Depends on what kind of response you want to send. HTML? JSON (Poison makes that trivial then)? Etc…?
You could map over them.
For a sum function instead of specific arguments I’d probably pass them in as an array, like:
http://localhost:4000/sum?input[]=10&input[]=12&input[]=20
Which would output whatever 10+12+20 is or so (via Enum.reduce over the list). You really only need specific named args if order or names matter, which for a sum it would not. 
I am thinking along the lines of PHP’s print_r or function, dpr if you are familiar with Drupal. It is more like PHP’s explode although the type may be more complicated. Do you know of some samples?
I’ve got an awful let to learn.
This project is my very first Elixir project and I am learning Elixir as I go along. I am trying not to make the mistake I made years ago with Ruby on Rails, when I tried learn RoR without knowing Ruby well enough first and abandoned it, but it Elixir looks much simpler and it may be the docs.
Well inspect/1 converts anything to something as a readable string, and IO.inspect/1 does that while also printing it to the standard out, you might want inspect/1 if you are just dumping it back though?
Now for tough map question.
If I have to handle an unknown number of query parameters how would I handle that?
Say the query parameters are ?a=1&b=2?c=3?d=“apple”?e=5 etc?
What I would like to do is to list each parameter and its type then sum the numeric ones,
so in this instance the output would
| param | value | type |
|-------|-------|--------|
| a | 4 | number |
| b | 2 | number |
| c | 3 | number |
| d | apple | string |
| e | 5 | number |
| sum | 11 | number |
So given those param’s and values (remember that the web browser only gives you strings, so you do not know if they can be parsed as numbers yet, you basically get them from the browser like %{"a" => "4", "b" => "2", "c" => "3", "d" => "apple", "e" => "5", "sum" => "11"}) and they are in the params argument to your routed function, then could do something like this:
# parse integers out if possible, else keep as strings
params =
params
|> Enum.map(fn {k, v} ->
v =
case Integer.parse(v) do
{i, ""} -> i
_ -> v
end
{k, v}
end)
# Add up the numbers:
summed =
Enum.reduce(params, 0, fn
({_, i}, acc) when is_int(i) -> i + acc
(_, acc) -> acc
end)
# And you can format the output however you want to...
summed =
Enum.reduce(params, 0, fn
(i, acc) when is_int(i) -> i + acc
(_, acc) -> acc
end)
In this code can I assume that (_,acc) refers to an empty params list?
What is the difference between if/case/cond and when?
Enum.reduce is being passed an anonymous function with two function clauses - each function head matching a different pattern.
(i,acc) when is_int(i) -> i+ acc
is the first function clause - when starts the guard clause of the pattern, checking the type of i (with the built-in-function (BIF) is_int/1) - so if i is an integer, this function clause will evaluate to i + acc.
(_,acc) -> acc
is the next function clause where the head gets a chance to match if the previous head matches failed - the _ (underscore) simply indicates that you don’t care about that value - this function clause will simply evaluate to the acc value without further modification.
@peerreynders described it right.
I also forgot it was in a tuple in the above example, fixed up my post. ^.^;
When is the when keyword used? The docs page for case, cond, and if doesn’t explain the when keyword, ie where it is preferable to if,case or cond?
Guard clauses are introduced with case.
But they work the same way with function heads (which is why I consider them part of the pattern in those scenarios).
I like this succinct quote
Pattern matching is a conditional construct and destructuring isn’t.
I’d consider if and unless “covenience”/“familiarity” macros. case is driven by the power of pattern matching, while cond is about “truthiness” - if there are alternatives then there must be at least two separate expressions (i.e. not statements).