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Use map to process list of lines from stdin?
Posted: Tue Dec 11, 2012 9:57 pm
by t3o
hi,
I am new to newlisp and I managed to read and process lines from stdin this way:
Code: Select all
(while (read-line)
(println (slice (current-line) (div (length (current-line) ) 2)))
)
= print half of each line. A friend needed that.
I would like to do this by calling a function for each line of input but I cannot get it running. I thought of something like this:
Code: Select all
(map (fn(line)
(println ..)
(read-line)
)
What is wrong with that?
Thanks
t3o
Re: Use map to process list of lines from stdin?
Posted: Wed Dec 12, 2012 1:42 am
by jopython
Nothing wrong with that.
But map is for transforming a list into a different one based on the function you apply.
You are throwing away the transformed list by just using a print function.
Re: Use map to process list of lines from stdin?
Posted: Wed Dec 12, 2012 9:48 am
by cormullion
To get a line of input, you use
(current-line), which returns a string. However,
map applies a function to a list (as jopython says), rather than to a string. It's not clear whether you want to apply a function to each line, or to map a function over a list of every character in the current line.
For example, if you wanted to use
map to print the integer code of each character, do this:
Code: Select all
(while (read-line)
(map
(fn (character)
(print (char character)))
(explode (current-line)))
(println)
)
Notice that the anonymous function 'character' (which prints the integer code of a character) is applied to every item in the list of characters produced by
(explode (current-line)).
Re: Use map to process list of lines from stdin?
Posted: Sat Dec 15, 2012 9:58 pm
by t3o
hi and thanks for your answers!
My fault (or one of mine) was to think a call to "read-line" would result in a list of lines that I could process with "map": I wanted to map a shrink function on each of the lines.
Now I know that a call to "read-line" results in only a single line read. Hence its name ;-)
Is the code below the best (shortest; most newlispish) solution for my problem to print only a half of each line of input?
Code: Select all
#!/usr/bin/newlisp
(while (read-line)
(println (slice (current-line) (div (length (current-line) ) 2)))
)
; echo -e "foofoo\nblabla\n"| ./echo.lsp
thanks
t3o
Re: Use map to process list of lines from stdin?
Posted: Fri Dec 21, 2012 2:47 pm
by William James
Code: Select all
(define (half-string str)
((div (length str) 2) str))
(while (read-line)
(println (half-string (current-line))))