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< title > Higher order function in zsh< / title >
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2011-10-18 22:30:00 +00:00
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Higher order function in zsh
< / h1 >
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< div class = "intro" >
< p > < span class = "sc" > < abbr title = "Too long; didn't read" > tl;dr< / abbr > : < / span > some simple implementation of higher order function for zsh.< / p >
< / div >
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< p > Why is it important to have these functions?
Simply because, the more I programmed with zsh the more I tended to work using functional programming style.< / p >
< p > The minimal to have better code are the functions < code > map< / code > , < code > filter< / code > and < code > fold< / code > .< / p >
< p > Let’ s compare.
First a program which convert all gif to png in many different directories of different projects.< / p >
< p > Before ⇒< / p >
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< pre class = "twilight" >
< span class = "Comment" > < span class = "Comment" > #< / span > for each directory in projects dir< / span >
< span class = "Keyword" > for< / span > toProject < span class = "Keyword" > in< / span > /path/to/projects/*(/N)< span class = "Keyword" > ;< / span > < span class = "Keyword" > do< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > toProject is /path/to/projects/foo< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > project become foo (:t for tail)< / span >
project=< span class = "Variable" > < span class = "Variable" > ${< / span > toProject:t< span class = "Variable" > }< / span > < / span >
< span class = "Keyword" > for< / span > toResource < span class = "Keyword" > in< / span > < span class = "Variable" > < span class = "Variable" > $< / span > toProject< / span > /resources/*.gif(.N)< span class = "Keyword" > ;< / span > < span class = "Keyword" > do< / span >
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convert < span class = "Variable" > < span class = "Variable" > $< / span > toResource< / span > < span class = "Variable" > < span class = "Variable" > ${< / span > toResource:r< span class = "Variable" > }< / span > < / span > .png < span class = "Keyword" > & & < / span > \
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< span class = "Constant" > \r< / span > m -f < span class = "Variable" > < span class = "Variable" > $< / span > toResource< / span >
< span class = "Keyword" > done< / span >
< span class = "Keyword" > done< / span >
< / pre >
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< ul >
< li > The < code > (/N)< / code > means to select only directory and not to crash if there isn’ t any.< / li >
< li > The < code > (.N)< / code > means to select only files and not to crash if there isn’ t any.< / li >
< li > The < code > :t< / code > means tail; if < code > toto=/path/to/file.ext< / code > then < code > ${toto:t}=file.ext< / code > .< / li >
< / ul >
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< p > After ⇒< / p >
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< pre class = "twilight" >
< span class = "Entity" > gif_to_png< / span > () { convert < span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > < span class = "Variable" > < span class = "Variable" > ${< / span > 1:r< span class = "Variable" > }< / span > < / span > .png < span class = "Keyword" > & & < / span > < span class = "Constant" > \r< / span > m -f < span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > }
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< span class = "Entity" > handle_resources< / span > () { map gif_to_png < span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > /resources/*.gif(.N) }
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map handle_resources /path/to/projects/*(/N)
< / pre >
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< p > No more bloc!
It might be a little bit harder to read if you’ re not used to functional programming notation.
But it is more concise and robusts.< / p >
< p > Another example with some tests.< / p >
< p > Find all files in project not containing an < code > s< / code > which their name contains their project name:< / p >
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< p > Before ⇒< / p >
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< pre class = "twilight" >
< span class = "Keyword" > for< / span > toProject < span class = "Keyword" > in< / span > Projects/*< span class = "Keyword" > ;< / span > < span class = "Keyword" > do< / span >
project=< span class = "Variable" > < span class = "Variable" > $< / span > toProject< / span > :t
< span class = "Keyword" > if< / span > print -- project < span class = "Keyword" > |< / span > grep -v s < span class = "Keyword" > > < / span > /dev/null
< span class = "Keyword" > then< / span >
print < span class = "Variable" > < span class = "Variable" > $< / span > project< / span >
< span class = "Keyword" > for< / span > toResource < span class = "Keyword" > in< / span > < span class = "Variable" > < span class = "Variable" > $< / span > toProject< / span > /*(.N)< span class = "Keyword" > ;< / span > < span class = "Keyword" > do< / span >
< span class = "Keyword" > if< / span > print -- < span class = "Variable" > < span class = "Variable" > ${< / span > toResource:t< span class = "Variable" > }< / span > < / span > < span class = "Keyword" > |< / span > grep < span class = "Variable" > < span class = "Variable" > $< / span > project< / span > < span class = "Keyword" > > < / span > /dev/null< span class = "Keyword" > ;< / span > < span class = "Keyword" > then< / span >
print -- < span class = "String" > < span class = "String" > " < / span > X < span class = "StringVariable" > < span class = "StringVariable" > $< / span > toResource< / span > < span class = "String" > " < / span > < / span >
< span class = "Keyword" > fi< / span >
< span class = "Keyword" > done< / span >
< span class = "Keyword" > fi< / span >
< span class = "Keyword" > done< / span >
< / pre >
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< p > After ⇒< / p >
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< pre class = "twilight" >
< span class = "Entity" > contain_no_s< / span > () { print < span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > < span class = "Keyword" > |< / span > grep -v s }
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function verify_file_name {
local project=< span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > :t
< span class = "Entity" > contains_project_name< / span > () { print < span class = "Variable" > < span class = "Variable" > $< / span > 1< / span > :t < span class = "Keyword" > |< / span > grep < span class = "Variable" > < span class = "Variable" > $< / span > project< / span > }
map < span class = "String" > < span class = "String" > " < / span > print -- X< span class = "String" > " < / span > < / span > < span class = "String" > < span class = "String" > $(< / span > filter contains_project_name < span class = "StringVariable" > < span class = "StringVariable" > $< / span > 1< / span > /*< span class = "String" > < span class = "String" > (< / span > .N< span class = "String" > )< / span > < / span > < span class = "String" > )< / span > < / span >
}
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map verify_file_name < span class = "String" > < span class = "String" > $(< / span > filter contain_no_s Projects/* < span class = "String" > )< / span > < / span >
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< / pre >
< p > Also, the first verstion is a bit easier to read.
