CODEWITHSUNDEEP
listerlang
user1945673
user1945673

Reputation: 15

Adding improper tail to given Erlang list

How do I add an improper tail (e.g. |<<>>) to a proper Erlang list "Parent" with an arbitrary number of elements? I need this to create a range scan upper limit value for matchspecs on a MNESIA table where list keys represent object hierarchy. To my understanding (inspired by the sext project) any children of a parent key Parent=[T1,T2,T3] (T1,T2,T2 are arbitrary Erlang Terms) can be found with matchspecs asking for:

Child > [T1,T2,T3] and Child < [T1,T2,T3|<<>>]

Given only Parent as a whole, how do I calculate the upper value?

Upvotes: 1

Views: 89

Answers (1)

Steve Vinoski
Steve Vinoski

Reputation: 20014

To get the improper list you're looking for, just append the empty binary <<>> to the list:

Parent ++ <<>>.

For example, if Parent is [t1,t2,t3]:

1> Parent = [t1,t2,t3].
[t1,t2,t3]
2> Parent ++ <<>>.
[t1,t2,t3|<<>>]

Upvotes: 3

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