cd-slash
Boolean expression pattern matching with tuples
I have a case clause (contrived for the purpose of this question):
level = 4
has_children_or_no_children = :no_children
case {level, has_children_or_no_children} do
{3, :has_children} ->
1
{4, :no_children} ->
2
_ ->
false
end
This works well. Normally though, with a single value in the case clause I can use a guard to match on greater than / less than integer values:
level = 4
has_children_or_no_children = :no_children
case level do
n when n < 5 ->
1
n when n > 0 ->
2
_ ->
false
end
Which again works well, but I can’t use these guard clauses inside the tuple passed to case in the first example:
level = 4
has_children_or_no_children = :no_children
# DOES NOT WORK
case {level, has_children_or_no_children} do
{n when n < 5, :has_children} ->
1
{n when n > 0, :no_children} ->
2
_ ->
false
end
Is there a way to perform a boolean test and a comparison with an atom simultaneously, to avoid having to nest case statements and duplicate the code to be executed?
Marked As Solved
sbuttgereit
The guard needs to be outside of the match:
case {level, has_children_or_no_children} do
{n, :has_children} when n < 5 -> 1
{n, :no_children} when n > 0 -> 2
_ -> false
end
3
Also Liked
nikolauska
You need to move the when outside the tuple and then it works
level = 4
has_children_or_no_children = :no_children
case {level, has_children_or_no_children} do
{n, :has_children} when n < 5 ->
1
{n, :no_children} when n > 0 ->
2
_ ->
false
end
2
cd-slash
Ahh that seems so easy (and nice) now that I see the solution! Thanks for your help ![]()
1
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