A *(topic) for programming languages, a *(term) for computational _(language)s that are at least as _(expressive|expressiveness) as the _(lambda calculus).

Actually, a proper definition would require Turing-machine equivalence, but lambda calculus suffices for non-interacting machines and computations that should halt <em>(but what good are those?)</em>. However, not all languages listed here, like C, are sufficiently expressive, but a good enough approximation in practice, once supplemented with proper libraries.

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Lambda calculus is turing complete.  Here is an example of a program that will run forever in lamba calculus, using \ for lambda.

(\x. x x)  (\x. x x)

When the term on the right is substituted into the term on the left it yields the original program.

A turing machine is a non-interacting machine.  A turing machine program can either halt or run forever - it cannot interact with the outside world.
