When thinking in a functional mindset, given that functions are supposed to be pure, one can conclude any function with no arguments is basically just a value. However,
I think what you want is lazy.
let resource = lazy( // expensive value init here )
Then later when you need to read the value...
resource.Value
If you never call the Value property, the code inside the lazy block never gets run, but if you do call it, that code will be run no more than once.
lazy