Tomasz Zielonka: ...
there are other reasons to box values besides implementing laziness, like for simplifying the memory model (which can simplify GC implementation), allowing to intermix values of different types (different kinds of polymorphism) or allow variable sized values (think strings, arrays and arbitrary size integers).
Some concrete examples: Arrays in many scripting languages, like Python, are often boxed. There are some languages, like R, where there are many types of unboxed arrays, for efficiency reasons.
There are nice unboxed arrays in Clean as well. The gain of efficiency is enormous. == Hmmm.... I thought that arrays in Python have no reason to be boxed. Lists, yes, since they are untyped, so they are arrays of pointers, but arrays are homogeneous. I don't know why boxing may simplify the *memory model*. The most dramatic effect of implicit boxing is the possibility - available in Smalltalk - to change the *identity* of an object. You write (x become y), and all references to the object assigned to x, point now to something completely different. A terrible weapon. Jerzy Karczmarczuk