diff --git a/.version b/.version
index 879b416..f9fe6b4 100644
--- a/.version
+++ b/.version
@@ -1 +1 @@
-2.1
+2.5b
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..cf8e84f
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,22 @@
+MIT License
+
+Copyright (c) 2020 Brandon Rozek
+Copyright (c) 2019 Sławomir Śledź
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
index 03d5783..15673cd 100644
--- a/README.md
+++ b/README.md
@@ -1,12 +1,15 @@
 # Introduction
 
-[Introduction to fun.sh library](http://ssledz.github.io/presentations/bash-fun.html#/)
+This is a fork of [ssledz's fun.sh library](https://github.com/ssledz/bash-fun).
 
+This is mainly for my own personal use cases. So I would recommend using ssledz's version instead.
+I mainly worked towards getting this library to mostly pass shellcheck, removed some functionality,
+and name deconflicted some of the functions with what I had in my system.
 # Quick start
 
 ```bash
 #!/bin/bash
-. <(test -e fun.sh || curl -Ls https://raw.githubusercontent.com/ssledz/bash-fun/master/src/fun.sh > fun.sh; cat fun.sh)
+. <(test -e fun.sh || curl -Ls https://raw.githubusercontent.com/brandon-rozek/bash-fun/master/src/fun.sh > fun.sh; cat fun.sh)
 
 seq 1 4 | sum
 ```
@@ -14,13 +17,17 @@ seq 1 4 | sum
 # Functions overview
 |||||||
 |------|------|------|------|------|------|
-|**plus**|**append**|**buff**|**curry**|**div**|**drop**|
-|**factorial**|**filter**|**foldl**|**foldr**|**head**|**join**|
-|**lambda**|**last**|**list**|**map**|**mod**|**mul**|
-|**prepend**|**product**|**ret**|**revers_str**|**revers**|**scanl**|
-|**splitc**|**strip**|**sub**|**sum**|**tail**|**take**|
-|**catch**|**try**|**tupl**|**tupr**|**tup**|**tupx**|
-|**unlist**|**zip**|**λ**|**with_trampoline**|**res**|**call**|
+|**list_append**|**divide**|**take_while**|
+|**list_drop**|**drop_while**|**factorial**|**filter**|**foldl**|
+|**isint**|**isempty**|**isfile**|**isnonzerofile**|**isreadable**|**iswritable**|
+|**isdir**|**list_join**|**lambda**|**list_last**|**list_head**|**list**|
+|**list_tail**|**list_zip**|**list_map**|
+|**mod**|**multiply**|**not**|
+|**add**|**list_prepend**|**product**|**ret**|
+|**revers**|**revers_str**|**scanl**|**splitc**|**strip**|
+|**stripl**|**stripr**|**subtract**|**sum**|**take**|
+|**tup**|**unlist**|**λ**|
+
 
 ## *list/unlist*
 
@@ -34,25 +41,25 @@ $ list 1 2 3 4 5 | unlist
 1 2 3 4 5
 ```
 
-## *take/drop/tail/head/last*
+## *list_take/list_drop/list_tail/list_head/list_last*
 
 ```bash
-$ list 1 2 3 4 | drop 2
+$ list 1 2 3 4 | list_drop 2
 3
 4
 
-$ list 1 2 3 4 5 | head
+$ list 1 2 3 4 5 | list_head
 1
 
-$ list 1 2 3 4 | tail
+$ list 1 2 3 4 | list_tail
 2
 3
 4
 
-$ list 1 2 3 4 5 | last
+$ list 1 2 3 4 5 | list_last
 5
 
-$ list 1 2 3 4 5 | take 2
+$ list 1 2 3 4 5 | list_take 2
 1
 2
 ```
@@ -60,45 +67,36 @@ $ list 1 2 3 4 5 | take 2
 ## *join*
 
 ```bash
-$ list 1 2 3 4 5 | join ,
+$ list 1 2 3 4 5 | list_join ,
 1,2,3,4,5
-
-$ list 1 2 3 4 5 | join , [ ]
-[1,2,3,4,5]
 ```
 
 ## *map*
 
 ```bash
-$ seq 1 5 | map λ a . 'echo $((a + 5))'
+$ seq 1 5 | list_map λ a . 'echo $((a + 5))'
 6
 7
 8
 9
 10
 
-$ list a b s d e | map λ a . 'echo $a$(echo $a | tr a-z A-Z)'
+$ list a b s d e | list_map λ a . 'echo $a$(echo $a | tr a-z A-Z)'
 aA
 bB
 sS
 dD
 eE
+
+$ list 1 2 3 | list_map tee
+1
+2
+3
 ```
-
-## *flat map*
-
-```bash
-$ seq 2 3 | map λ a . 'seq 1 $a' | join , [ ]
-[1,2,1,2,3]
-
-$ list a b c | map λ a . 'echo $a; echo $a | tr a-z A-z' | join , [ ]
-[a,A,b,B,c,C]
-```
-
 ## *filter*
 
 ```bash
-$ seq 1 10 | filter λ a . '[[ $(mod $a 2) -eq 0 ]] && ret true || ret false'
+$ seq 1 10 | filter even
 2
 4
 6
@@ -111,10 +109,6 @@ $ seq 1 10 | filter λ a . '[[ $(mod $a 2) -eq 0 ]] && ret true || ret false'
 ```bash
 $ list a b c d | foldl λ acc el . 'echo -n $acc-$el'
 a-b-c-d
-
-$ list '' a b c d | foldr λ acc el .\
-    'if [[ ! -z $acc ]]; then echo -n $acc-$el; else echo -n $el; fi'
-d-c-b-a
 ```
 
 ```bash
@@ -123,11 +117,8 @@ $ seq 1 4 | foldl λ acc el . 'echo $(($acc + $el))'
 ```
 
 ```bash
-$ seq 1 4 | foldl λ acc el . 'echo $(mul $(($acc + 1)) $el)'
+$ seq 1 4 | foldl λ acc el . 'echo $(multiply $(($acc + 1)) $el)'
 64 # 1 + (1 + 1) * 2 + (4 + 1) * 3 + (15 + 1) * 4 = 64
-
-$ seq 1 4 | foldr λ acc el . 'echo $(mul $(($acc + 1)) $el)'
-56 # 1 + (1 + 1) * 4 + (8 + 1) * 3 + (27 + 1) * 2 = 56
 ```
 
 ## *tup/tupx/tupl/tupr*
@@ -140,19 +131,16 @@ $ tup 'foo bar' 1 'one' 2
 (foo bar,1,one,2)
 
 $ tup , 1 3
-(u002c,1,3)
+(,,1,3)
 ```
 
 ```bash
-$ tupl $(tup a 1)
+$ echo tup a 1 | tupl
 a
 
-$ tupr $(tup a 1)
+$ echo tup a 1 | tupr
 1
 
-$ tup , 1 3 | tupl
-,
-
 $ tup 'foo bar' 1 'one' 2 | tupl
 foo bar
 
@@ -160,39 +148,10 @@ $ tup 'foo bar' 1 'one' 2 | tupr
 2
 ```
 
-```bash
-$ tup 'foo bar' 1 'one' 2 | tupx 2
-1
-
-$ tup 'foo bar' 1 'one' 2 | tupx 1,3
-foo bar
-one
-
-$ tup 'foo bar' 1 'one' 2 | tupx 2-4
-1
-one
-2
-```
-
-## *buff*
+## *list_zip*
 
