Nesting
Nesting seems to be The Answer to everything in software.
We conquered flat assembler programming with Structured Programming - basically drawing a box around a piece of code.
We conquered “global variables” with scoping - another word for nesting.
OO gave us nesting of data. (But, OO does not provide nesting of control flow, in fact OO spaghettifies control flow (overriding, inheritance))
FP lambdas (1st class functions) use The Stack to create dynamic, shared, nesting chains.
Flowcharts nest control flow, but do not nest data.
StateCharts nest control flow (and, flags, and, “the state explosion problem”).
In ASCII, we represent nesting using { ... } and function definitions (local variables are nested inside functions).
We draw boxes around code using ASCII instead of using 2D graphics.
We draw flat pictures of trees. These often represent nested structures, like Russian Dolls. A “node” “below” another “node” is a representation of the node contained in the other node.
[Containment === nesting].
Parsing, unlike REGEX, can deal with nested text.
PEG parsing can match balanced parentheses (actually, balanced anything).
This kind of parsing allows us to get away even longer using ASCII Art to represent nested languages.
observation: Nesting is needed only when the program does not fit in an eye-full (e.g. an editing window) ; corollary - we don’t need nesting when code is only 5 lines long (in fact, global variables are not even a problem at that scale (in functional notation, lack-of-nesting is called “free variables”))