diff --git a/examples/examples.mk b/examples/examples.mk
index 2cd6e636..e510698d 100644
--- a/examples/examples.mk
+++ b/examples/examples.mk
@@ -114,6 +114,18 @@ o/$(MODE)/examples/hellojs.com.dbg:			\
 		$(APE)
 	@$(APELINK)
 
+o/$(MODE)/examples/ispell.com.dbg:			\
+		$(EXAMPLES_DEPS)			\
+		o/$(MODE)/examples/ispell.o		\
+		o/$(MODE)/usr/share/dict/words.zip.o	\
+		o/$(MODE)/examples/examples.pkg		\
+		$(CRT)					\
+		$(APE)
+	@$(APELINK)
+
+o/$(MODE)/usr/share/dict/words: usr/share/dict/words.gz
+	$(GZ) $(ZFLAGS) <$< >$@
+
 .PHONY: o/$(MODE)/examples
 o/$(MODE)/examples:					\
 		o/$(MODE)/examples/package		\
diff --git a/examples/ispell.c b/examples/ispell.c
new file mode 100644
index 00000000..816b83cf
--- /dev/null
+++ b/examples/ispell.c
@@ -0,0 +1,157 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/alg/alg.h"
+#include "libc/alg/arraylist.h"
+#include "libc/bits/bits.h"
+#include "libc/calls/calls.h"
+#include "libc/conv/conv.h"
+#include "libc/log/check.h"
+#include "libc/log/log.h"
+#include "libc/macros.h"
+#include "libc/mem/mem.h"
+#include "libc/stdio/stdio.h"
+#include "libc/str/str.h"
+#include "libc/str/tpdecode.h"
+#include "libc/sysv/consts/fileno.h"
+#include "libc/x/x.h"
+
+/**
+ * @fileoverview Simple Interactive Spell Checker.
+ *
+ * This is an attempt to get spell checking to work in Emacs across
+ * platforms. While the computer science behind spell checking is very
+ * simple, unfortunately Emacs probes all these System Five spell progs
+ * similar to how websites have been known to probe User-Agent strings.
+ *
+ * Here's how we believe the repl works:
+ *
+ *     $ make -j8 o//examples/ispell.com
+ *     $ o//examples/ispell.com
+ *     @(#) Cosmopolitan Ispell Version 3.4.00 8 Feb 2015
+ *     word: hello
+ *     ok
+ *     word: héllo
+ *     how about: hills, hello, hilly, jello
+ *     word: lova
+ *     how about: diva, dona, dora, dove, elva, fora, hove, iota
+ *     word: hecruhecrue
+ *     not found
+ *
+ * The dictionary for this program is embedded as a text file within the
+ * zip structure of the binary. It can be edited after distribution.
+ *
+ * It's possible to go even fancier than what this code is doing, by
+ * using cmudict phonemes, bloom filters, unicode tables e.g. e vs. é,
+ * and even doing ML similar to Google's online spell checker.
+ *
+ * TODO: Figure out why Emacs rejects this interface.
+ */
+
+#define MISSING_LETTER_DISTANCE  5
+#define MAX_NEARBY_WORD_DISTANCE 6
+#define MAX_NEARBY_RESULTS       8
+
+FILE *f;
+char *line;
+size_t linesize;
+const char *query;
+struct critbit0 words; /* does O(log 𝑛) fast path lookup */
+
+struct NearbyWords {
+  size_t i, n;
+  struct WordMatch {
+    long dist;
+    char *word;
+  } * p;
+} nearby;
+
+long WordDistance(const char *a, const char *b) {
+  long dist;
+  int gota, gotb;
+  unsigned long h, p;
+  wint_t chara, charb;
+  dist = p = 0;
+  for (;;) {
+    gota = abs(tpdecode(a, &chara)); /* parses utf-8 multibyte characters */
+    gotb = abs(tpdecode(b, &charb)); /* abs() handles -1, always yields � */
+    if (!chara && !charb) break;
+    if (!chara || !charb) {
+      dist += MISSING_LETTER_DISTANCE;
+    } else if ((h = hamming(chara, charb))) {
+      dist += h + p++; /* penalize multiple mismatched letters */
+    }
+    if (chara) a += gota;
+    if (charb) b += gotb;
+  }
+  return dist;
+}
+
+intptr_t ConsiderWord(const char *word, void *arg) {
+  long dist;
+  if ((dist = WordDistance(word, query)) < MAX_NEARBY_WORD_DISTANCE) {
+    append(&nearby, &((struct WordMatch){dist, word}));
+  }
+  return 0;
+}
+
+int CompareWords(const struct WordMatch *a, const struct WordMatch *b) {
+  return a->dist < b->dist;
+}
+
+void FindNearbyWords(void) {
+  nearby.i = 0;
+  critbit0_allprefixed(&words, "", ConsiderWord, NULL);
+  qsort(nearby.p, nearby.i, sizeof(struct WordMatch), (void *)CompareWords);
+}
+
+void SpellChecker(void) {
+  int i;
+  printf("@(#) Cosmopolitan Ispell Version 3.4.00 8 Feb 2015\r\n");
+  while (!feof(stdin)) {
+    printf("word: ");
+    fflush(stdout);
+    if (getline(&line, &linesize, stdin) > 0) {
+      query = strtolower(chomp(line));
+      if (critbit0_contains(&words, query)) {
+        printf("ok\r\n");
+      } else {
+        FindNearbyWords();
+        if (nearby.i) {
+          printf("how about: ");
+          for (i = 0; i < MIN(MAX_NEARBY_RESULTS, nearby.i); ++i) {
+            if (i) printf(", ");
+            fputs(nearby.p[i].word, stdout);
+          }
+          printf("\r\n");
+        } else {
+          printf("not found\r\n");
+        }
+      }
+    }
+    printf("\r\n");
+  }
+  CHECK_NE(-1, fclose(stdin));
+  CHECK_NE(-1, fclose(stdout));
+}
+
+void LoadWords(void) {
+  CHECK_NOTNULL((f = fopen("zip:usr/share/dict/words", "r")));
+  while (getline(&line, &linesize, f) > 0) {
+    critbit0_insert(&words, strtolower(chomp(line)));
+  }
+  CHECK_NE(-1, fclose(f));
+}
+
+int main(int argc, char *argv[]) {
+  showcrashreports();
+  LoadWords();
+  SpellChecker();
+  return 0;
+}
diff --git a/libc/bits/bits.h b/libc/bits/bits.h
index 68e01224..3a550e5c 100644
--- a/libc/bits/bits.h
+++ b/libc/bits/bits.h
@@ -36,6 +36,7 @@ uint64_t bitreverse64(uint64_t) libcesque pureconst;
 unsigned long roundup2pow(unsigned long) libcesque pureconst;
 unsigned long roundup2log(unsigned long) libcesque pureconst;
 unsigned long rounddown2pow(unsigned long) libcesque pureconst;
+unsigned long hamming(unsigned long, unsigned long) pureconst;
 
