diff --git a/src/fun.sh b/src/fun.sh
index e1ad6d9..5d44542 100755
--- a/src/fun.sh
+++ b/src/fun.sh
@@ -398,3 +398,40 @@ maybevalue() {
   fi
 }
 
+
+# commonly used predicates for filter
+# e.g.  list 1 a 2 b 3 c | filter lambda x . 'isint $x'
+
+# inverse another test, e.g. "not isint $x"
+not() {
+  local r=$("$@" 2>/dev/null)
+  $r && ret false || ret true
+}
+
+isint() {
+  [ "$1" -eq "$1" ] 2>/dev/null && ret true || ret false
+}
+
+isempty() {
+  [ -z "$1" ] && ret true || ret false
+}
+
+isfile() {
+  [ -f "$1" ] && ret true || ret false
+}
+
+isnonzerofile() {
+  [ -s "$1" ] && ret true || ret false
+}
+
+isreadable() {
+  [ -r "$1" ] && ret true || ret false
+}
+
+iswritable() {
+  [ -w "$1" ] && ret true || ret false
+}
+
+isdir() {
+  [ -d "$1" ] && ret true || ret false
+}
diff --git a/test/predicates_test.sh b/test/predicates_test.sh
new file mode 100755
index 0000000..79bff20
--- /dev/null
+++ b/test/predicates_test.sh
@@ -0,0 +1,52 @@
+#! /bin/bash
+
+testIsint() {
+  assertEquals 'true' $(isint 1)
+  assertEquals 'true' $(isint -1)
+  assertEquals 'false' $(isint a)
+  assertEquals 'false' $(isint "")
+  assertEquals '1 2 3 4 5' "$(list 1 a 2 b 3 c 4 d 5 e | filter lambda x . 'isint $x' | unlist )"
+  assertEquals '1 2'       "$(list 1 a 2 b 3 c 4 d 5 e | filter lambda x . '($(isint $x) &&  [[ $x -le 2 ]] && ret true) || ret false ' | unlist )"
+
+  assertEquals 'false' $(not isint 1)
+  assertEquals 'true' $(not isint a)
+}
+
+testIsempty() {
+  assertEquals 'true' $(isempty "")
+  assertEquals 'false' $(isempty a)
+
+  assertEquals 'true' $(not isempty a)
+  assertEquals 'false' $(not isempty "")
+}
+
+testIsfile() {
+  f=$(mktemp)
+
+  assertEquals 'true' $(isfile $f)
+  assertEquals 'false' $(isfile $f.xxx)
+  assertEquals 'false' $(isfile "")
+  assertEquals 'true' $(not isfile $f.xxx)
+
+  assertEquals 'false' $(isnonzerofile $f)
+  echo hello world >$f
+  assertEquals 'true' $(isnonzerofile $f)
+
+  assertEquals 'true' $(iswritable $f)
+  chmod 400 $f
+  assertEquals 'false' $(iswritable $f)
+
+  assertEquals 'true' $(isreadable $f)
+  chmod 200 $f
+  assertEquals 'false' $(isreadable $f)
+
+  chmod 600 $f
+  rm $f
+}
+
+testIsdir() {
+  assertEquals 'true' $(isdir .)
+  assertEquals 'false' $(isdir sir_not_appearing_in_this_film)
+}
+
+. ./shunit2-init.sh