upto ex. 5

exercises/Set3b.hs

@@ -77,7 +77,9 @@ sums i = sums' i 1
 --   mylast 0 [1,2,3] ==> 3
 
 mylast :: a -> [a] -> a
-mylast def xs = todo
+mylast def [] = def
+mylast def [x] = x
+mylast def (x:xs) = mylast def xs
 
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 -- Ex 4: safe list indexing. Define a function indexDefault so that
@@ -95,7 +97,9 @@ mylast def xs = todo
 --   indexDefault ["a","b","c"] (-1) "d" ==> "d"
 
 indexDefault :: [a] -> Int -> a -> a
-indexDefault xs i def = todo
+indexDefault [] i def = def
+indexDefault (x:xs) 0 def = x
+indexDefault (x:xs) i def = indexDefault xs (i-1) def
 
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 -- Ex 5: define a function that checks if the given list is in
@@ -111,7 +115,8 @@ indexDefault xs i def = todo
 --   sorted [7,2,7] ==> False
 
 sorted :: [Int] -> Bool
-sorted xs = todo
+sorted (x:y:xs) = (x <= y) && sorted (y:xs)
+sorted _ = True
 
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 -- Ex 6: compute the partial sums of the given list like this:
@@ -123,6 +128,7 @@ sorted xs = todo
 -- Use pattern matching and recursion (and the list constructors : and [])
 
 sumsOf :: [Int] -> [Int]
+sumsOf [] = []
 sumsOf xs = todo
 
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