Huazhi (Hank) Gong wrote:
Like given a string list s="This is the string I want to test", I want to get the substring. In ruby or other language, it's simple like s[2..10], but how to do it in Haskell?
Quite simply, actually:
infixl 1 %% str %% idxs = map (str !!) idxs
That is it. Not the most efficient, but gets the job done.
tstring = "This is the string I want to test" test1 = tstring %% [2..10]
*Sub> test1 "is is the"
However, like I want to choose s[1,3,6,10] or something like this. Are there some straightforward function or operator for doing this job?
Yes, see above.
test2 = tstring %% [1,3,6,10]
*Sub> test2 "hsse" Indices don't have to be in the increasing order
test3 = tstring %% [10,6,3,1]
*Sub> test3 "essh" or in any order...
test4 = tstring %% [10,6,3,1]++[2..10]
*Sub> test4 "esshis is the" Of course if one cares about the overhead of running code (rather than the overhead of writing code), one would probably ask, as several posters did, if the list of characters is the right data structure and if the problem indeed calls for random access to the elements of the list.