library(SuppDists)
jdist<-list(gamma=-0.7, delta=0.8, xi=26, lambda=1.4, type="SU")
xvals<-seq(10,60,by=1)
yvals<-dJohnson(xvals,jdist)
plot(xvals,yvals,col="blue",type="l")

#this is some trial observation - say we see an observation of "40" and give it a weighting of one-third
observation<-40
observationweight<-1/3

#your code here - modifies jdist for example
jdist<-list(gamma=-0.6, delta=0.7, xi=27, lambda=1.5, type="SU")
#

xvals<-seq(10,60,by=1)
yvals<-dJohnson(xvals,jdist)
lines(xvals,yvals,col="red")