x = expression; (i.e. the assignment of the result of an expression to a variable) clearly calls for the expression to be evaluated and the result is placed in x, but what actually is in x is irrelevant until there is a need for its value via a reference to x in some later expression whose evaluation could itself be deferred, though eventually the rapidly growing tree of dependencies would be pruned to produce some symbol rather than another for the outside world to see.

Lazy evaluation