maybe monad and friends
maybe - return a tuple of (Nothing) or (Just,value) maybemap - apply map function when maybe has a value and wrap in another maybe; else when nothing return nothing maybevalue - return value of maybe; else when nothing return optional default args
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40
src/fun.sh
40
src/fun.sh
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@ -358,3 +358,43 @@ call() {
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local args=$@
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tup $f $args
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}
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maybe() {
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if [[ $# -eq 0 ]]; then
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local arg
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read arg
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maybe "$arg"
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else
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local x="$*"
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local value=$(echo $x | strip)
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if [[ ${#value} -eq 0 ]]; then
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tup Nothing
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else
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tup Just "$value"
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fi
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fi
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}
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maybemap() {
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local x
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read x
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if [[ $(tupl $x) = "Nothing" ]]; then
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echo $x
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else
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local y=$(tupr "$x")
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local r=$(echo "$y" | map "$@")
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maybe "$r"
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fi
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}
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maybevalue() {
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local default="$*"
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local x
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read x
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if [[ $(tupl $x) = "Nothing" ]]; then
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echo "$default"
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else
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echo $(tupr $x)
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fi
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}
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29
test/maybe_test.sh
Executable file
29
test/maybe_test.sh
Executable file
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@ -0,0 +1,29 @@
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#! /bin/bash
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testMaybe() {
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assertEquals '(Just,1)' "$(maybe 1)"
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assertEquals '(Just,1)' "$(echo 1 | maybe)"
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assertEquals '(Nothing)' "$(maybe '')"
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assertEquals '(Nothing)' "$(maybe ' ')"
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assertEquals '(Nothing)' "$(maybe ' ' ' ' ' ')"
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assertEquals '(Nothing)' "$(echo | maybe)"
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assertEquals '(Just,1 2 3)' "$(maybe 1 2 3)"
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assertEquals '(Just,1 2 3)' "$(echo 1 2 3 | maybe)"
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}
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testMaybemap() {
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assertEquals '(Just,3)' "$(echo 1 | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo $(( a + 1 ))')"
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assertEquals '(Nothing)' "$(echo | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo $(( a + 1 ))')"
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assertEquals '(Nothing)' "$(echo 1 | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo')"
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assertEquals '(Nothing)' "$(echo 1 | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo' | maybemap lambda a . 'echo $(( a + 1 ))')"
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}
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testMaybevalue() {
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assertEquals 3 "$(echo 1 | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo $(( a + 1 ))' | maybevalue 0)"
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assertEquals 0 "$(echo | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo $(( a + 1 ))' | maybevalue 0)"
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assertEquals 'a b c' "$(echo | maybe | maybemap lambda a . 'echo $(( a + 1 ))' | maybemap lambda a . 'echo $(( a + 1 ))' | maybevalue a b c)"
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}
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. ./shunit2-init.sh
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