diff --git a/README.md b/README.md
index df9c44d..c03c371 100644
--- a/README.md
+++ b/README.md
@@ -16,12 +16,37 @@ $ git clone git://github.com/spencertipping/bash-lambda
 $ source bash-lambda/bash-lambda
 ```
 
+*Before you do this, be aware that bash-lambda garbage-collects a part of your
+filesystem. Think about what might theoretically go wrong with this.* I source
+it in my .bashrc without problems, but as always, your mileage may vary.
+
+Sourcing `bash-lambda` will do a few things:
+
+1. Create a heap directory in `$TMPDIR` (usually `/tmp`)
+2. Add this heap directory to your `$PATH`
+3. Add the asynchronous GC hook to your `$PROMPT_COMMAND`
+4. Add lots of variables and functions to your shell process
+5. Add an `EXIT` trap to nuke the heap directory
+
 Loading the library takes very little time even though a new heap is created
 for every process. This is because the heap setup and sourcing of your
 `.bash-lambda` file (run `defs` to edit it) is all done asynchronously. When
 the background initialization is complete, a small `λ` will appear in the
 rightmost column of your window.
 
+You can write arbitrary text to the right-hand side of the terminal by using
+the `message` function:
+
+```
+$ message hi
+$                                             hi
+```
+
+Before getting started, go ahead and run `defs` once. This will initialize your
+`~/.bash-lambda` file with some useful functions for common file operations. If
+you already have a `~/.bash-lambda` file from an earlier version, you can stash
+it somewhere, run `defs`, and then merge in previous definitions.
+
 ## Defining functions
 
 The functions provided by bash-lambda take their nomenclature from Clojure, and
@@ -177,6 +202,15 @@ $ seq 1 4 | reductions $add 0
 $
 ```
 
+Filtering is useful when working with files, especially in conjunction with
+some builtins that come with the standard `~/.bash-lambda` file. For example:
+
+```
+$ ls | filter is-d      # same as ls | filter $(fn '[[ -d $1 ]]')
+src
+$ ls | filter $(newerthan build)
+```
+
 ### Flatmap (mapcat in Clojure)
 
 It turns out that `map` already does what you need to write `mapcat`. The lists
@@ -364,6 +398,29 @@ $
 The exit code is also memoized; however, standard error and other side-effects
 are not. There is no way to clear a future after it has finished executing.
 
+### Mapping
+
+You can use the `future_map` function to transform the output of a future when
+it completes. You can also use this to trigger alerts. For example:
+
+```
+$ f=$(future $(fn 'sleep 10'))
+$ future_map $f $(fn 'message done')
+$
+```
+
+If you do this, the word 'done' will show up on the right side of the terminal
+in a few seconds.
+
+Command output is usually captured by the future. The only reason `message`
+works is that it prints to standard error, which is let through synchronously.
+This way you can immediately observe failures in future processes.
+
+Note that `future_map` is not a multimethod. The reason is that the regular
+`map` function needs to be able to process stdin, which has no `ref_type`. As a
+result, `map` is not a multimethod, so by extension, `future_map` is not an
+implementation of `map`.
+
 ### Partial results
 
 You can use `unsafe_get` to retrieve whatever stdout has been produced without
diff --git a/bash-lambda b/bash-lambda
index 07d611f..164a432 100755
--- a/bash-lambda
+++ b/bash-lambda
@@ -5,6 +5,7 @@
 # functions in the shell. The heap will be deleted automatically when the shell
 # exits. See https://github.com/spencertipping/bash-lambda for documentation.
 