 ```bash
-$ seq 1 10 | buff λ a b . 'echo $(($a + $b))'
-3
-7
-11
-15
-19
-
-$ seq 1 10 | buff λ a b c d e . 'echo $(($a + $b + $c + $d + $e))'
-15
-40
-```
-
-## *zip*
-
-```bash
-$ list a b c d e f | zip $(seq 1 10)
+$ list a b c d e f | list_zip $(seq 1 10)
 (a,1)
 (b,2)
 (c,3)
@@ -202,60 +161,77 @@ $ list a b c d e f | zip $(seq 1 10)
 ```
 
 ```bash
-$ list a b c d e f | zip $(seq 1 10) | last | tupr
+$ list a b c d e f | list_zip $(seq 1 10) | list_last | tupr
 6
 ```
 
-## *curry*
+## *not/isint/isempty*
 
 ```bash
-add2() {
-    echo $(($1 + $2))
-}
-```
+$ isint 42
+true
 
-```bash
-$ curry inc add2 1
-```
+$ list blah | isint
+false
 
-```bash
-$ inc 2
-3
+$ not true
+false
 
-$ seq 1 3 | map λ a . 'inc $a'
-2
-3
-4
-```
+$ not "isint 777"
+false
 
-## *try/catch*
-
-```bash
-$ echo 'expr 2 / 0' | try λ _ . 'echo 0'
-0
-
-$ echo 'expr 2 / 0' | try λ status . 'echo $status'
-2
-
-$ echo 'expr 2 / 2' | try λ _ . 'echo 0'
+$ list 1 2 "" c d 6 | filter λ a . 'isint $a'
 1
-```
+2
+6
 
-```bash
-try λ  _ . 'echo some errors during pull; exit 1' < <(echo git pull)
-```
-
-```bash
-$ echo 'expr 2 / 0' \
-    | LANG=en catch λ cmd status val . 'echo cmd=$cmd,status=$status,val=$val'
-cmd=expr 2 / 0,status=2,val=(expr:,division,by,zero)
-```
-
-```bash
-$ echo 'expr 2 / 2' | catch λ _ _ val . 'tupl $val'
+$ list 1 2 "" c d 6 | filter λ a . 'not "isempty $a"'
 1
+2
+c
+d
+6
 ```
 
+## *isfile/isnonzerofile/isreadable/iswritable/isdir*
+
+```bash
+$ touch /tmp/foo
+
+$ isfile /tmp/foo
+true
+
+$ not iswritable /
+true
+
+$ files="/etc/passwd /etc/sudoers /tmp /tmp/foo /no_such_file"
+
+$ list $files | filter λ a . 'isfile $a'
+/etc/passwd
+/etc/sudoers
+/tmp/foo
+
+$ list $files | filter λ a . 'isdir $a'
+/tmp
+
+$ list $files | filter λ a . 'isreadable $a'
+/etc/passwd
+/tmp
+/tmp/foo
+
+$ list $files | filter λ a . 'iswritable $a'
+/tmp
+/tmp/foo
+
+$ list $files | filter λ a . 'isnonzerofile $a'
+/etc/passwd
+/etc/sudoers
+/tmp
+
+$ list $files | filter λ a . 'not isfile $a'
+/tmp
+/no_such_file
+```
 ## *scanl*
 
 ```bash
@@ -268,58 +244,10 @@ $ seq 1 5 | scanl lambda acc el . 'echo $(($acc + $el))'
 ```
 
 ```bash
-$ seq 1 5 | scanl lambda a b . 'echo $(($a + $b))' | last
+$ seq 1 5 | scanl lambda a b . 'echo $(($a + $b))' | list_last
 15
 ```
 
-## *with_trampoline/res/call*
-
-```bash
-factorial() {
-    fact_iter() {
-        local product=$1
-        local counter=$2
-        local max_count=$3
-        if [[ $counter -gt $max_count ]]; then
-            res $product
-        else
-            call fact_iter $(echo $counter\*$product | bc) $(($counter + 1)) $max_count
-        fi
-    }
-
-    with_trampoline fact_iter 1 1 $1
-}
-```
-
-```bash
-$ time factorial 30 | fold -w 70
-265252859812191058636308480000000
-
-real    0m1.854s
-user    0m0.072s
-sys     0m0.368s
-```
-
-```bash
-time factorial 60 | fold -w 70
-8320987112741390144276341183223364380754172606361245952449277696409600
-000000000000
-
-real    0m3.635s
-user    0m0.148s
-sys     0m0.692s
-```
-
-```bash
-$ time factorial 90 | fold -w 70
-1485715964481761497309522733620825737885569961284688766942216863704985
-393094065876545992131370884059645617234469978112000000000000000000000
-
-real    0m4.371s
-user    0m0.108s
-sys     0m0.436s
-```
-
 # Examples
 
 ```bash
@@ -332,7 +260,7 @@ processNames() {
 
   list $@ \
     | filter λ name . '[[ ${#name} -gt 1 ]] && ret true || ret false' \
-    | map λ name . 'uppercase $name' \
+    | list_map λ name . 'uppercase $name' \
     | foldl λ acc el . 'echo $acc,$el'
 
