Recursive function and stopping condition in Haskell

Question

I am implementing a recursive function and I want the stopping condition be (2*scope) which is parameter to function

sortByManhattanDistance agent (2*scope) scope xs sortedNearFoodList = sortedNearFoodList

sortByManhattanDistance agent n scope xs sortedNearFoodList = sortByManhattanDistance agent (n+1) scope xs (sorted ++ sortedNearFoodList) 
where sorted=compareManhattanDistance xs agent n

and hugs complain that: Syntax error in declaration (unexpected symbol "*") Does it mean that I cannot use some function on parameters?

thanks in advance

You can't use (2*scope) as a input argument value. That is not a valid syntax — ДМИТРИЙ МАЛИКОВ
– ДМИТРИЙ МАЛИКОВ, Commented Mar 31, 2013 at 12:28

dave4420 · Accepted Answer · 2013-03-31 12:29:31Z

5

No, you cannot use functions or operators on the left hand side of an equation like that.

The proper way to do what you want is to use guards:

sortByManhattanDistance agent n scope xs sortedNearFoodList
    | n == 2 * scope = sortedNearFoodList
    | otherwise      = sortByManhattanDistance agent (n+1) scope xs
                                            (sorted ++ sortedNearFoodList) 
  where sorted = compareManhattanDistance xs agent n

answered Mar 31, 2013 at 12:29

dave4420

47.2k6 gold badges121 silver badges153 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

nurgasemetey Over a year ago

i forgot about this! your advice was very useful

Collectives™ on Stack Overflow

Recursive function and stopping condition in Haskell

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related