At some point in its execution, the each method executes the yield instruction giving it an argument that happens to be the next element of the list in the case of the Array class's each method.

The function to retrieve the data from the first element of a list is called car (a name which is a holdover from an ancient assembly language instruction).

The instruction statement list was written down into PLC processor by entering instruction of "write down" through connecting computer with PLC processor by cable.