 }
@@ -344,7 +272,22 @@ processNames adam monika s slawek d daniel Bartek j k
 Adam,Monika,Slawek,Daniel,Bartek
 ```
 
+# Running tests
+TODO: Need to change the tests here
+```bash
+cd test
+./test_runner
+```
+
+# Contribution guidelines
+
+Feel free to ask questions in chat, open issues, or contribute by creating pull requests.
+
+In order to create a pull request
+* checkout master branch
+* introduce your changes & bump version
+* submit pull request
 
 # Resources
 * [Inspiration](https://quasimal.com/posts/2012-05-21-funsh.html)
-* [Functional Programming in Bash](https://medium.com/@joydeepubuntu/functional-programming-in-bash-145b6db336b7)
\ No newline at end of file
+* [Functional Programming in Bash](https://medium.com/@joydeepubuntu/functional-programming-in-bash-145b6db336b7)
diff --git a/examples/example.sh b/examples/example.sh
index 80cb792..c30c455 100755
--- a/examples/example.sh
+++ b/examples/example.sh
@@ -1,30 +1,29 @@
 #!/bin/bash
-
 source ../src/fun.sh
 
 seq 1 4 | sum
 seq 1 4 | product
 factorial 4
 seq 1 4 | scanl lambda a b . 'echo $(add $a $b)'
-echo map mul
-seq 1 4 | map lambda a . 'echo $(mul $a 2)'
-echo map sub
-seq 1 4 | map lambda a . 'echo $(sub $a 2)'
+echo map multiply
+seq 1 4 | list_map lambda a . 'echo $(multiply $a 2)'
+echo map minus
+seq 1 4 | list_map lambda a . 'echo $(minus $a 2)'
 echo map add
-seq 1 4 | map lambda a . 'echo $(add $a 2)'
-echo map div
-seq 1 4 | map lambda a . 'echo $(div $a 2)'
-echo map mod
-seq 1 4 | map lambda a . 'echo $(mod $a 2)'
+seq 1 4 | list_map lambda a . 'echo $(add $a 2)'
+echo map divide
+seq 1 4 | list_map lambda a . 'echo $(divide $a 2)'
+echo list_map mod
+seq 1 4 | list_map lambda a . 'echo $(mod $a 2)'
 echo 'list & head'
-list 1 2 3 4 5 | head
-list {1..2} | append {3..4} | prepend {99..102}
+list 1 2 3 4 5 | list_head
+list {1..2} | list_append {3..4} | list_prepend {99..102}
 list {1..2} | unlist
-list {1..10} | head
-list {1..10} | drop 7
-list {1..10} | take 3
-list {1..10} | last
-list {1..10} | map λ a . 'echo $(mul $a 2)'
+list {1..10} | list_head
+list {1..10} | list_drop 7
+list {1..10} | list_take 3
+list {1..10} | list_last
+list {1..10} | list_map λ a . 'echo $(multiply $a 2)'
 
 id() { 
   λ x . '$x' 
@@ -38,122 +37,32 @@ foobar() {
 
 list {1,2,3} | foobar
 
-echo -n abcdefg | revers_str                         # gfedcba
-echo -n abcdefg | splitc | join , '[' ']'            # [a,b,c,d,e,f,g]
-echo -n abcdefg | splitc | revers | join , '[' ']'   # [g,f,e,d,c,b,a]
+echo -n abcdefg | revers_str                # gfedcba
+echo -n abcdefg | splitc | list_join ,           # a,b,c,d,e,f,g
+echo -n abcdefg | splitc | revers | list_join ,  # g,f,e,d,c,b,a
 
-echo -n ' abcdefg' | splitc | foldr lambda a b . 'echo $a$b'  # gfedcba
-
-echo 'ls' | try λ cmd status ret . 'echo $cmd [$status]; echo $ret'
-
-list {1..10} | filter lambda a . '[[ $(mod $a 2) -eq 0 ]] && ret true || ret false' | join , '[' ']'  # [2,4,6,8,10]
-
-function add() {
-    expr $1 + $2
-}
-
-
-curry add3 add 3
-add3 9
+list {1..10} | filter lambda a . '[[ $(mod $a 2) -eq 0 ]] && ret true || ret false' | list_join ,  # 2,4,6,8,10
 
 list a b c d | foldl lambda acc el . 'echo -n $acc-$el'
-list '' a b c d | foldr lambda acc el . 'if [[ ! -z $acc ]]; then echo -n $acc-$el; else echo -n $el; fi'
-
 seq 1 4 | foldl lambda acc el . 'echo $(($acc + $el))'
 
 #1 - 2 - 3 - 4
 seq 1 4 | foldl lambda acc el . 'echo $(($acc - $el))'
-#1 - 4 - 3 - 2
-seq 1 4 | foldr lambda acc el . 'echo $(($acc - $el))'
 
 #1 + (1 + 1) * 2 + (4 + 1) * 3 + (15 + 1) * 4 = 64
-
-seq 1 4 | foldl lambda acc el . 'echo $(mul $(($acc + 1)) $el)'
-
-#1 + (1 + 1) * 4 + (8 + 1) * 3 + (27 + 1) * 2 = 56
-seq 1 4 | foldr lambda acc el . 'echo $(mul $(($acc + 1)) $el)'
+seq 1 4 | foldl lambda acc el . 'echo $(multiply $(($acc + 1)) $el)'
 
 tup a 1
-tupl $(tup a 1)
-tupr $(tup a 1)
 tup a 1 | tupl
 tup a 1 | tupr
 
-seq 1 10 | buff lambda a b . 'echo $(($a + $b))'
-echo 'XX'
-seq 1 10 | buff lambda a b c d e . 'echo $(($a + $b + $c + $d + $e))'
-
-list a b c d e f | zip $(seq 1 10)
+list a b c d e f | list_zip $(seq 1 10)
 
 echo
-list a b c d e f | zip $(seq 1 10) | last | tupr
-
-arg='[key1=value1,key2=value2,key3=value3]'
-get() {
-  local pidx=$1
-  local idx=$2
-  local arg=$3
-  echo $arg | tr -d '[]' | cut -d',' -f$idx | cut -d'=' -f$pidx
-}
-
-curry get_key get 1
-curry get_value get 2
-
-get_key 1 $arg
-get_value 1 $arg
-
-seq 1 3 | map lambda a . 'tup $(get_key $a $arg) $(get_value $a $arg)'
-
-echo 'ls /home' | try λ cmd status ret . 'echo $cmd [$status]; echo $ret'
-echo '/home' | try λ cmd status ret . 'echo $cmd [$status]; echo $ret'
+list a b c d e f | list_zip $(seq 1 10) | list_last | tupr
 
 seq 1 5 | scanl lambda a b . 'echo $(($a + $b))'
-seq 1 5 | scanl lambda a b . 'echo $(($a + $b))' | last
+seq 1 5 | scanl lambda a b . 'echo $(($a + $b))' | list_last
 
-seq 2 3 | map lambda a . 'seq 1 $a' | join , [ ]
-list a b c | map lambda a . 'echo $a; echo $a | tr a-z A-z' | join , [ ]
-
-echo 0 | cat - <(curl -s https://raw.githubusercontent.com/ssledz/bash-fun/v1.1.1/src/fun.sh) | \
-    map lambda a . 'list $a' | foldl lambda acc el . 'echo $(($acc + 1))'
-
-echo 0 | cat - <(curl -s curl -s https://raw.githubusercontent.com/ssledz/bash-fun/v1.1.1/src/fun.sh) \
-            | foldl lambda acc el . 'echo $(($acc + 1))'
-
-
-factorial() {
-    fact_iter() {
-        local product=$1
-        local counter=$2
-        local max_count=$3
-        if [[ $counter -gt $max_count ]]; then
-            echo $product
-        else
-            fact_iter $(echo $counter\*$product | bc) $(($counter + 1)) $max_count
-        fi
-    }
-
-    fact_iter 1 1 $1
-}
-
