Infographic 07 · D3 · Aliens block

One argument, one host

The eleven lines never change. The argument does, and that is the entire reason a function is worth having. Watch the same call fired three times.

A call, an attach, the work, and the endscrub the beats

The function box is drawn once and never redrawn, because the claim of the diagram is that it does not change. Beat four is the one people skip: the traveller fades, and nothing it touched keeps state after the call returns.

The four beats

#	Beat	What it means
01	The call	one argument, handed over at the door
02	The attach	exactly one host, and it was named
03	The work	same eleven lines, a different outcome
04	The end	nothing of it outlives the call

Three calls

Argument	Outcome	Note
`fmt="json"`	one JSON document	Same eleven lines. The argument decided the shape.
`fmt="csv"`	one CSV file	Nothing about the function changed between these two.
`fmt="parquet"`	one Parquet part	A parameter is the seam a caller is allowed to move.

This is the diagram behind campaign day 78, the first of the five-day Aliens block. The written piece is in the writing index.