dummy key-value list in J language

h.ijs

cocurrent 'H'

fst =: [: > 0&{
snd =: [: > 1&{
nop =: ''"_

pos =: 1: i.~ [: ; (([: # ]) = [: +/ (] = [: fst [) :: 0:) each
add =: ;~
unsafe_get =: [: snd ([: > [) {~ pos
get =: (unsafe_get <) :: nop
unsafe_set =: 4 : '(<y) (x pos <fst y) } x'
set =: unsafe_set :: add

cocurrent 'base'

NB. usage example
NB.    h =: ('two' ; 2) ; ('zero' ; 0) ; (<'one' ; 1)
NB.    h get 'one'
NB. 1
NB.    $h =: h set ('one';111)
NB. 3
NB.    h get 'one'
NB. 111
NB.    $h =: h set ('five';5)
NB. 4
NB.    h get 'five'
NB. 5