-factorial_trampoline() {
-    fact_iter() {
-        local product=$1
-        local counter=$2
-        local max_count=$3
-        if [[ $counter -gt $max_count ]]; then
-            res $product
-        else
-            call fact_iter $(echo $counter\*$product | bc) $(($counter + 1)) $max_count
-        fi
-    }
-
-    with_trampoline fact_iter 1 1 $1
-}
-
-echo Factorial test
-
-time factorial 30
-time factorial_trampoline 30
-
-time factorial 60
-time factorial_trampoline 60
\ No newline at end of file
+seq 2 3 | list_map lambda a . 'seq 1 $a' | list_join ,
+list a b c | list_map lambda a . 'echo $a; echo $a | tr a-z A-z' | list_join ,
diff --git a/release.sh b/release.sh
deleted file mode 100755
index 219af38..0000000
--- a/release.sh
+++ /dev/null
@@ -1,47 +0,0 @@
-#!/bin/bash
-
-version=$(cat .version)
-
-release_version=${version%%-SNAPSHOT}
-new_version=$(echo $release_version+0.1 | bc)
-
-[[ $? -ne 0 ]] && echo 'Error exiting.' && exit 1
-
-snapshot_version=${new_version}-SNAPSHOT
-
-cat <<EOF
-
-    current version     : $version
-    release version     : $release_version
-    new snapshot version: $snapshot_version
-
-EOF
-
-git fetch
-
-echo start the release by creating a new release branch
-
-git checkout -b release/$release_version origin/develop
-echo $release_version > ./.version
-git add ./.version
-git commit -m "[release] prepare release v$release_version"
-git tag v$release_version
-echo $snapshot_version > ./.version
-git add ./.version
-git commit -m "[release] prepare for next development iteration"
-
-echo merge the version back into develop
-git checkout develop
-git merge --no-ff -m "[release] merge release/$release_version into develop" release/$release_version
-
-git checkout master
-echo merge the version back into master but use the tagged version instead of the release/$releaseVersion HEAD
-git merge --no-ff -m "[release] merge previous version into master to avoid the increased version number" release/$release_version~1
-
-echo get back on the develop branch
-git checkout develop
-echo finally push everything
-git push origin develop master
-git push --tags
-echo removing the release branch
-git branch -D release/$release_version
diff --git a/src/fun.sh b/src/fun.sh
old mode 100755
new mode 100644
index d0b3af8..533dd10
--- a/src/fun.sh
+++ b/src/fun.sh
@@ -1,318 +1,553 @@
-#!/bin/bash
-
-drop() {
-  command tail -n +$(($1 + 1))
-}
-
-take() {
-  command head -n ${1}
-}
-
-tail() {
-  drop 1
-}
-
-head() {
-  take 1
-}
-
-last() {
-  command tail -n 1
-}
+#!/bin/sh
 
+###############################################
+## List Functions
+###############################################
 list() {
-  for i in "$@"; do
-    echo "$i"
-  done
+    for i in "$@"; do
+        echo "$i"
+    done
 }
 
 unlist() {
-  cat - | xargs
+    xargs
 }
 
-append() {
-  cat -
-  list "$@"
+# Drop the first n items of a list.
+list_drop() {
+    command tail -n +$(($1 + 1))
 }
 
-prepend() {
-  list "$@"
-  cat -
+# Take the first n items of a list.
+list_take() {
+    command head -n "$1"
 }
 
+# Take the 'tail' of a list.
+# Otherwise known as dropping the first element.
+list_tail() {
+    list_drop 1
+}
 
+# Take only the first element of the list.
+list_head() {
+    list_take 1
+}
+
+# Take the last element of the list.
+list_last() {
+    command tail -n 1
+}
+
+# Add the contents of standard input
+# to the end of the list.
+list_append() {
+    cat -
+    list "$@"
+}
+
+# Add the contents of standard input
+# to the beginning of the list.
+list_prepend() {
+    list "$@"
+    cat -
+}
+
+###############################################
+## Lambdas and Lists
+###############################################
+# Defines an anonymous function.
 lambda() {
+    # shellcheck disable=2039
+    local expression
+    lam() {
+        # shellcheck disable=2039
+        local arg
+        while [ $# -gt 0 ]; do
+            arg="$1"
+            shift
+            if [ "$arg" = '.' ]; then
+                echo "$@"
+                return
+            else
+                echo "read $arg;"
+            fi
+        done
+    }
 
-  lam() {
-    local arg
-    while [[ $# -gt 0 ]]; do
-      arg="$1"
-      shift
-      if [[ $arg = '.' ]]; then
-        echo "$@"
-        return
-      else
-        echo "read $arg;"
-      fi
-    done
-  }
-
-  eval $(lam "$@")
-
+    expression=$(lam "$@")
+    eval "$expression"
 }
 
+# Same as lambda.
+# shellcheck disable=2039
 λ() {
-  lambda "$@"
+    lambda "$@"
 }
 
-map() {
-  local x
-  while read x; do
-    echo "$x" | "$@"
-  done
+# Print the number of arguments a lambda takes.
+# shellcheck disable=2039
+λ_num_args() {
+    # Calculates the number of arguments a lambda takes
+    minus "$#" 3
 }
 
-foldl() {
-  local f="$@"
-  local acc
-  read acc
-  while read elem; do
-    acc="$({ echo $acc; echo $elem; } | $f )"
-  done
-  echo "$acc"
-}
-
-foldr() {
-  local f="$@"
-  local acc
-  local zero
-  read zero
-  foldrr() {
-    local elem
-
-    if read elem; then
-        acc=$(foldrr)
-#        [[ -z $acc ]] && echo $elem && return
-    else
-        echo $zero && return
+# Perform an operation to each
+# element(s) of a list provided
+# through standard input.
+list_map() {
+    # shellcheck disable=2039
+    local x
+    # shellcheck disable=2039
+    local i
+    # shellcheck disable=2039
+    local arguments
+    # shellcheck disable=2039
+    local num_args
+    if [ "$1" = "λ" ] || [ "$1" = "lambda" ]; then
+        num_args=$(λ_num_args "$@")
+        while read -r x; do
+            arguments="$x"
+            i=2
+            while [ $i -le "$num_args" ] ; do
+                read -r x
+                arguments="$arguments $x"
