Possibly even more accessible: High school math. In a math exercise, when we state let A = 2 + 3π Then we can be dammed sure that for the rest of the exerci

Possibly even more accessible: High school math. In a math exercise, when we state let A = 2 + 3π Then we can be dammed sure that for the rest of the exercise, we can replace "A" by "(2 + 3π)" (and vice-versa) without ever introducing an error. Likewise, functions don't change A's value behind your back no matter what. Something in, something out, period. From there, you can explain function composition, how operators are actually binary functions, even types. We can go really far with just high school math: http://loup-vaillant.fr/tutorials/from-imperative-to-functional http://loup-vaillant.fr/tutorials/from-imperative-to-functio...