+#!/bin/bash
 # Bash-lambda disk-based heap
 
 # We need 128 bits of entropy for the heap directory name. This gives us
@@ -56,7 +57,7 @@ bash_lambda_cons() {
   cat > $(bash_lambda_gc_guard "$file") &&      # Take everything from stdin
     chmod u+x "$file"                   &&      # All conses are executable
     echo "$file"; }
-
+#!/bin/bash
 # Bash-lambda reference functions
 
 bash_lambda_ref() {
@@ -129,7 +130,7 @@ bash_lambda_ref_children() {
 
   egrep -o "$BASH_LAMBDA_HEAP/[^ [:space:]/\)\}\"']+" | (declare ref
     while read ref; do [[ -e "$ref" ]] && echo "$ref"; done); }
-
+#!/bin/bash
 # Bash-lambda concurrent mark-sweep garbage collector
 
 # BASH_LAMBDA_GC_SECONDS=0 will disable automatic GC
@@ -233,7 +234,7 @@ bash_lambda_gc_unpin() { rm -f "$BASH_LAMBDA_HEAP/.gc-permanent/${1##*/}";
 bash_lambda_gc_roots() {
   declare; ps ax; ls -d "$BASH_LAMBDA_HEAP/.gc-permanent"/* | (declare x
     while read x; do echo "$BASH_LAMBDA_HEAP/${x##*/}"; done); }
-
+#!/bin/bash
 # Bash-lambda function and closure allocation
 
 bash_lambda_fn_body() {
@@ -265,14 +266,12 @@ bash_lambda_defn() { declare name=$1; shift
 # pinned so that they will never be garbage-collected.
 bash_lambda_extern() {
   bash_lambda_gc_pin $( (echo "#!/bin/bash"
-                         echo "$1_main() {"
-                         declare -f "$1" | grep '^  '
-                         echo "}"
-                         echo "$1_main \"\$@\"") | bash_lambda_cons -n $1); }
+                         declare -f "$1"
+                         echo "$1 \"\$@\"") | bash_lambda_cons -n $1); }
 
 bash_lambda_def() { rm -f $BASH_LAMBDA_HEAP/$1
                     ln -s $2 $(bash_lambda_gc_pin $BASH_LAMBDA_HEAP/$1); }
-
+#!/bin/bash
 # Bash-lambda functional programming constructs
 
 # $(comp $f $g $h) x = f $(g $(h x))
@@ -287,7 +286,7 @@ bash_lambda_comp() {
 
 bash_lambda_partial() {
   bash_lambda_fn "$* \"\$@\""; }
-
+#!/bin/bash
 # Bash-lambda multimethods
 
 # These work only on fully-named parameters, not on stuff coming from stdin. If
@@ -324,7 +323,7 @@ bash_lambda_defmulti() {
                count \
                grab release wrap; do
    bash_lambda_defmulti $method; done) > /dev/null
-
+#!/bin/bash
 # Bash-lambda pipe locks
 
 # A pipe-lock is a way to block one process until another one lets it through.
@@ -343,7 +342,7 @@ bash_lambda_pipelock() {
 
 bash_lambda_pipelock_grab()    { cat $1 >& /dev/null; }
 bash_lambda_pipelock_release() { echo > $1; }
-
+#!/bin/bash
 # Bash-lambda semaphores and mutexes
 
 # Semaphores are directories that contain empty numbered subdirectories along
@@ -400,7 +399,7 @@ bash_lambda_mutex_wrap() {
                     declare status=\$?
                     bash_lambda_mutex_release \$lock
                     exit \$status; fi"; }
-
+#!/bin/bash
 # Bash-lambda atomic values
 
 # An atomic value supports thread-safe assignment and access. It does this by
@@ -439,7 +438,7 @@ bash_lambda_atom_wrap() {
                     declare status=\$?
                     bash_lambda_atom_release \$lock
                     exit \$status; fi"; }
-
+#!/bin/bash
 # Bash-lambda list programming constructs
 
 bash_lambda_list() { declare x
@@ -496,7 +495,7 @@ bash_lambda_every() {
   cat ${2:--} | (declare x; while read x; do
                   if ! $1 "$x" > /dev/null; then
                     echo "$x"; return 1; fi; done; return 0); }
-
+#!/bin/bash
 # Bash-lambda futures (asynchronous processes)
 
