extra: using empty? in some places.

extra/benchmark/tcp-echo0/tcp-echo0.factor

@@ -46,7 +46,7 @@ M: tcp-echo handle-client*
     <tcp-echo> [
         \ threaded-server get server>address binary [
             #times [ #bytes read-write ] times
-            contents length 0 = [ incorrect-#bytes ] unless
+            contents empty? [ incorrect-#bytes ] unless
         ] with-client
     ] with-threaded-server ;
 

extra/fuel/xref/xref.factor

@@ -31,7 +31,7 @@ IN: fuel.xref
     >alist natural-sort ;
 
 : filter-prefix ( seq prefix -- seq )
-    [ drop-prefix nip length 0 = ] curry filter members ;
+    [ drop-prefix nip empty? ] curry filter members ;
 
 MEMO: (vocab-words) ( name -- seq )
     >vocab-link words [ name>> ] map ;

extra/math/text/english/english.factor

@@ -65,12 +65,10 @@ SYMBOL: and-needed?
     [ " " glue ] unless-empty ;
 
 : append-with-conjunction ( str1 str2 -- newstr )
-    over length 0 = [
-        nip
-    ] [
-        swap and-needed? get " and " ", " ?
-        glue and-needed? off
-    ] if ;
+    swap [
+        and-needed? get " and " ", " ? glue
+        and-needed? off
+    ] unless-empty ;
 
 : (recombine) ( str index seq -- newstr )
     2dup nth 0 = [

extra/mongodb/driver/driver.factor

@@ -149,7 +149,7 @@ M: mdb-collection create-collection ( collection -- )
     over '[ [ ] [ name>> ] bi _ set-at ] each ;
 
 : ensure-collection-map ( mdb-instance -- assoc )
-    dup collections>> dup keys length 0 = 
+    dup collections>> dup assoc-empty?
     [ drop build-collection-map [ >>collections drop ] keep ]
     [ nip ] if ;