+                i=$(add $i 1)
+            done
+            # We want to word split arguments, so no quotes
+            eval "list $arguments" | "$@"
+        done
+    else # Do not know the arity, assume 1
+        while read -r x; do
+            echo "$x" | "$@"
+        done
     fi
-
-    acc="$({ echo $acc; echo $elem; } | $f )"
-    echo "$acc"
-  }
-
-  foldrr
 }
 
+# Perform a binary operation on a list
+# where one element is the accumulation
+# of the results so far.
+# Ex: seq 3 | foldl lambda a b . 'minus $a $b'
+# First is (1 - 2 = -1) then (-1 - 3 = -4).
+foldl() {
+    # shellcheck disable=2039
+    local acc
+    read -r acc
+    while read -r elem; do
+        acc=$({ echo "$acc"; echo "$elem"; } | "$@" )
+    done
+    echo "$acc"
+}
+
+# Constructs a list where each element
+# is the foldl of the 0th-ith elements of
+# the list.
 scanl() {
-  local f="$@"
-  local acc
-  read acc
-  echo $acc
-  while read elem; do
-    acc="$({ echo $acc; echo $elem; } | $f )"
+    # shellcheck disable=2039
+    local acc
+    read -r acc
     echo "$acc"
-  done
+    while read -r elem; do
+        acc=$({ echo "$acc"; echo "$elem"; } | "$@" )
+        echo "$acc"
+    done
 }
 
-mul() {
-  ( set -f; echo $(($1 * $2)) )
+# Drops any elements of the list where the
+# function performed on it evaluates to false.
+filter() {
+    # shellcheck disable=2039
+    local x
+    while read -r x; do
+        ret=$(echo "$x" | "$@")
+        if_then "$ret" "echo $x"
+    done
 }
 
-plus() {
-  echo $(($1 + $2))
+# Keep taking elements until a certain condition
+# is false.
+take_while() {
+    # shellcheck disable=2039
+    local x
+    # shellcheck disable=2039
+    local condition
+    while read -r x; do
+        condition="$(echo "$x" | "$@")"
+        if_then_else "$condition" "echo $x" "break"
+    done
 }
 
-sub() {
-  echo $(($1 - $2))
+# Keep dropping elements until a certain condition
+# is false.
+drop_while() {
+    # shellcheck disable=2039
+    local x
+    while read -r x; do
+        condition="$(echo "$x" | "$@")"
+        if_then_else "$condition" 'do_nothing' 'break'
+    done
+    if_then "[ -n $x ]" "{ echo $x; cat -; }"
 }
 
-div() {
-  echo $(($1 / $2))
+
+###############################################
+## Arithmetic Functions
+###############################################
+multiply() {
+    # shellcheck disable=2039
+    local a
+    # shellcheck disable=2039
+    local b
+    a=$1
+    if [ $# -lt 2 ] ; then
+        read -r b
+    else
+        b=$2
+    fi
+    isint "$a" > /dev/null && \
+    isint "$b" > /dev/null && \
+    echo $((a * b))
+}
+
+add() {
+    # shellcheck disable=2039
+    local a
+    # shellcheck disable=2039
+    local b
+    a=$1
+    if [ $# -lt 2 ] ; then
+        read -r b
+    else
+        b=$2
+    fi
+    isint "$a" > /dev/null && \
+    isint "$b" > /dev/null && \
+    echo $((a + b))
+}
+
+minus() {
+    # shellcheck disable=2039
+    local a
+    # shellcheck disable=2039
+    local b
+    a=$1
+    if [ $# -lt 2 ] ; then
+        b=$1
+	read -r a
+    else
+        b=$2
+    fi
+    isint "$a" > /dev/null && \
+    isint "$b" > /dev/null && \
+    echo $((a - b))
+}
+
+divide() {
+    # shellcheck disable=2039
+    local a
+    # shellcheck disable=2039
+    local b
+    a=$1
+    if [ $# -lt 2 ] ; then
+        b=$1
+	read -r a
+    else
+        b=$2
+    fi
+    isint "$a" > /dev/null && \
+    isint "$b" > /dev/null && \
+    echo $((a / b))
 }
 
 mod() {
-  echo $(($1 % $2))
+    # shellcheck disable=2039
+    local a
+    # shellcheck disable=2039
+    local b
+    a=$1
+    if [ $# -lt 2 ] ; then
+        b=$1
+	read -r a
+    else
+        b=$2
+    fi
+    isint "$a" > /dev/null && \
+    isint "$b" > /dev/null && \
+    echo $((a % b))
 }
 
+even() {
+    # shellcheck disable=2039
+    local n
+    # shellcheck disable=2039
+    local result
+    # shellcheck disable=2039
+    local result_code
+    if [ $# -lt 1 ] ; then
+        read -r n
+    else
+        n=$1
+    fi
+    result=$(mod "$n" 2)
+    result_code=$?
+    if [ $result_code -ne 0 ] ; then
+        ret false
+    else
+        result_to_bool "[ $result = 0 ]"
+    fi
+}
+
+odd() {
+    not even
+}
+
+less_than() {
+    # shellcheck disable=2039
+    local n
+    read -r n
+    if isint "$n" > /dev/null && \
+       [ "$n" -lt "$1" ] ; then
+        ret true
+    else
+        ret false
+    fi
+}
 
 sum() {
-  foldl lambda a b . 'echo $(($a + $b))'
+    foldl lambda a b . "add \$a \$b"
 }
 
 product() {
-  foldl lambda a b . 'echo $(mul $a $b)'
+    foldl lambda a b . "multiply \$a \$b"
 }
 
 factorial() {
-  seq 1 $1 | product
+    seq 1 "$1" | product
 }
 
+###############################################
+## String Operations
+###############################################
+# Splits a string into a list where each element
+# is one character.
 splitc() {
-  cat - | sed 's/./&\n/g'
+    sed 's/./\n&/g' | list_tail
 }
 
-join() {
-  local delim=$1
-  local pref=$2
-  local suff=$3
-  echo $pref$(cat - | foldl lambda a b . 'echo $a$delim$b')$suff
+# Takes a list and creates a string where
+# each element is seperated by a delimiter.
+list_join() {
+    # shellcheck disable=2039
+    local delim
+    delim=$1
+    foldl lambda a b . "echo \$a$delim\$b"
 }
 
+# Split a string into a list
+# by a specified delimeter
+str_split() {
+    sed "s/$1/\n/g"
+}
+
+# Reverses a list.
 revers() {
-  foldl lambda a b . 'append $b $a'
+    # shellcheck disable=2039
+    local result
+    # shellcheck disable=2039
+    local n
+    while read -r n; do
+        result="$n\n$result"
+    done
+    echo "$result"
 }
 
+# Reverses a string
 revers_str() {
