Problem Statement

A problem posed by Paul Graham is that of creating a function that takes a single (numeric) argument and which returns another function that is an accumulator. The returned accumulator function in turn also takes a single numeric argument, and returns the sum of all the numeric values passed in so far to that accumulator (including the initial value passed when the accumulator was created).

The detailed rules are at http://paulgraham.com/accgensub.html and are reproduced here for simplicity (with additions in small italic text).

Create a function that implements the described rules.

It need not handle any special error cases not described above. The simplest way to implement the task as described is typically to use a closure, providing the language supports them. Where it is not possible to hold exactly to the constraints above, describe the deviations.

Let's start with the solution:

\ RossetaCode 'accumulator factory'

\ The 'accumulate' word stores the accumulated value in an array, because arrays
\ are mutable:
: accumulate \ n [m] -- n+m \ [m] -> [n+m]
  a:pop rot n:+
  tuck a:push swap ;

\ To comply with the rules, this takes a number and wraps it in an array, and
\ then curries it.  Since 'curry:' is "immediate", we need to postpone its
\ action using 'p:.

: make-accumulator
  1 a:close 
  ' accumulate 
  p: curry: ;

\ We 'curry' the initial value along with 'accumulate' to create
\ a new word, '+10', which will give us the accumulated values
10 make-accumulator +10

\ This loop will add 1, then 2, then 3, to the accumulator, which prints the
\ results 11,13,16:
( +10 . cr ) 1 3 loop 
bye