Stacks and queues

In 1961 Edsger Dijkstra described how a compiler could turn an arithmetic expression such as 3 + 4 × 2 into an order a machine can evaluate. His method sent operators into a holding track, like wagons in a railway shunting yard, and released them when an operator of lower priority arrived. It is still called the shunting-yard algorithm.

The holding track was a stack. The same structure keeps track of function calls in every running program, powers the Undo button and checks that your brackets match.