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Sure it is useful to run code in your head. I didn't say we must not think through code.

But to unable to run actual code at all? Come on. Who learns programming that way?

I don't think anyone suggested that.

I suggested that. You should be able to look at algorithmic code and prove it correct without worrying about running it.

> But to unable to run actual code at all? Come on. Who learns programming that way?

Edsger Dijkstra was a proponent of that approach i.e. develop program and proof by hand in a language for which there is no compiler/interpreter.