buf);
+}
+
+scm *
+list_to_string (scm *x)
+{
+  char buf[STRING_MAX] = "";
+  char *p = buf;
+  while (x != &scm_nil)
+    {
+      scm *s = car (x);
+      assert (s->type == CHAR);
+      *p++ = s->value;
+      x = cdr (x);
+    }
+  *p = 0;
+  return make_string (buf);
+}
+
+scm *
+string_length (scm *x)
+{
+  assert (x->type == STRING);
+  return make_number (strlen (x->name));
+}
+
+scm *
+string_ref (scm *x, scm *k)
+{
+  assert (x->type == STRING);
+  assert (k->type == NUMBER);
+  return make_char (x->name[k->value]);
+}
+
+scm *
+substring (scm *x) ///((args . n))
+{
+  assert (x->type == PAIR);
+  assert (x->car->type == STRING);
+  char const *s = x->car->name;
+  assert (x->cdr->car->type == NUMBER);
+  int start = x->cdr->car->value;
+  int end = strlen (s);
+  if (x->cdr->cdr->type == PAIR) {
+    assert (x->cdr->cdr->car->type == NUMBER);
+    assert (x->cdr->cdr->car->value <= end);
+    end = x->cdr->cdr->car->value;
+  }
+  char buf[STRING_MAX];
+  strncpy (buf, s+start, end - start);
+  buf[end-start] = 0;
+  return make_string (buf);
+}
+
+scm *
+number_to_string (scm *x)
+{
+  assert (x->type == NUMBER);
+  char buf[STRING_MAX];
+  sprintf (buf,"%d", x->value);
+  return make_string (buf);
+}
+
+scm *
+string_to_symbol (scm *x)
+{
+  assert (x->type == STRING);
+  return make_symbol (x->name);
+}
+
+scm *
+symbol_to_string (scm *x)
+{
+  assert (x->type == SYMBOL);
+  return make_string (x->name);
+}