[R] Plotting several functions in the same display (again)

[Julio Sergio]

To superimpose two functions plots in the same page. The functions L0 
and L1, as defined below, I use the following code:

  # An accumulative normal distribution function with
  # several parametres
  f0 <- function(mu, xm, ds, n) { 
    1 - pnorm((xm-mu)/(ds/sqrt(n))) 
  } 

  f1 <- function(mu,n) f0(mu, 386.8, 48, n) 

  # Two functions with just the parameter mu
  L0 <- function(mu) f1(mu, 36) 
  L1 <- function(mu) f1(mu,100) 
  plot(L0,ylim=c(0,1),xlim=c(360,420)) 
  curve(L1,add=T) 

However, I'm puzzled with a problem in the same line: When I passed a 
"function producer" to plot, again it worked well; however it didn't work in 
the same way when trying to use this same argument in curve. See what I'm 
talking about:

  # A particular normal distribution function: 
  dn8 <- function(z,m) dnorm(z,m,8) #  norm dist with sd=8

  # A function that produces functions:
  #   returns a function such that given a mean(i) depends only
  #   on z
  fi <- function(i) function(z) dn8(z,i)

  plot(fi(370),xlim=c(360,420)) # Works well!

  curve(fi(380),add=T) # This doesn't work 

  # However, if I put it in this way, surprisingly, it works!
  ff <- fi(380)
  curve(ff,add=T)

I cannot understand this behaviour. Could anyone give me some feedback on 
this?

Thanks,
 -Sergio.