 # Future locking
@@ -519,7 +518,7 @@ bash_lambda_future() {
   declare result=$(printf $"%s\n%s\n%s\n" $output $status $state | \
                    bash_lambda_cons future)
 
-  ("$@" > $output; echo $? > $status; notify $result) >& /dev/null &
+  ("$@" > $output; echo $? > $status; notify $result) > /dev/null &
   echo $result; }
 
 bash_lambda_future_finished() {
@@ -551,6 +550,10 @@ bash_lambda_future_get() {
   cat "$(bash_lambda_nth 0 "$1")"
   return "$(< "$(bash_lambda_nth 1 "$1")")"; }
 
+bash_lambda_future_map() {
+  # Returns a future of a function applied to this future's value.
+  bash_lambda_future $(fn "$2 \$(future_get $1)"); }
+
 bash_lambda_future_unsafe_get() {
   # Gets whatever stdout has been produced so far. The process may not have
   # exited, so this function returns 0.
@@ -559,7 +562,7 @@ bash_lambda_future_unsafe_get() {
 bash_lambda_future_transpose() {
   bash_lambda_future $(bash_lambda_partial \
     bash_lambda_map bash_lambda_future_get $1); }
-
+#!/bin/bash
 # Bash-lambda remote functions
 
 # Remote functions allow you to transparently migrate the execution of a
@@ -594,7 +597,7 @@ bash_lambda_remote() {
 bash_lambda_remote_clean() {
   # Removes this instance's heap snapshot from the remote instance.
   ssh $host "rm -rf \"$BASH_LAMBDA_HEAP\""; }
-
+#!/bin/bash
 # Bash-lambda wait functions
 
 # Various ways to wait for things. Usually you would use this with semaphores,
@@ -626,7 +629,7 @@ bash_lambda_spin_until() { $(bash_lambda_spinning_fn "$@"); }
 
 bash_lambda_wait_wrap() { $(wait_until $(bash_lambda_partial wrap "$@")); }
 bash_lambda_spin_wrap() { $(spin_until $(bash_lambda_partial wrap "$@")); }
-
+#!/bin/bash
 # Bash-lambda parallel execution
 
 # Parallel tasks are defined as an interface that transposes parallelism over
@@ -663,37 +666,48 @@ bash_lambda_parallel_map() {
                         $(bash_lambda_semaphore_wrap $s $f))
 
   bash_lambda_map $(bash_lambda_partial bash_lambda_future $blocking_f) $xs; }
-
+#!/bin/bash
 # Bash-lambda rc file functions
 
 export BASH_LAMBDA_RC=${BASH_LAMBDA_RC:-$HOME/.bash-lambda}
 export BASH_LAMBDA_EDITOR=${BASH_LAMBDA_EDITOR:-${EDITOR:-$VISUAL}}
 
+export COLUMNS  # so that bash_lambda_message can be called from subshells
+
 bash_lambda_message() {
   declare m="$*"
-  (( $COLUMNS )) && echo -en "\033[s\033[$((COLUMNS - ${#m}))G$m\033[u"; }
+  (( $COLUMNS )) && echo -en "\033[s\033[$((COLUMNS - ${#m}))G$m\033[u" 1>&2; }
 
