Nice to see you back on the List!
It is meant for people who remember the Lua standard library more than
the more obscure utilities, like 'cut' etc. For what we might call
'personal automation' :) It is also a very expressive calculator...
I once toyed with a slightly related idea - I had a series of nontrivial formulas and wanted to see how the output reacts to changing inputs. It was unfortunately more than 2 inputs so "graphing it in Excel" was out of the question. But the interactivity of Excel left me wondering, if something like this can be implemented as a REPL with Lua formulas.
The base idea was to (ab)use metatables with __[new]index on _G to construct an AST on the fly from the formula being entered, with two "types" - var{} and exp{...}, and store their values as a "snapshot" that gets re-evaluated with all dependent exp-s at every input. So basically you could say 'a = 1; b = sin(a*math.pi); c=math.sqrt(b)' and later on every time you change 'a' you can also see 'b' and 'c' changing simultaneously. Unfortunately due to the way Lua is implemented, comparisons (<, ==, ~=) can't be "virtualized", but this was enough for my case.
Implementation is left as an exercise to the reader :)
