r - ggplot2 syntax for geom_smooth -

i have following function using fit non linear curve set of data. keep receiving following error:

error in do.call("layer", list(mapping = mapping, data = data, stat = stat,  :   object 'y' not found  

the error coming geom_smooth fit. can offer suggestions?

below test data , function:

library("ggplot2")   df <- data.frame(rfp_fold=1:20, e=rnorm(20))    flimplot <- function(data) {     ggplot(data, aes(x=rfp_fold, y=e)) +     geom_point(shape=1) +     geom_smooth(method=nls,                     # add non linear regression fit             formula='y ~ * (x / (x + k))',    # forumla fit             start=list(a=max(y), k = 0.1),  # set parameters             se = false,         # no shaded ci             fullrange=true)    # extend regression line    }  flimplot(df)  # error in do.call("layer", list(mapping = mapping, data = data, stat = stat,  :  object 'y' not found  

i don't know why variables not being passed geom_smooth added few more variables in function.

flimplot <- function(data) {      y <- data$e     x <- data$rfp_fold     <- max(dat$e)     st <- list(a=a, k=0.1)     fit <- nls(formula="e ~ * (rfp_fold / (rfp_fold + k))", dat, start=st )     k <- round(coef(fit))      ggplot(data, aes(x=rfp_fold, y=e)) +     geom_point(shape=1) +     #geom_text(aes(3,15, label = paste(expr, k, sep=""))) +     #annotate("text", x = 3, y = 15, label = paste(expr, k, sep="") ) +     stat_smooth( geom = "smooth",                  method=nls,   # add non linear regression fit                  formula="y ~ * (x / (x + k))",    # forumla fit                  start=st,  # set parameters                  #se = false,         # no shaded ci                  fullrange=true) +   # extend regression line     scale_y_continuous(limits = c(0, 20)) +     theme(plot.background = element_blank(),           panel.grid.major = element_blank(),           panel.grid.minor = element_blank(),           panel.border = element_blank(),            panel.background = element_blank(),            axis.line = element_line(color = 'black'),           text = element_text(size=12),           #axis.title.x = element_blank(),           #axis.title.y = element_blank(),           legend.justification=c(1,0)) +     ylab("fret e%") +     xlab("acceptor intensity")    }