 /*───────────────────────────────────────────────────────────────────────────│─╗
 │ cosmopolitan § bits » no assembly required                               ─╬─│┼
diff --git a/libc/bits/hamming.c b/libc/bits/hamming.c
index 5f74b472..38beb33a 100644
--- a/libc/bits/hamming.c
+++ b/libc/bits/hamming.c
@@ -19,6 +19,9 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/bits/bits.h"
 
-unsigned long(hamming)(unsigned long x, unsigned long y) {
+/**
+ * Counts number of different bits.
+ */
+unsigned long hamming(unsigned long x, unsigned long y) {
   return popcount(x ^ y);
 }
diff --git a/test/libc/str/tpdecode_test.c b/test/libc/str/tpdecode_test.c
index 11c360eb..deb82cb6 100644
--- a/test/libc/str/tpdecode_test.c
+++ b/test/libc/str/tpdecode_test.c
@@ -30,6 +30,12 @@
 
 wint_t wc;
 
+TEST(tpdecode, testEmptyString_consumesNulTerminator) {
+  wc = 123;
+  EXPECT_EQ(1, tpdecode("", &wc));
+  EXPECT_EQ(0, wc);
+}
+
 TEST(tpdecode, testGlyph) {
   EXPECT_EQ(u'→', PROGN(ASSERT_EQ(3, tpdecode("→", &wc)), wc));
   EXPECT_EQ(L'𐌰', PROGN(ASSERT_EQ(4, tpdecode("𐌰𐌱𐌲𐌳", &wc)), wc));
diff --git a/usr/share/dict/words.gz b/usr/share/dict/words.gz
new file mode 100644
index 00000000..df125841
Binary files /dev/null and b/usr/share/dict/words.gz differ