Re: [Haskell-cafe] how to make this work recursive ?

2 Mar 2015

      Richard A. O'Keefe schreef op 2-3-2015 om 0:59:
...
On 1/03/2015, at 11:17 pm, Roelof Wobben  wrote:
...
Now I have to find out how I can test if the LogMessage  has the text "this is not the right format" in it.
Well, the Haskell libraries include regular expression support.
At an elementary level, you can always do
is_prefix_of :: Eq x => [x] -> [x] -> Bool
is_prefix_of (x:xs) (y:ys) = x == y && is_prefix_of xs ys
is_prefix_of (x:xs) []     = False
is_prefix_of []     _      = True
is_infix_of :: Eq x => [x] -> [x] -> Bool
is_infix_of xs ys =
    xs `is_prefix_of` ys || (not (null ys) && xs `is_infix_of` tail ys)
"this is not the right format" `is_infix_of` aLogMessage
But it would be better if your LogMessage were not a string
but something structured where you did not have to go looking
for that text because you KNEW where to look for it.
I know where to look.

A LogMessage looks like this :

data LogMessage = LogMessage MessageType TimeStamp String
                 | Unknown String
   deriving (Show, Eq)

So if it's Unknown with a string then it will not be inserted into the 
MessageTree
The only thing I have to find out if  LogMessage contains this.

Roelof