-  cat - | splitc | revers | join
+    splitc | revers | list_join
 }
 
-catch() {
-  local f="$@"
-  local cmd=$(cat -)
-  local val=$(2>&1 eval "$cmd"; echo $?)
-  local cnt=$(list $val | wc -l)
-  local status=$(list $val | last)
-  $f < <(list "$cmd" $status $(list $val | take $((cnt - 1)) | unlist | tup))
+# Removes multiple occurences of
+# a single character from the beginning
+# of the list.
+lstrip() {
+    # shellcheck disable=2039
+    local c
+    if [ $# -eq 0 ] ; then
+        c=" "
+    else
+        c="$1"
+    fi
+    sed "s/^$c*//g"
 }
 
-try() {
-  local f="$@"
-  catch lambda cmd status val . '[[ $status -eq 0 ]] && tupx 1- $val | unlist || { '"$f"' < <(list $status); }'
+# Removes multiple occurences of
+# a single character from the end
+# of the list.
+rstrip() {
+    # shellcheck disable=2039
+    local c
+    if [ $# -eq 0 ] ; then
+        c=" "
+    else
+        c="$1"
+    fi
+    sed "s/$c*$//g"
+}
+
+# Removes multiple occurences of
+# a single character from the beginning
+# and end of the list.
+strip() {
+    lstrip "$@" | rstrip "$@"
+}
+
+###############################################
+## Tuple Functions
+###############################################
+
+# Creates a tuple, which is a string with
+# multiple elements seperated by a comma,
+# and it begins with a ( and ends with a ).
+tup() {
+    # shellcheck disable=2039
+    local args
+    # shellcheck disable=2039
+    local result
+    if [ $# -eq 0 ]; then
+        args=$(unlist)
+        eval "tup $args"
+    else
+        result=$(list "$@" | list_join ,)
+        echo "($result)"
+    fi
+}
+
+# Takes a tuple and outputs it as a list
+tup_to_list() {
+    local li
+    local f
+    local la
+    li=$(str_split ",")
+
+    # Remove '(' from the first element
+    f=$(echo "$li" | list_head)
+    f=$(echo "$f" | sed 's/^(//')
+
+    la=$(echo "$li" | list_last)
+    # If there is only one element in the list
+    # Remove ')' from the only element
+    if [ "$(echo "$la" | cut -c1)" = "(" ]; then
+        f=$(echo "$f" | sed "s/)$//")
+        echo "$f"
+    # If there is more than one element in the list
+    # Remove ')' from the last element
+    else
+        la=$(echo "$la" | sed "s/)$//")
+        # Remove the first and last element from li
+        li=$(echo "$li" | list_tail | sed '$d')
+        # Print the list
+        { echo "$f"; echo "$li"; echo "$la"; }
+    fi
+}
+
+# Takes the first element of the tuple
+tupl() {
+    tup_to_list | list_head
+}
+
+# Takes the last element of the tuple
+tupr() {
+    tup_to_list | list_last
+}
+
+
+# Takes each element from a list in standard
+# input and matches it with a list provided
+# as the argument to this function.
+# The result is a list of 2-tuples.
+list_zip() {
+    # shellcheck disable=2039
+    local l
+    l=$(list "$@")
+    while read -r x; do
+        y=$(echo "$l" | list_take 1)
+        tup "$x" "$y"
+        l=$(echo "$l" | list_drop 1)
+    done
+}
+
+###############################################
+## Logic Based Functions
+###############################################
+
+if_then() {
+    # shellcheck disable=2039
+    local result
+    eval "$1"
+    result=$?
+    if [ $result -eq 0 ] ; then
+        eval "$2"
+    fi
+}
+
+if_then_else() {
+    # shellcheck disable=2039
+    local result
+    eval "$1"
+    result=$?
+    if [ $result -eq 0 ] ; then
+        eval "$2"
+    else
+        eval "$3"
+    fi
+}
+
+result_to_bool() {
+    if_then_else "$1" 'ret true' 'ret false'
+}
+
+not() {
+    if_then_else "$1 > /dev/null" "ret false" "ret true"
 }
 
 ret() {
-  echo $@
+    echo "$@"
+    "$@"
 }
 
-filter() {
-  local x
-  while read x; do
-    ret=$(echo "$x" | "$@")
-    $ret && echo $x
-  done
+do_nothing() {
+    echo > /dev/null
 }
 
-pass() {
-  echo > /dev/null
+
+###############################################
+## Useful utility functions
+###############################################
+
+isint() {
+    result_to_bool "echo \"$1\" | grep -Eq '^-?[0-9]+$'"
 }
 
-dropw() {
-  local x
-  while read x && $(echo "$x" | "$@"); do
-    pass
-  done
-  [[ ! -z $x ]] && { echo $x; cat -; }
+isempty() {
+    result_to_bool "[ -z \"$1\" ]"
 }
 
-peek() {
-  local x
-  while read x; do
-    ([ $# -eq 0 ] && 1>&2 echo $x || 1>&2 "$@" < <(echo $x))
-    echo $x
-  done
+isfile() {
+    result_to_bool "[ -f \"$1\" ]"
 }
 
-stripl() {
-  local arg=$1
-  cat - | map lambda l . 'ret ${l##'$arg'}'
+isnonzerofile() {
+    result_to_bool "[ -s \"$1\" ]"
 }
 
-stripr() {
-  local arg=$1
-  cat - | map lambda l . 'ret ${l%%'$arg'}'
+isreadable() {
+    result_to_bool "[ -r \"$1\" ]"
 }
 
-strip() {
-  local arg=$1
-  cat - | stripl "$arg" | stripr "$arg"
+iswritable() {
+    result_to_bool "[ -w \"$1\" ]"
 }
 
-buff() {
-  local cnt=-1
-  for x in $@; do
-    [[ $x = '.' ]] && break
-    cnt=$(plus $cnt 1)
-  done
-  local args=''
-  local i=$cnt
-  while read arg; do
-    [[ $i -eq 0 ]] && list $args | "$@" && i=$cnt && args=''
-    args="$args $arg"
-    i=$(sub $i 1)
-  done
-  [[ ! -z $args ]] && list $args | "$@"
-}
-
-tup() {
-  if [[ $# -eq 0 ]]; then
-    local arg
-    read arg
-    tup $arg
-  else
-    list "$@" | map lambda x . 'echo ${x/,/u002c}' | join , '(' ')'
-  fi
-}
-
-tupx() {
-  if [[ $# -eq 1 ]]; then
-    local arg
-    read arg
-    tupx "$1" "$arg"
-  else
-    local n=$1
-    shift
-    echo "$@" | stripl '(' | stripr ')' | cut -d',' -f${n} | tr ',' '\n' | map lambda x . 'echo ${x/u002c/,}'
-  fi
-}
-
-tupl() {
-  tupx 1 "$@"
-}
-
-tupr() {
-  tupx 1- "$@" | last
-}
-
-zip() {
-  local list=$*
-  cat - | while read x; do
-    y=$(list $list | take 1)
-    tup $x $y
-    list=$(list $list | drop 1)
