What does the “Just” syntax mean in Haskell?

It’s actually just a normal data constructor that happens to be defined in the Prelude, which is the standard library that is imported automatically into every module. What Maybe is, Structurally The definition looks something like this: That declaration defines a type, Maybe a, which is parameterized by a type variable a, which just means that you can …

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Prolog “or” operator, query

you can ‘invoke’ alternative bindings on Y this way: Note the parenthesis are required to keep the correct execution control flow. The ;/2 it’s the general or operator. For your restricted use you could as well choice the more idiomatic that on backtracking binds Y to each member of the list. edit I understood with …

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Meaning of *& and **& in C++

That is taking the parameter by reference. So in the first case you are taking a pointer parameter by reference so whatever modification you do to the value of the pointer is reflected outside the function. Second is the simlilar to first one with the only difference being that it is a double pointer. See …

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