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help with tutorial example - recursive summing and multiplication of list
f#tutorial

i have just started with f# so my knowledge is very limited....i was attempting to modify an example in the tutorial created in vs2008 - it's a project type...

i am running it in a script file interactively. the code sums a list

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let rec SumList xs =
    match xs with
    | []    -> 0
    | y::ys -> y + SumList ys

SumList [1;2;3;4;5]

this works as expected

but when i change to 

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let rec SumList xs =
    match xs with
    | []    -> 0
    | y::ys -> y * SumList ys

SumList [1;2;3;4;5]

i get 0 as the answer....

my intent is to multiply the values in the list rather than sum them.....the simple changing of the operator produces a 0 which is not my intent.....

looking for help on what i am sure is a very simple error and misunderstanding on my part.....

i am sure that a 0 is introduced somewhere in the list but i don't get where or why....

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| [] -> 1

When xs = [5] you'll have 5 * SumList [], and you've defined SumList [] to be 0.

By on 2/28/2010 8:59 PM ()

well somethimes it is advisable to know syntax better and dig deep before pulling a help trigger.....

the solution is very simple if you know what the -> operator is...

this version works with the only drawback being that the [] set returns 1...could be ok since 0! = 1....

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let rec SumList xs =
    match xs with
    | [] -> 1
    | y::ys -> y * SumList ys
By on 2/28/2010 8:56 PM ()

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