Chris Kuklewicz wrote:
[snip]
There are other modules that come with Haskell than
Text.ParserCombinators.Parsec
such as
Text.ParserCombinators.ReadP
The solution with ReadP makes for a very short 'parse' function. Note that
reader is built in a recursive manner.
module Morse where
import Control.Monad(guard)
import Text.ParserCombinators.ReadP
parse = map fst . readP_to_S reader
where reader = done <++ choice (map pairToReader table)
done = look >>= guard . null >> return []
pairToReader (s,c) = string s >> fmap (c:) reader
table = (".-",'A'):
("-...",'B'):
("-.-.",'C'):
("-..",'D'):
(".",'E'):
("..-.",'F'):
("--.",'G'):
("....",'H'):
("..",'I'):
(".---",'J'):
("-.-",'K'):
(".-..",'L'):
("--",'M'):
("-.",'N'):
("---",'O'):
(".--.",'P'):
("--.-",'Q'):
(".-.",'R'):
("...",'S'):
("-",'T'):
("..-",'U'):
("...-",'V'):
(".--",'W'):
("-..-",'X'):
("-.--",'Y'):
("--..",'Z'):
[]
The table is sorted which means the result of 'parse' is in sorted alphabetical
order.
It also does not check which are dictionary words, so it finds many solutions:
*Morse> length $ parse "...---..-....-"
5104
*Morse> take 10 $ parse "...---..-....-"
["EEAGAEEEA","EEAGAEEEET","EEAGAEEIT","EEAGAEEU","EEAGAEIA","EEAGAEIET","EEAGAEST","EEAGAEV","EEAGAHT","EEAGAIEA"]
Thanks Chris, that's a neat solution and an eye opener for me -- I need
to investigate the Text package I think.
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