What are practical guidelines for evaluating a language's “Turing Completeness”?

Question

I\'ve read \"what-is-turing-complete\" and the wikipedia page, but I\'m less interested in a formal proof than in the practical implications of being Turing Complete.

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Answer 1

Brainfuck is Turing complete, and has only loop structures and memory incrementation/decrementation so this is enough.

On the other hand there is no way to modify any value in the lambda calculus, but it is Turing complete, so it it is clearly possible to do it without mutable memory.

Most likely you program has nothing to do with the lambda calculus though, so for a practical answer the minimum must be

1. A way to write to a variable
2. A way to read to a variable
3. A form of conditional goto (if statement, while loop, etc)