Hello,
I am learning picolisp and in the context of solving an exercise (from
Advent of Code 2020) I have stumbled upon this question.
Given an input file named 5.input with contents:
BFFFBBFRRR
FFFBBBFRRR
BBFFBBFRLL
Say I read the contents into a list with e.g.
: (in "5.input"
(make
(until (eof)
(let (s (line T))
(when s (link s))))))
-> ("BFFFBBFRRR" "FFFBBBFRRR" "BBFFBBFRLL")
Next step is, I want inside picolisp to read not the file directly,
but through a preprocessing step with the program tr, i.e. what in the
shell would be
$ tr FBLR 0101 < 5.input # or cat 5.input | tr FBLR 0101
1000110111
0001110111
1100110100
And finally I want to add one more preprocessing step, sorting, like
$ tr FBLR 0101 < 5.input | sort # or cat 5.input | tr FBLR 0101 | sort
0001110111
1000110111
1100110100
I have not come very far. I know that using (in ... ) I can replace
the file "5.input" with '(cat "5.input") and get the same result, but
instead the attempt to replace i
t with e.g. '(tr "FBLR" "0101" "<" "5.input") fails with:
usage: tr [-Ccs] string1 string2
tr [-Cc] -d string1
tr [-Cc] -s string1
tr [-Cc] -ds string1 string2
-> NIL
And so do other attempts at various combinations of (pipe ...), (in
..), (exec ...) etc.
Is there a way to do this and get the result:
-> ("0001110111" "1000110111" "1100110100")
?
Regards,
Christos Gitsis
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