 bash_lambda_setup_rc() {
-  [[ -e "$BASH_LAMBDA_RC" ]] || sed 's/^  //' > "$BASH_LAMBDA_RC" \
-  <<<"#!/bin/bash
-  # You can put function defs here. Variables you define here aren't visible,
-  # since this file is always evaluated (usually asynchronously) from inside a
-  # subshell.
-  #
-  # This file is sourced asynchronously when you start your shell, so adding
-  # definitions won't increase the amount of time required to open a new
-  # terminal.
-  #
-  # See https://github.com/spencertipping/bash-lambda for details about
-  # defining functions.
-  #
-  # Examples:
-  #
-  # def my-computers \$(list host1 host2 host3)
-  # defn check-status 'hostname; df -h | grep  /$; uptime'
-  # defn check-computers 'map \$(partial remote check-status)'
-  #
-  "; }
+  [[ -e "$BASH_LAMBDA_RC" ]] || sed 's/^  //' > "$BASH_LAMBDA_RC" <<'EOF'
+#!/bin/bash
+# You can put function defs here. Variables you define here aren't visible,
+# since this file is always evaluated (usually asynchronously) from inside a
+# subshell.
+#
+# This file is sourced asynchronously when you start your shell, so adding
+# definitions won't increase the amount of time required to open a new
+# terminal.
+#
+# See https://github.com/spencertipping/bash-lambda for details about
+# defining functions.
+#
+# For example:
+
+# File tests (wrappers for -d, -x, etc)
+def  bash_tests $(ref $(list a b c d e f g h k p r s t u w x G L N O S z n))
+defn deffiletest x 'defn is-$x f "[[ -$x \$f ]]"'
+map deffiletest $(bash_tests)
+
+defn newerthan file 'bash_lambda_fn f "[[ \$f -nt $file ]]"'
+defn olderthan file 'bash_lambda_fn f "[[ \$f -ot $file ]]"'
+defn eq        file 'bash_lambda_fn f "[[ \$f -ef $file ]]"'
+
+# Content tests
+defn contains pattern 'egrep -o $pattern'
+defn without pattern  'sed "s/${pattern/\//\\\/}//g"'
+EOF
+}
 
 bash_lambda_reload_rc() {
   [[ -e "$BASH_LAMBDA_RC" ]] && (. "$BASH_LAMBDA_RC" > /dev/null); }
@@ -702,7 +716,7 @@ bash_lambda_defs() {
   bash_lambda_setup_rc
   $BASH_LAMBDA_EDITOR "$BASH_LAMBDA_RC"
   (bash_lambda_reload_rc &); }
-
+#!/bin/bash
 # Bash-lambda function exporting and GC hooks
 
 # Export the bash_lambda library into the current heap
@@ -720,4 +734,3 @@ bash_lambda_init() {
 
 # Run a GC, if necessary, after each command
 export PROMPT_COMMAND="$PROMPT_COMMAND; bash_lambda_auto_gc"
-
diff --git a/build b/build
index 7a46ff8..4c8d222 100755
--- a/build
+++ b/build
@@ -1,11 +1,6 @@
 #!/bin/bash
 (cat src/header
- for file in heap ref gc fn fp multi \
-             pipelock semaphore atom \
-             list \
-             future remote wait parallel \
-             rc init; do
-  cat src/$file | grep -v '^#!'
-  echo; done) > bash-lambda
+ cat src/{heap,ref,gc,fn,fp,multi,pipelock,semaphore,atom} \
+     src/{list,future,remote,wait,parallel,rc,init}) > bash-lambda
 
 chmod +x bash-lambda
diff --git a/src/fn b/src/fn
index dd12e08..d492ce8 100644
--- a/src/fn
+++ b/src/fn
@@ -30,10 +30,8 @@ bash_lambda_defn() { declare name=$1; shift
 # pinned so that they will never be garbage-collected.
 bash_lambda_extern() {
   bash_lambda_gc_pin $( (echo "#!/bin/bash"
-                         echo "$1_main() {"
-                         declare -f "$1" | grep '^  '
-                         echo "}"
-                         echo "$1_main \"\$@\"") | bash_lambda_cons -n $1); }
+                         declare -f "$1"
+                         echo "$1 \"\$@\"") | bash_lambda_cons -n $1); }
 
 bash_lambda_def() { rm -f $BASH_LAMBDA_HEAP/$1
                     ln -s $2 $(bash_lambda_gc_pin $BASH_LAMBDA_HEAP/$1); }
diff --git a/src/future b/src/future
index 9954f5c..95a22b6 100644
--- a/src/future
+++ b/src/future
@@ -21,7 +21,7 @@ bash_lambda_future() {
   declare result=$(printf $"%s\n%s\n%s\n" $output $status $state | \
                    bash_lambda_cons future)
 
