This implements just a few basic lens-like concepts to ease state updates. Similar to fclabels in approach, just without the extra dependency.

We don't include an explicit export list because everything here is meant to be exported.

Short synopsis: --------------- @ f :: Idris () f = do -- these two steps: detaggable <- fgetState (opt_detaggable . ist_optimisation typeName) fputState (opt_detaggable . ist_optimisation typeName) (not detaggable)

• - are equivalent to: fmodifyState (opt_detaggable . ist_optimisation typeName) not
• - of course, the long accessor can be put in a variable;
• - everything is first-class let detag n = opt_detaggable . ist_optimisation n fputState (detag n1) True fputState (detag n2) False
• - Note that all these operations handle missing items consistently
• - and transparently, as prescribed by the default values included
• - in the definitions of the ist_* functions.
• -
• - Especially, it's no longer necessary to have initial values of
• - data structures copied (possibly inconsistently) all over the compiler. @