MBS yaml

library(yaml)
library(data.tree)
yaml <- "
functions:
  currbalfun: |
    function(node) {
      Aggregate(deal, 'currbal', function(bal) sum(bal, na.rm = TRUE))
    } 
  
TC_1:
  principaldesc: PT
  interestdesc: FIX
  coupon: 6.50
  factor: 1
  AF:
    cusip: 3136AS4X1
    principaldesc: PT
    interestdesc: FLT
    coupon: 0.95
    origbal: 38400349
    factor: 1
    currbal: 38400349
    index: LIBOR1BBA
    cap: 6.50
    floor: 0.50
    multiplier: 1
  AS:
    cusip: 3136AS4Y9
    principaldesc: NTL
    interestdesc: INVIO
    coupon: 5.55
    origbal: 38400349
    factor: 1
    currbal: 38400349
    index: LIBOR1BBA
    cap: 6.00
    floor: 0
    multiplier: -1
TC_2:
  principaldec: PT
  interestdesc: FIX
  coupon: 6.50
  AB:
    cusip: 3136AS4Z6
    principaldesc: PACAD
    interestdesc: FIX
    coupon: 3.00
    origbal: 63959530
    factor: 1
    currbal: 63959530
    index: none
    cap: 0
    floor: 0
    multiplier: 0
  AV:
    cusip: 3136AS5A0
    principaldesc: PACAD
    interestdesc: FIX
    coupon: 3.0
    origbal: 3456470
    factor: 1
    currbal: 3456470
    index: none
    cap: 0
    floor: 0
    multiplier: 0
  AZ:
    cusip: 3136AS5B8
    principaldesc: PACAD
    interestdesc: FIX
    coupon: 3.0
    origbal: 8584874
    factor: 1
    currbal: 8584874
    index: none
    cap: 0
    floor: 0
    multiplier: 0
  ZA:
    cusip: 3136AS5C6
    principaldesc: SUP
    interestdesc: ACC
    coupon: 3.00
    origbal: 20000000
    factor: 1
    currbal: 20000000
    index: none
    cap: 0
    floor: 0
    multiplier: 0

"


lol <- yaml.load(yaml)
deal <- as.Node(lol, nodeName = "Deal")

evaluator <- function(fctnode) {
  for (fnct in fctnode$fields) {
  
    f <- eval(parse(text = fctnode[[fnct]]))
    # warp the function and call using node
    f2 <- function() {
      f(fctnode$parent)
    }
    fctnode$parent[[fnct]] <- f2
  }
}


deal$Do(fun = evaluator, 
        filterFun = function(node) node$name == "functions")

do.call(print, c(deal, deal$fieldsAll))