-  ("$@" > $output; echo $? > $status; notify $result) >& /dev/null &
+  ("$@" > $output; echo $? > $status; notify $result) > /dev/null &
   echo $result; }
 
 bash_lambda_future_finished() {
@@ -53,6 +53,10 @@ bash_lambda_future_get() {
   cat "$(bash_lambda_nth 0 "$1")"
   return "$(< "$(bash_lambda_nth 1 "$1")")"; }
 
+bash_lambda_future_map() {
+  # Returns a future of a function applied to this future's value.
+  bash_lambda_future $(fn "$2 \$(future_get $1)"); }
+
 bash_lambda_future_unsafe_get() {
   # Gets whatever stdout has been produced so far. The process may not have
   # exited, so this function returns 0.
diff --git a/src/rc b/src/rc
index 48f7f69..7a9864e 100644
--- a/src/rc
+++ b/src/rc
@@ -4,31 +4,42 @@
 export BASH_LAMBDA_RC=${BASH_LAMBDA_RC:-$HOME/.bash-lambda}
 export BASH_LAMBDA_EDITOR=${BASH_LAMBDA_EDITOR:-${EDITOR:-$VISUAL}}
 
+export COLUMNS  # so that bash_lambda_message can be called from subshells
+
 bash_lambda_message() {
   declare m="$*"
-  (( $COLUMNS )) && echo -en "\033[s\033[$((COLUMNS - ${#m}))G$m\033[u"; }
+  (( $COLUMNS )) && echo -en "\033[s\033[$((COLUMNS - ${#m}))G$m\033[u" 1>&2; }
 
 bash_lambda_setup_rc() {
-  [[ -e "$BASH_LAMBDA_RC" ]] || sed 's/^  //' > "$BASH_LAMBDA_RC" \
-  <<<"#!/bin/bash
-  # You can put function defs here. Variables you define here aren't visible,
-  # since this file is always evaluated (usually asynchronously) from inside a
-  # subshell.
-  #
-  # This file is sourced asynchronously when you start your shell, so adding
-  # definitions won't increase the amount of time required to open a new
-  # terminal.
-  #
-  # See https://github.com/spencertipping/bash-lambda for details about
-  # defining functions.
-  #
-  # Examples:
-  #
-  # def my-computers \$(list host1 host2 host3)
-  # defn check-status 'hostname; df -h | grep  /$; uptime'
-  # defn check-computers 'map \$(partial remote check-status)'
-  #
-  "; }
+  [[ -e "$BASH_LAMBDA_RC" ]] || sed 's/^  //' > "$BASH_LAMBDA_RC" <<'EOF'
+#!/bin/bash
+# You can put function defs here. Variables you define here aren't visible,
+# since this file is always evaluated (usually asynchronously) from inside a
+# subshell.
+#
+# This file is sourced asynchronously when you start your shell, so adding
+# definitions won't increase the amount of time required to open a new
+# terminal.
+#
+# See https://github.com/spencertipping/bash-lambda for details about
+# defining functions.
+#
+# For example:
+
+# File tests (wrappers for -d, -x, etc)
+def  bash_tests $(ref $(list a b c d e f g h k p r s t u w x G L N O S z n))
+defn deffiletest x 'defn is-$x f "[[ -$x \$f ]]"'
+map deffiletest $(bash_tests)
+
+defn newerthan file 'bash_lambda_fn f "[[ \$f -nt $file ]]"'
+defn olderthan file 'bash_lambda_fn f "[[ \$f -ot $file ]]"'
+defn eq        file 'bash_lambda_fn f "[[ \$f -ef $file ]]"'
+
+# Content tests
+defn contains pattern 'egrep -o $pattern'
+defn without pattern  'sed "s/${pattern/\//\\\/}//g"'
+EOF
+}
 
 bash_lambda_reload_rc() {
   [[ -e "$BASH_LAMBDA_RC" ]] && (. "$BASH_LAMBDA_RC" > /dev/null); }