Question

So I have the following list of tuples and a string

type M a = [(String, String)]
m = [
    ("x", "a car"),
    ("y", "a animal")
]
s = "this is x and y"

I am trying to

strRep m s => “this is a car and a animal”

So this is my attempt so far

import Data.List.Utils

strRep :: (Show a) => M -> String -> String
strRep [] s = s
strRep (m:ms) s = replace (fst m) (snd m) s : strRep ms s

The above code returns a list of string. I cant quite figure out the proper way to do loop here.

Answer 1

I’m not sure where replace is coming from in your example above. But… assuming it exists, and does what you expect, you should be able to remove the cons (:) from your strRep function, and instead pass the result of replace into the next run of strRep, like so:

strRep :: (Show a) => M -> String -> String
strRep [] s = s
strRep (m:ms) s = strRep ms (replace (fst m) (snd m) s)

Now, instead of returning a list of strings, each a version with one thing replaced. You are iteratively replacing each string, passing the new strings on for the next replacement.