diff --git a/hawk/README.md b/hawk/README.md
new file mode 100644
index 00000000..e897a463
--- /dev/null
+++ b/hawk/README.md
@@ -0,0 +1,66 @@
+# Hawk
+
+# Table of Contents
+- [Language](#language)
+- [Embedding Guide](#embedding-guide)
+
+#### TODO: unary bitwise not
+#### TODO: fix -F or --field-separator to hawk.
+
+
+## Language <a name="language"></a>
+
+Hawk implements most of the AWK programming language elements with extensions.
+
+
+### Entry Point
+
+You may change the entry point of your script by setting a function name with @pragma entry.
+
+<pre>
+@pragma entry main
+
+function main ()
+{
+	print "hello, world";
+}
+</pre>
+
+### Value
+
+- unitialized value
+- integer
+- floating-point number
+- string
+- byte string
+- array
+
+### Module
+
+
+
+### Incompatibility with AWK
+
+#### Parameter passing
+
+In AWK, the caller can pass an uninitialized variable as a function parameter and get a changed value if the callled function sets it to an array.
+
+<pre>
+function q(a) {a[1]=20; a[2]=30;}
+BEGIN { q(x); for (i in x) print i, x[i]; }
+</pre>
+
+In Hawk, you can prefix the pramater name with & to indicate call-by-reference for the same effect.
+<pre>
+function q(&a) {a[1]=20; a[2]=30;}
+BEGIN { q(x); for (i in x) print i, x[i]; }
+</pre>
+
+Alternatively, you may form an array before passing it to a function.
+<pre>
+function q(a) {a[1]=20; a[2]=30;}
+BEGIN { x[3]=99; q(x); for (i in x) print i, x[i]; }'
+</pre>
+
+
+## Embedding Guide <a name="embedding-guide"></a>
diff --git a/hawk/bin/main.c b/hawk/bin/main.c
index 9cc66fc8..018d8fb7 100644
--- a/hawk/bin/main.c
+++ b/hawk/bin/main.c
@@ -381,7 +381,7 @@ static int apply_fs_and_gvs_to_rtx (hawk_rtx_t* rtx, arg_t* arg)
 
 		/* compose a string value to use to set FS to */
 		fs = hawk_rtx_makestrvalwithbcstr(rtx, arg->fs);
-		if (fs) return -1;
+		if (!fs) return -1;
 
 		/* change FS according to the command line argument */
 		hawk_rtx_refupval (rtx, fs);