diff --git a/c/env_unix.c b/c/env_unix.c
index 1e4ce31..24dd1ad 100644
--- a/c/env_unix.c
+++ b/c/env_unix.c
@@ -32,50 +32,40 @@ static const struct utsname *get_global_uname(void)
 
 const char *env_get_os_name(void) { return get_global_uname()->sysname; }
 
-static void push(value_t *tailp, value_t elt)
-{
-    value_t new_tail;
-
-    new_tail = cdr_(*tailp) = fl_cons(elt, FL_NIL);
-    *tailp = new_tail;
-}
-
-static void push_pair(value_t *tailp, const char *name, value_t value)
-{
-    push(tailp, fl_cons(symbol(name), value));
-}
-
 static value_t envst_language(void)
 {
-    value_t head, tail;
+    struct accum acc = ACCUM_EMPTY;
 
-    head = tail = fl_cons(symbol("language"), FL_NIL);
-    push_pair(&tail, "implementation-name", string_from_cstr("Up Scheme"));
-    push_pair(&tail, "implementation-version", string_from_cstr("0.1.0"));
-    return head;
+    accum_elt(&acc, symbol("language"));
+    accum_name_value(&acc, "implementation-name",
+                     string_from_cstr("Up Scheme"));
+    accum_name_value(&acc, "implementation-version",
+                     string_from_cstr("0.1.0"));
+    return acc.list;
 }
 
 static value_t envst_language_c(void)
 {
-    value_t head, tail;
+    struct accum acc = ACCUM_EMPTY;
 
-    head = tail = fl_cons(symbol("language"), FL_NIL);
-    push_pair(&tail, "implementation-name",
-              string_from_cstr(SCHEME_C_COMPILER_NAME));
-    push_pair(&tail, "implementation-version",
-              string_from_cstr(SCHEME_C_COMPILER_VERSION));
-    return head;
+    accum_elt(&acc, symbol("language"));
+    accum_name_value(&acc, "implementation-name",
+                     string_from_cstr(SCHEME_C_COMPILER_NAME));
+    accum_name_value(&acc, "implementation-version",
+                     string_from_cstr(SCHEME_C_COMPILER_VERSION));
+    return acc.list;
 }
+
 static value_t envst_os(void)
 {
-    value_t head, tail;
+    struct accum acc = ACCUM_EMPTY;
 
-    head = tail = fl_cons(symbol("os"), FL_NIL);
-    push_pair(&tail, "implementation-name",
-              string_from_cstr(get_global_uname()->sysname));
-    push_pair(&tail, "implementation-version",
-              string_from_cstr(get_global_uname()->release));
-    return head;
+    accum_elt(&acc, symbol("os"));
+    accum_name_value(&acc, "implementation-name",
+                     string_from_cstr(get_global_uname()->sysname));
+    accum_name_value(&acc, "implementation-version",
+                     string_from_cstr(get_global_uname()->release));
+    return acc.list;
 }
 
 static const char endianness[] =
@@ -89,25 +79,25 @@ static const char endianness[] =
 
 static value_t envst_computer(void)
 {
-    value_t head, tail;
+    struct accum acc = ACCUM_EMPTY;
 
-    head = tail = fl_cons(symbol("computer"), FL_NIL);
-    push_pair(&tail, "architecture",
-              string_from_cstr(get_global_uname()->machine));
-    push_pair(&tail, "cpu-bits", fixnum(sizeof(uintptr_t) * CHAR_BIT));
-    push_pair(&tail, "byte-order", symbol(endianness));
-    return head;
+    accum_elt(&acc, symbol("computer"));
+    accum_name_value(&acc, "architecture",
+                     string_from_cstr(get_global_uname()->machine));
+    accum_name_value(&acc, "cpu-bits", fixnum(sizeof(uintptr_t) * CHAR_BIT));
+    accum_name_value(&acc, "byte-order", symbol(endianness));
+    return acc.list;
 }
 
 value_t builtin_environment_stack(value_t *args, uint32_t nargs)
 {
-    value_t head, tail;
+    struct accum acc = ACCUM_EMPTY;
 
     (void)args;
     argcount("environment-stack", nargs, 0);
-    head = tail = fl_cons(envst_language(), FL_NIL);
-    push(&tail, envst_language_c());
-    push(&tail, envst_os());
-    push(&tail, envst_computer());
-    return head;
+    accum_elt(&acc, envst_language());
+    accum_elt(&acc, envst_language_c());
+    accum_elt(&acc, envst_os());
+    accum_elt(&acc, envst_computer());
+    return acc.list;
 }
diff --git a/c/scheme.h b/c/scheme.h
index 3ffae13..3f40a38 100644
--- a/c/scheme.h
+++ b/c/scheme.h
@@ -1002,6 +1002,22 @@ value_t fl_stringp(value_t *args, uint32_t nargs);
 value_t fl_string_reverse(value_t *args, uint32_t nargs);
 value_t fl_string_sub(value_t *args, uint32_t nargs);
 
+// util.c
+
+struct accum {
+    value_t list;
+    value_t tail;
+};
+
+#define ACCUM_EMPTY                    \
+    {                                  \
+        .list = FL_NIL, .tail = FL_NIL \
+    }
+
+void accum_elt(struct accum *accum, value_t elt);
+void accum_pair(struct accum *accum, value_t a, value_t d);
+void accum_name_value(struct accum *accum, const char *name, value_t value);
+
 // boot_image.c
 
 extern char boot_image[];
diff --git a/scripts/build.sh b/scripts/build.sh
index 9dad9eb..2adf87e 100755
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -37,6 +37,7 @@ o_files="$o_files table.o"
 o_files="$o_files text_ini.o"
 o_files="$o_files time_unix.o"
 o_files="$o_files utf8.o"
+o_files="$o_files util.o"
 default_cflags="-Wall -O2 -D NDEBUG -D USE_COMPUTED_GOTO -Wextra -std=gnu99 -Wno-strict-aliasing"
 default_lflags="-lm"
 case "$os" in
@@ -120,6 +121,7 @@ $CC $CFLAGS -c ../c/table.c
 $CC $CFLAGS -c ../c/text_ini.c
 $CC $CFLAGS -c ../c/time_unix.c
 $CC $CFLAGS -c ../c/utf8.c
+$CC $CFLAGS -c ../c/util.c
 
 $CC $CFLAGS -c ../c/boot_image.c
 $CC -o upscheme $o_files $LFLAGS