eval(parse(text="f")) on shinypass.io - eval

Question

I want to write an app that lets the user enter a function using textInput, and then does something with the function. Here is a toy example:
shinyUI(fluidPage(
titlePanel("Test"),
sidebarLayout(
sidebarPanel(
textInput("fun","function:",value="x")
),
mainPanel(
uiOutput("text")
)
)
shinyServer(function(input, output) {
findMax <- reactive({
f <- function(x) eval(parse(text = input$fun), envir = list(x))
x < seq(0,1,length=100)
max(f(x))
})
output$text <- renderText( {
findMax()
})
})
))
and this works just fine when run on my computer locally. But when i submit it to shinyapps.io i get the error: object x not found. It seems there is a problem with the envir argument of eval, but i have not been able to find out what it is.
There is of course a lot of discussion on the eval(parse()) construct in general, so if anyone has a suggestion on how to do this (have the ability to type in an expression in a box and get it turned into a function) differently i would also be grateful.
Wolfgang

Answer 1

After trying a number of things i finally got this one to work:
instead of
f <- function(x) eval(parse(text = input$fun), envir = list(x))
use
eval(parse(text = paste("f <- function(x)",input$fun,sep="")))
i have no idea why both work on my computer locally but only the second works on shinyapps.io . Also, i would still be interested if anyone has a different way to do this.
Wolfgang