I know this sound very simple, but I failed to combine two strings into a new one.
The IO String "a" from a gtk entry is fetched by
a <- (entryGetText text_field)
The goal is to combine it like:
newstring = "Text: "+a
Any ideas to accomplish that? Thanks!
Using string concatenation:
do a <- entryGetText text_field
let b = "Text:" ++ a
return b
More simply:
do a <- entryGetText text_field
return $ "Text:" ++ a
You can play games too:
("Text:" ++) <$> (entryGetText text_field)
<$> is equivalent to `fmap` as infix operator. So what this does is that it takes the value out of the IO Monad (entryGetText text_field) and applies ("Text:" ++) to it.I believe that in Haskell, the string concatenation operator is ++.
String type is just a List of Chars, so ++ will also work on Strings. For example, "has" ++ "kell" returns "haskell".The very moment you use the assignment operator x <- expr with expr :: m a and m being some monad, x is not an m a but rather an a. In your case, the variable a has type String and not IO String, so you can concatenate it as you would do in pure code, e.g. "hello world " ++ a.
newstring <- fmap ("Text: " ++) $ entryGetText text_field