library(manipulate)
library(LearnBayes)

db=function(x,ab) dbeta(x,ab[1],ab[2])
pb=function(x,ab) pbeta(x,ab[1],ab[2])
manipulate(
  curve(pb(x, beta.select(list(p=.5, x=p.med), list(p=.9, x=p.90))),
        0, 1, main=paste("(a, b) =(",beta.select(list(p=.5, x=p.med), 
          list(p=.9, x=p.90))[1],",",
                         beta.select(list(p=.5, x=p.med), 
          list(p=.9, x=p.90))[2],")"), ylab = "CDF", xlab="P"),
  p.med = slider(0, 1, initial = 0.5),
  p.90 = slider(0, 1, initial = 0.9))