[Jprogramming] Fold -- can't get it to work

[Xiao-Yong Jin]

> On Jul 2, 2020, at 3:18 PM, Piet de Jong <pietdion at gmail.com> wrote:
> 
> My issue is not with x and y insofar as (u F:. v) is concerned.   I agree it  makes sense for x to be 'control information/initial condition' and y the ’data’.
> 
> My concern is with x and y insofar as v is concerned.    Each item in y for  the verb (u F:. v) now becomes x for the verb v.    So the data items y become x’s from v’s point of view.  

It's consistent with the existing primitives.

   ]F.:(+([[[:echo;)'=';[;'+';]) i.4
┌─┬─┬─┬─┬─┐
│5│=│2│+│3│
└─┴─┴─┴─┴─┘
┌─┬─┬─┬─┬─┐
│6│=│1│+│5│
└─┴─┴─┴─┴─┘
┌─┬─┬─┬─┬─┐
│6│=│0│+│6│
└─┴─┴─┴─┴─┘
6
   (+([[[:echo;)'=';[;'+';])/i.4
┌─┬─┬─┬─┬─┐
│5│=│2│+│3│
└─┴─┴─┴─┴─┘
┌─┬─┬─┬─┬─┐
│6│=│1│+│5│
└─┴─┴─┴─┴─┘
┌─┬─┬─┬─┬─┐
│6│=│0│+│6│
└─┴─┴─┴─┴─┘
6