-  done
-}
-
-curry() {
-  exportfun=$1; shift
-  fun=$1; shift
-  params=$*
-  cmd=$"function $exportfun() {
-      more_params=\$*;
-      $fun $params \$more_params;
-  }"
-  eval $cmd
-}
-
-with_trampoline() {
-  local f=$1; shift
-  local args=$@
-  while [[ $f != 'None' ]]; do
-    ret=$($f $args)
-#    echo $ret
-    f=$(tupl $ret)
-    args=$(echo $ret | tupx 2- | tr ',' ' ')
-  done
-  echo $args
-}
-
-res() {
-    local value=$1
-    tup "None" $value
-}
-
-call() {
-    local f=$1; shift
-    local args=$@
-    tup $f $args
+isdir() {
+    result_to_bool "[ -d \"$1\" ]"
 }
diff --git a/test/append_test.sh b/test/append_test.sh
index e6ceb99..2ee28fc 100755
--- a/test/append_test.sh
+++ b/test/append_test.sh
@@ -1,15 +1,15 @@
 #! /bin/bash
 
 testAppendToEmptyList() {
-  assertEquals 4 "$(list | append 4)"
+  assertEquals 4 "$(list | list_append 4)"
 }
 
 testAppendToOneElementList() {
-  assertEquals "1 4" "$(list 1 | append 4 | unlist)"
+  assertEquals "1 4" "$(list 1 | list_append 4 | unlist)"
 }
 
 testAppendToList() {
-  assertEquals "1 2 3 4 5 4" "$(list 1 2 3 4 5 | append 4 | unlist)"
+  assertEquals "1 2 3 4 5 4" "$(list 1 2 3 4 5 | list_append 4 | unlist)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/catch_test.sh b/test/catch_test.sh
deleted file mode 100755
index b3f0917..0000000
--- a/test/catch_test.sh
+++ /dev/null
@@ -1,19 +0,0 @@
-#! /bin/bash
-
-testCatchIfSuccess() {
-  assertEquals 1 "$(echo 'expr 2 / 2' | catch lambda cmd status val . '[[ $status -eq 0 ]] && tupl $val || echo 0')"
-}
-
-testCatchIfError() {
-  assertEquals 0 $(echo 'expr 2 / 0' | catch lambda cmd status val . '[[ $status -eq 0 ]] && tupl $val || echo 0')
-  assertEquals 'cmd=expr 2 / 0,status=2,val=(expr:,division,by,zero)' "$(echo 'expr 2 / 0' | echo 'expr 2 / 0' | LANG=en catch lambda cmd status val . 'echo cmd=$cmd,status=$status,val=$val')"
-}
-
-testCatchEdgeCases() {
-  assertEquals 1 "$(echo 'expr 2 / 2' | catch lambda _ _ val . 'tupl $val')"
-  assertEquals 'expr 2 / 2' "$(echo 'expr 2 / 2' | catch lambda cmd . 'ret $cmd')"
-  assertEquals 'expr 2 / 2,0' "$(echo 'expr 2 / 2' | catch lambda cmd status . 'ret $cmd,$status')"
-  assertEquals 'expr 2 / 0,2' "$(echo 'expr 2 / 0' | catch lambda cmd status . 'ret $cmd,$status')"
-}
-
-. ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/drop_test.sh b/test/drop_test.sh
index 5aef523..7195d48 100755
--- a/test/drop_test.sh
+++ b/test/drop_test.sh
@@ -1,23 +1,23 @@
 #! /bin/bash
 
 testDrop9From10() {
-  assertEquals 10 $(list {1..10} | drop 9)
+  assertEquals 10 $(list {1..10} | list_drop 9)
 }
 
 testDrop8From10() {
-  assertEquals "9 10" "$(list {1..10} | drop 8 | unlist)"
+  assertEquals "9 10" "$(list {1..10} | list_drop 8 | unlist)"
 }
 
 testDropAll() {
-  assertEquals "" "$(list {1..10} | drop 10)"
+  assertEquals "" "$(list {1..10} | list_drop 10)"
 }
 
 testDropMoreThanAvailable() {
-  assertEquals "" "$(list {1..10} | drop 15)"
+  assertEquals "" "$(list {1..10} | list_drop 15)"
 }
 
 testDropZero() {
-  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | drop 0 | unlist)"
+  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | list_drop 0 | unlist)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/head_test.sh b/test/head_test.sh
index 3ea2a7f..0293890 100755
--- a/test/head_test.sh
+++ b/test/head_test.sh
@@ -1,16 +1,16 @@
 #! /bin/bash
 
-testHeadFromList() {
-  assertEquals 1 $(list {1..10} | head)
-  assertEquals 5 $(list 5 6 7 | head)
+testLHeadFromList() {
+  assertEquals 1 $(list {1..10} | list_head)
+  assertEquals 5 $(list 5 6 7 | list_head)
 }
 
-testHeadFromOneElementList() {
-  assertEquals 1 $(list 1 | head)
+testLHeadFromOneElementList() {
+  assertEquals 1 $(list 1 | list_head)
 }
 
-testHeadFromEmptyList() {
-  assertEquals "" "$(list | head)"
+testLHeadFromEmptyList() {
+  assertEquals "" "$(list | list_head)"
 }
 
-. ./shunit2-init.sh
\ No newline at end of file
+. ./shunit2-init.sh
diff --git a/test/last_test.sh b/test/last_test.sh
index e76a694..e10ec36 100755
--- a/test/last_test.sh
+++ b/test/last_test.sh
@@ -1,16 +1,16 @@
 #! /bin/bash
 
 testLastFromList() {
-  assertEquals 10 $(list {1..10} | last)
-  assertEquals 7 $(list 5 6 7 | last)
+  assertEquals 10 $(list {1..10} | list_last)
+  assertEquals 7 $(list 5 6 7 | list_last)
 }
 
 testLastFromOneElementList() {
-  assertEquals 1 $(list 1 | last)
+  assertEquals 1 $(list 1 | list_last)
 }
 
 testLastFromEmptyList() {
-  assertEquals "" "$(list | last)"
+  assertEquals "" "$(list | list_last)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/map_test.sh b/test/map_test.sh
index b34217c..383a8a8 100755
--- a/test/map_test.sh
+++ b/test/map_test.sh
@@ -1,33 +1,33 @@
 #!/bin/bash
 
 testMapEmptyList() {
-  assertEquals "" "$(list | map lambda x . 'echo $(($x + 1))')"
+  assertEquals "" "$(list | list_map lambda x . 'echo $(($x + 1))')"
 }
 
 testMapEmptyList_ifNoArgumentsInLambda() {
-  assertEquals "" "$(list | map lambda . 'echo 3')"
+  assertEquals "" "$(list | list_map lambda . 'echo 3')"
 }
 
 testMapOneElementList() {
-  assertEquals "3" "$(list 2 | map lambda x . 'echo $(($x + 1))')"
+  assertEquals "3" "$(list 2 | list_map lambda x . 'echo $(($x + 1))')"
 }
 
 testMapList() {
-  assertEquals "2 3 4 5 6" "$(list {1..5} | map lambda x . 'echo $(($x + 1))' | unlist)"
+  assertEquals "2 3 4 5 6" "$(list {1..5} | list_map lambda x . 'echo $(($x + 1))' | unlist)"
 }
 
 testMapList_ifNoArgumentsInLambda() {
-  assertEquals "9 9 9 9 9" "$(list {1..5} | map lambda . 'echo 9' | unlist)"
+  assertEquals "9 9 9 9 9" "$(list {1..5} | list_map lambda . 'echo 9' | unlist)"
 }
 
 testMapList_ifManyArgumentsInLambda() {
