Identifying a specific index in a list of strings and removing everything in the list beyond that index in Haskell -

i've started learning haskell, , i've encountered problem can't seem overcome.

my input list of strings contain 3 characters each. want split list @ point , have output list until point.

example:

main> listsplitter ["aaa", "bbb", "ccc", "stp", "ddd"] main> ["aaa", "bbb", "ccc"] main> listsplitter ["aaa", "stp", "bbb", "ccc", "ddd"] main> ["aaa"] 

where stp in case identifying string @ stop output string.

if it's possible split string in similar way, or perhaps easier, useful. list of strings further problem i'm working on string. this:

main> stringsplitter "aaabbbcccstpddd main> "aaabbbccc" main> stringsplitter "aaastpbbbcccddd" main> "aaa" 

i should mention achieve without importing data modules.

thanks time!

the solution first question has 2 parts:

1. finding takewhile function
2. writing predicate use takewhile, once you've found it

for (1), try searching hoogle [a] -> [a], not full type signature want part of it, , scrolling through matches; find takewhile before long.

for (2) want involving (==) or perhaps (/=). playing around bit may come with:

keep :: string -> bool keep x = x /= "stp" 

and can simplify using partial application instead:

keep :: string -> bool keep = (/= "stp") 

finally combine parts (1) , (2):

listsplitter :: [string] -> [string] listsplitter = takewhile (/= "stp") 

to solve second problem, of stringsplitter, can't use takewhile, because can @ 1 item @ time, , need @ more. there elegant way using data.list and/or data.list.split (exercise: find elegant way), quite easy implement recursively pattern matching starting head of list:

stringsplitter :: string -> string stringsplitter [] = [] stringsplitter ('s':'t':'p':_) = [] stringsplitter (x:xs) = x : stringsplitter xs