Fix erg's ratio bug

core/math/parser/parser-tests.factor

@@ -108,3 +108,6 @@ unit-test
 [ -1.0/0.0 ] [ "-1/0." string>number ] unit-test
 
 [ "-0.0" ] [ -0.0 number>string ] unit-test
+
+[ "-3/4" ] [ -3/4 number>string ] unit-test
+[ "-1-1/4" ] [ -5/4 number>string ] unit-test

core/math/parser/parser.factor

@@ -105,7 +105,7 @@ GENERIC# >base 1 ( n radix -- str )
 
 <PRIVATE
 
-: (>base) ( n -- str ) radix get >base ;
+: (>base) ( n -- str ) radix get positive>base ;
 
 PRIVATE>
 
@@ -123,7 +123,7 @@ M: integer >base
 M: ratio >base
     [
         dup 0 < negative? set
-        1 /mod
+        abs 1 /mod
         [ dup zero? [ drop "" ] [ (>base) sign append ] if ]
         [
             [ numerator (>base) ]