Make use of \u2190 char optional

VS2010 is not capable of compiling source code with chars beyond the
"current code page" reliably.

peglib.h

@@ -35,6 +35,10 @@
 #endif
 #endif
 
+// define if the compiler doesn't support unicode characters reliably in the
+// source code
+//#define PEGLIB_NO_UNICODE_CHARS
+
 namespace peg {
 
 extern void* enabler;
@@ -1813,7 +1817,11 @@ private:
                                seq(lit("\\x"), cls("0-9a-fA-F"), opt(cls("0-9a-fA-F"))),
                                seq(npd(chr('\\')), dot()));
 
+#if !defined(PEGLIB_NO_UNICODE_CHARS)
         g["LEFTARROW"]  <= seq(cho(lit("<-"), lit("←")), g["Spacing"]);
+#else
+        g["LEFTARROW"]  <= seq(lit("<-"), g["Spacing"]);
+#endif
         ~g["SLASH"]     <= seq(chr('/'), g["Spacing"]);
         g["AND"]        <= seq(chr('&'), g["Spacing"]);
         g["NOT"]        <= seq(chr('!'), g["Spacing"]);

test/test.cc

@@ -5,7 +5,8 @@
 #include <peglib.h>
 #include <iostream>
 
-TEST_CASE("Simple syntax test", "[general]")
+#if !defined(PEGLIB_NO_UNICODE_CHARS)
+TEST_CASE("Simple syntax test (with unicode)", "[general]")
 {
     peg::parser parser(
         " ROOT ← _ "
@@ -15,6 +16,18 @@ TEST_CASE("Simple syntax test", "[general]")
     bool ret = parser;
     REQUIRE(ret == true);
 }
+#endif
+
+TEST_CASE("Simple syntax test", "[general]")
+{
+    peg::parser parser(
+        " ROOT <- _ "
+        " _ <- ' ' "
+    );
+
+    bool ret = parser;
+    REQUIRE(ret == true);
+}
 
 TEST_CASE("Empty syntax test", "[general]")
 {