base 2147483648
ditch-empty-list [bool] [popd] [pop] ifte
bool_to_int [0] [1] branch
uncons-two [uncons] ii swapd

add-with-carry _add-with-carry0 _add-with-carry1
_add-with-carry0 [bool_to_int] dipd + +
_add-with-carry1 base [mod] [>=] clop

add-carry-to-digits [_actd_P] [_actd_THEN] [_actd_R0] [_actd_R1] genrec
_actd_P pop not
_actd_THEN popd
_actd_R0 [bool] [_actd_R0.then] [_actd_R0.else] ifte
_actd_R0.else popd 1 false rolldown
_actd_R0.then 0 swap uncons [add-with-carry] dip
_actd_R1 i cons

add-digits initial-carry add-digits'
initial-carry false rollup
add-digits' [P] [THEN] [R0] [R1] genrec
P [bool] ii & not
THEN [P'] [THEN'] [ELSE] ifte
R0 uncons-two [add-with-carry] dipd
R1 i cons
P' [bool] ii |
THEN' ditch-empty-list add-carry-to-digits
ELSE pop swap [] [1 swons] branch


add-bigints 
[[first] ii =]                       # are they the same sign?
[[uncons] dip rest add-digits cons]  # add the digits and set the sign.
[neg-bigint sub-bigints]             # adding unlikes is actually subtraction.
ifte