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

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/unlist

$ list 1 2 3
1
2
3

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

take/drop/tail/head/last

$ list 1 2 3 4 | drop 2
3
4

$ list 1 2 3 4 5 | head
1

$ list 1 2 3 4 | tail
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

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

zip

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

$ list a b c d e f | zip $(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

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

Resources

• Inspiration
• Functional Programming in Bash