-  list {1..5} | map lambda x y . 'echo $(($x + $y))' 2> /dev/null \
+  list {1..5} | list_map lambda x y . 'echo $(($x + $y))' 2> /dev/null \
     && fail "There should be syntax error, because map is an one argument operation"
 }
 
 testFlatMap() {
-    assertEquals "1 2 3 2 3 3" "$(list {1..3} | map lambda x . 'seq $x 3' | unlist)"
-    assertEquals "d e h l l l o o r w" "$(list hello world | map lambda x . 'command fold -w 1 <<< $x' | sort | unlist)"
+    assertEquals "1 2 3 2 3 3" "$(list {1..3} | list_map lambda x . 'seq $x 3' | unlist)"
+    assertEquals "d e h l l l o o r w" "$(list hello world | list_map lambda x . 'command fold -w 1 <<< $x' | sort | unlist)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/predicates_test.sh b/test/predicates_test.sh
new file mode 100755
index 0000000..5e96337
--- /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
diff --git a/test/prepend_test.sh b/test/prepend_test.sh
index 8e9e3a0..491a56e 100755
--- a/test/prepend_test.sh
+++ b/test/prepend_test.sh
@@ -1,15 +1,15 @@
 #! /bin/bash
 
 testPrependToEmptyList() {
-  assertEquals 4 "$(list | prepend 4)"
+  assertEquals 4 "$(list | list_prepend 4)"
 }
 
 testPrependToOneElementList() {
-  assertEquals "4 1" "$(list 1 | prepend 4 | unlist)"
+  assertEquals "4 1" "$(list 1 | list_prepend 4 | unlist)"
 }
 
 testPrependToList() {
-  assertEquals "4 1 2 3 4 5" "$(list 1 2 3 4 5 | prepend 4 | unlist)"
+  assertEquals "4 1 2 3 4 5" "$(list 1 2 3 4 5 | list_prepend 4 | unlist)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/tail_test.sh b/test/tail_test.sh
index 57971ad..f6c11e6 100755
--- a/test/tail_test.sh
+++ b/test/tail_test.sh
@@ -1,15 +1,15 @@
 #! /bin/bash
 
-testTailFrom10() {
-  assertEquals "2 3 4 5 6 7 8 9 10" "$(list {1..10} | tail | unlist)"
+testLTailFrom10() {
+  assertEquals "2 3 4 5 6 7 8 9 10" "$(list {1..10} | list_tail | unlist)"
 }
 
-testTailFromOneElementList() {
-  assertEquals "" "$(list 1 | tail)"
+testLTailFromOneElementList() {
+  assertEquals "" "$(list 1 | list_tail)"
 }
 
-testTailFromEmptyList() {
-  assertEquals "" "$(list | tail)"
+testLTailFromEmptyList() {
+  assertEquals "" "$(list | list_tail)"
 }
 
-. ./shunit2-init.sh
\ No newline at end of file
+. ./shunit2-init.sh
diff --git a/test/take_test.sh b/test/take_test.sh
index efd48ef..5b0cb49 100755
--- a/test/take_test.sh
+++ b/test/take_test.sh
@@ -1,23 +1,23 @@
 #! /bin/bash
 
 testTake9From10() {
-  assertEquals "1 2 3 4 5 6 7 8 9" "$(list {1..10} | take 9 | unlist)"
+  assertEquals "1 2 3 4 5 6 7 8 9" "$(list {1..10} | list_take 9 | unlist)"
 }
 
 testTake8From10() {
-  assertEquals "1 2 3 4 5 6 7 8" "$(list {1..10} | take 8 | unlist)"
+  assertEquals "1 2 3 4 5 6 7 8" "$(list {1..10} | list_take 8 | unlist)"
 }
 
 testTakeAll() {
-  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | take 10 | unlist)"
+  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | list_take 10 | unlist)"
 }
 
 testTakeMoreThanAvailable() {
-  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | take 15 | unlist)"
+  assertEquals "1 2 3 4 5 6 7 8 9 10" "$(list {1..10} | list_take 15 | unlist)"
 }
 
 testTakeZero() {
-  assertEquals "" "$(list {1..10} | take 0 | unlist)"
+  assertEquals "" "$(list {1..10} | list_take 0 | unlist)"
 }
 
 . ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/try_test.sh b/test/try_test.sh
deleted file mode 100755
index be1aeb3..0000000
--- a/test/try_test.sh
+++ /dev/null
@@ -1,11 +0,0 @@
-#! /bin/bash
-
-testTry() {
-  assertEquals 1 "$(echo 'expr 2 / 2' | try lambda _ . 'ret 0')"
-  assertEquals 0 "$(echo 'expr 2 / 0' | try lambda _ . 'ret 0')"
-  assertEquals 2 "$(echo 'expr 2 / 0' | try lambda status . 'ret $status')"
-  assertEquals 'already up to date' "$(echo 'echo already up to date' | try lambda _ . 'ret error')"
-  assertEquals 'error exit 1' "$(try λ  _ . 'echo "error"; echo exit 1' < <(echo fgit pull) | unlist)"
-}
-
-. ./shunit2-init.sh
\ No newline at end of file
diff --git a/test/tup_test.sh b/test/tup_test.sh
index bdd5ac1..71f1b05 100755
--- a/test/tup_test.sh
+++ b/test/tup_test.sh
@@ -8,7 +8,8 @@ testTupIfOneElement() {
   assertEquals '(1)' $(tup 1)
   assertEquals '(")' $(tup '"')
   assertEquals "(')" $(tup "'")
-  assertEquals "(u002c)" $(tup ",")
+  assertEquals "(,)" $(tup ",")
+  assertEquals "(,,)" $(tup ",,")
   assertEquals "(()" $(tup "(")
   assertEquals "())" $(tup ")")
 }
@@ -19,40 +20,10 @@ testTupHappyPath() {
   assertEquals '(a b,c d e,f)' "$(tup 'a b' 'c d e' 'f')"
 }
 
-testTupxHappyPath() {
-  assertEquals '4' $(tup 4 5 1 4 | tupx 1)
-  assertEquals '5' $(tup 4 5 1 4 | tupx 2)
-  assertEquals '1' $(tup 4 5 1 4 | tupx 3)
-  assertEquals '4' $(tup 4 5 1 4 | tupx 4)
-
-}
-
-testTupxIfEmpty() {
-  assertEquals '' "$(tup '' | tupx 1)"
-  assertEquals '' "$(tup '' | tupx 5)"
-}
-
 testTupxIfZeroIndex() {
   assertEquals '' "$(tup 1 3 | tupx 0 2>/dev/null)"
 }
 
-testTupxIfSpecialChars() {
-  assertEquals ',' "$(tup ',' | tupx 1)"
-  assertEquals '(' "$(tup '(' | tupx 1)"
-  assertEquals ')' "$(tup ')' | tupx 1)"
-  assertEquals '()' "$(tup '()' | tupx 1)"
-  assertEquals '(' "$(tup '(' ')' | tupx 1)"
-  assertEquals '(' "$(tup '(' '(' | tupx 1)"
-  assertEquals ')' "$(tup ')' ')' | tupx 1)"
-  assertEquals ',' "$(tup 'u002c' | tupx 1)"
-}
-
-testTupxRange() {
-  assertEquals '4 5' "$(tup 4 5 1 4 | tupx 1-2 | unlist)"
-  assertEquals '4 4' "$(tup 4 5 1 4 | tupx 1,4 | unlist)"
-  assertEquals '4 5 4' "$(tup 4 5 1 4 | tupx 1,2,4 | unlist)"
-}
-
 testTupl() {
   assertEquals '4' "$(tup 4 5 | tupl)"
   assertEquals '4' "$(tup 4 5 6 | tupl)"
@@ -66,4 +37,4 @@ testTupr() {
   assertEquals '5' "$(tup 5 | tupr)"
 }
 
-. ./shunit2-init.sh
\ No newline at end of file
+. ./shunit2-init.sh