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HackerRank tells you all you need to know about the input, so it's a completely different situation from an arbitrary CLI. This approach works for the type of problems on this particular site, and for the typical use case where input comes from a terminating program or a file.

It actually won't run forever because of a handy thing called EOF.

I'm a Haskell newbie and reading input data is the most difficult part of the problem for me. I don't see where your code structures the input data into the "grouping" required in this task.

I mean, how is the function "run" (if I understood at least that part) supposed to get T, and then, for 1..T, the value of N and the list of (x,y) as required for this problem? (I understand that we could simply "skip" the initial T but then (until EOF is reached) definitely need to get the N in order to know how many lines (x,y) we must read -- where am I wrong?)

I'm keen to switch from imperative to functional programming, but as far as the "I/O" is concerned, the problem statement "there are T test cases and for each test case..." already contains the declarative "for". And I'd like to write a function that receives a vector of N pairs (x,y), but how to get there without doing "for i in 1..N: read [x, y] and append to the list L" ?

## Functions or Not?

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Thx! This is helpful. All this IO stuff was getting pretty ugly :)

That's still ugly, IMO. Here's my runner:

From run, you can just work with pure functions like the Haskell gods intended.

how do you know how many lines to read? In a situation where a user is inputting a variable set of inputs, would this work?

If you run this it will just ask for inputs forever.

also, I think that you don't need to define your own read if your run function has a definition

`run :: [Int] -> [String]`

HackerRank tells you all you need to know about the input, so it's a completely different situation from an arbitrary CLI. This approach works for the type of problems on this particular site, and for the typical use case where input comes from a terminating program or a file.

It actually won't run forever because of a handy thing called EOF.

Nice idea about the type sig, though.

how would you write

on one line?

I'm a Haskell newbie and reading input data is the most difficult part of the problem for me. I don't see where your code structures the input data into the "grouping" required in this task.

I mean, how is the function "run" (if I understood at least that part) supposed to get T, and then, for 1..T, the value of N and the list of (x,y) as required for this problem? (I understand that we could simply "skip" the initial T but then (until EOF is reached) definitely need to get the N in order to know how many lines (x,y) we must read -- where am I wrong?)

I'm keen to switch from imperative to functional programming, but as far as the "I/O" is concerned, the problem statement "there are T test cases and for each test case..." already contains the declarative "for". And I'd like to write a function that receives a vector of N pairs (x,y), but how to get there without doing "for i in 1..N: read [x, y] and append to the list L" ?