ssledz / bash-fun

Functional programming in bash

Introduction

Introduction to fun.sh library

Quick start

#!/bin/bash
. <(test -e fun.sh || curl -Ls https://raw.githubusercontent.com/ssledz/bash-fun/master/src/fun.sh > fun.sh; cat fun.sh)

seq 1 4 | sum

Functions overview

append	buff	call	catch	curry	div
drop	dropw	factorial	filter	foldl	foldr
isint	isempty	isfile	isnonzerofile	isreadable	iswritable
isdir	join	lambda	last	lhead	list
ltail	lzip	map	maybe	maybemap	maybevalue
mod	mul	not	ntup	ntupl	ntupr
ntupx	peek	plus	prepend	product	ret
res	revers	revers_str	scanl	splitc	strip
stripl	stripr	sub	sum	take	try
tup	tupl	tupr	tupx	unlist	λ
with_trampoline

list/unlist

$ list 1 2 3
1
2
3

$ list 1 2 3 4 5 | unlist
1 2 3 4 5

take/drop/ltail/lhead/last

$ list 1 2 3 4 | drop 2
3
4

$ list 1 2 3 4 5 | lhead
1

$ list 1 2 3 4 | ltail
2
3
4

$ list 1 2 3 4 5 | last
5

$ list 1 2 3 4 5 | take 2
1
2

join

$ list 1 2 3 4 5 | join ,
1,2,3,4,5

$ list 1 2 3 4 5 | join , [ ]
[1,2,3,4,5]

map

$ seq 1 5 | 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)'
aA
bB
sS
dD
eE

$ list 1 2 3 | map echo
1
2
3

$ list 1 2 3 | map 'echo $ is a number'
1 is a number
2 is a number
3 is a number

$ list 1 2 3 4 | map 'echo \($,$\) is a point'
(1,1) is a point
(2,2) is a point
(3,3) is a point
(4,4) is a point

flat map

$ 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

$ seq 1 10 | filter λ a . '[[ $(mod $a 2) -eq 0 ]] && ret true || ret false'
2
4
6
8
10

foldl/foldr

$ 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

$ seq 1 4 | foldl λ acc el . 'echo $(($acc + $el))'
10

$ seq 1 4 | foldl λ acc el . 'echo $(mul $(($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

$ tup a 1
(a,1)

$ tup 'foo bar' 1 'one' 2
(foo bar,1,one,2)

$ tup , 1 3
(u002c,1,3)

$ tupl $(tup a 1)
a

$ tupr $(tup a 1)
1

$ tup , 1 3 | tupl
,

$ tup 'foo bar' 1 'one' 2 | tupl
foo bar

$ tup 'foo bar' 1 'one' 2 | tupr
2

$ 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

ntup/ntupx/ntupl/ntupr

$ ntup tuples that $(ntup safely nest)
(dHVwbGVzCg==,dGhhdAo=,KGMyRm1aV3g1Q2c9PSxibVZ6ZEFvPSkK)

echo '(dHVwbGVzCg==,dGhhdAo=,KGMyRm1aV3g1Q2c9PSxibVZ6ZEFvPSkK)' | ntupx 3 | ntupr
nest

$ ntup 'foo,bar' 1 one 1
(Zm9vLGJhcgo=,MQo=,b25lCg==,MQo=)

$ echo '(Zm9vLGJhcgo=,MQo=,b25lCg==,MQo=)' | ntupx 1
foo,bar

$ ntupl $(ntup 'foo bar' 1 one 2)
foo bar

$ ntupr $(ntup 'foo bar' 1 one 2)
2

buff

$ 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

lzip

$ list a b c d e f | lzip $(seq 1 10)
(a,1)
(b,2)
(c,3)
(d,4)
(e,5)
(f,6)

$ list a b c d e f | lzip $(seq 1 10) | last | tupr
6

curry

add2() {
    echo $(($1 + $2))
}

$ curry inc add2 1

$ inc 2
3

$ seq 1 3 | map λ a . 'inc $a'
2
3
4

peek

$ list 1 2 3 \
    | peek lambda a . echo 'dbg a : $a' \
    | map lambda a . 'mul $a 2' \
    | peek lambda a . echo 'dbg b : $a' \
    | sum

dbg a : 1
dbg a : 2
dbg a : 3
dbg b : 2
dbg b : 4
dbg b : 6
12

$ a=$(seq 1 4 | peek lambda a . echo 'dbg: $a' | sum)

dbg: 1
dbg: 2
dbg: 3
dbg: 4

$ echo $a

10

maybe/maybemap/maybevalue

$ list Hello | maybe
(Just,Hello)

$ list "   " | maybe
(Nothing)

$ list Hello | maybe | maybemap λ a . 'tr oH Oh <<<$a'
(Just,hellO)

$ list "   " | maybe | maybemap λ a . 'tr oH Oh <<<$a'
(Nothing)

$ echo bash-fun rocks | maybe | maybevalue DEFAULT
bash-fun rocks

$ echo | maybe | maybevalue DEFAULT
DEFAULT

not/isint/isempty

$ isint 42
true

$ list blah | isint
false

$ not true
false

$ not isint 777
false

$ list 1 2 "" c d 6 | filter λ a . 'isint $a'
1
2
6

$ list 1 2 "" c d 6 | filter λ a . 'not isempty $a'
1
2
c
d
6

isfile/isnonzerofile/isreadable/iswritable/isdir

$ 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

try/catch

$ 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'
1

try λ  _ . 'echo some errors during pull; exit 1' < <(echo git pull)

$ 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)

$ echo 'expr 2 / 2' | catch λ _ _ val . 'tupl $val'
1

scanl

$ seq 1 5 | scanl lambda acc el . 'echo $(($acc + $el))'
1
3
6
10
15

$ seq 1 5 | scanl lambda a b . 'echo $(($a + $b))' | last
15

with_trampoline/res/call

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
}

$ time factorial 30 | fold -w 70
265252859812191058636308480000000

real    0m1.854s
user    0m0.072s
sys     0m0.368s

time factorial 60 | fold -w 70
8320987112741390144276341183223364380754172606361245952449277696409600
000000000000

real    0m3.635s
user    0m0.148s
sys     0m0.692s

$ time factorial 90 | fold -w 70
1485715964481761497309522733620825737885569961284688766942216863704985
393094065876545992131370884059645617234469978112000000000000000000000

real    0m4.371s
user    0m0.108s
sys     0m0.436s

Examples

processNames() {

  uppercase() {
     local str=$1
     echo $(tr 'a-z' 'A-Z' <<< ${str:0:1})${str:1}
  }

  list $@ \
    | filter λ name . '[[ ${#name} -gt 1 ]] && ret true || ret false' \
    | map λ name . 'uppercase $name' \
    | foldl λ acc el . 'echo $acc,$el'

}

processNames adam monika s slawek d daniel Bartek j k

Adam,Monika,Slawek,Daniel,Bartek

Running tests

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
• Functional Programming in Bash