But the second one is clearly far superior in architecture.
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I don’ t want to argue why here.
Just believe me that the functional programming approach is superior.< / p >
< p > Actually I lack the lambda operator.
If someone has an idea on how to create anonymous functions, just tell me, thanks.< / p >
< p > Here is the source code:< / p >
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< div class = "code" > < div class = "file" > < a href = "/Scratch/en/blog/Higher-order-function-in-zsh/code/functional.sh" > ➥ functional.sh < / a > < / div > < div class = "withfile" >
< pre class = "twilight" >
< span class = "Comment" > < span class = "Comment" > #< / span > !/usr/bin/env zsh< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > Provide higer-order functions < / span >
< span class = "Comment" > < span class = "Comment" > #< / span > usage:< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > < / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ foo(){print " x: $1" }< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ map foo a b c d< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > x: a< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > x: b< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > x: c< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > x: d< / span >
function map {
local func_name=< span class = "Variable" > < span class = "Variable" > $< / span > 1< / span >
shift
< span class = "Keyword" > for< / span > elem < span class = "Keyword" > in< / span > < span class = "Variable" > < span class = "Variable" > $< / span > @< / span > < span class = "Keyword" > ;< / span > print -- < span class = "String" > < span class = "String" > $(< / span > eval < span class = "StringVariable" > < span class = "StringVariable" > $< / span > func_name< / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > elem< / span > < span class = "String" > )< / span > < / span >
}
< span class = "Comment" > < span class = "Comment" > #< / span > $ bar() { print $(($1 + $2)) }< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ fold bar 0 1 2 3 4 5< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > 15< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > -- but also< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ fold bar 0 $( seq 1 100 )< / span >
function fold {
< span class = "Keyword" > if< / span > ((< span class = "Variable" > < span class = "Variable" > $< / span > #< / span > < span class = "Keyword" > < < / span > 2)) {
print -- < span class = "String" > < span class = "String" > " < / span > ERROR fold use at least 2 arguments< span class = "String" > " < / span > < / span > < span class = "Keyword" > > & 2< / span >
return 1
}
< span class = "Keyword" > if< / span > ((< span class = "Variable" > < span class = "Variable" > $< / span > #< / span > < span class = "Keyword" > < < / span > 3)) {
print -- < span class = "Variable" > < span class = "Variable" > $< / span > 2< / span >
return 0
} < span class = "Keyword" > else< / span > {
local acc
local right
local func_name=< span class = "Variable" > < span class = "Variable" > $< / span > 1< / span >
local init_value=< span class = "Variable" > < span class = "Variable" > $< / span > 2< / span >
local first_value=< span class = "Variable" > < span class = "Variable" > $< / span > 3< / span >
shift 3
right=< span class = "String" > < span class = "String" > $(< / span > fold < span class = "StringVariable" > < span class = "StringVariable" > $< / span > func_name< / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > init_value< / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > @< / span > < span class = "String" > )< / span > < / span >
acc=< span class = "String" > < span class = "String" > $(< / span > eval < span class = "String" > < span class = "String" > " < / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > func_name< / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > first_value< / span > < span class = "StringVariable" > < span class = "StringVariable" > $< / span > right< / span > < span class = "String" > " < / span > < / span > < span class = "String" > )< / span > < / span >
print -- < span class = "Variable" > < span class = "Variable" > $< / span > acc< / span >
return 0
}
}
< span class = "Comment" > < span class = "Comment" > #< / span > usage:< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > < / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ baz() { print $1 | grep baz }< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > $ filter baz titi bazaar biz< / span >
< span class = "Comment" > < span class = "Comment" > #< / span > bazaar< / span >
function filter {
local predicate=< span class = "Variable" > < span class = "Variable" > $< / span > 1< / span >
local result
typeset -a result
shift
< span class = "Keyword" > for< / span > elem < span class = "Keyword" > in< / span > < span class = "Variable" > < span class = "Variable" > $< / span > @< / span > < span class = "Keyword" > ;< / span > < span class = "Keyword" > do< / span >
< span class = "Keyword" > if< / span > eval < span class = "Variable" > < span class = "Variable" > $< / span > predicate< / span > < span class = "Variable" > < span class = "Variable" > $< / span > elem< / span > < span class = "Keyword" > > < / span > /dev/null< span class = "Keyword" > ;< / span > < span class = "Keyword" > then< / span >
result=( < span class = "Variable" > < span class = "Variable" > $< / span > result< / span > < span class = "Variable" > < span class = "Variable" > $< / span > elem< / span > )
< span class = "Keyword" > fi< / span >
< span class = "Keyword" > done< / span >
print < span class = "Variable" > < span class = "Variable" > $< / span > result< / span >
}
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Created: 09/28/2011
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Modified: 09/29/2011
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