[R] help with as.function

[solares@unsl.edu.ar]

HI, sorry but i don't understand how to make a function with as.function()

formula<-"2+3*x"
 formu<-as.symbol(formula)
> formu
2+3*x
 formul<-as.function(alist(x=,formu))
curve(formul,1,5,col="blue")
Error in xy.coords(x, y, xlabel, ylabel, log) :
        x and y lengths differ
> typeof(formul)
[1] "closure"

and not plot the curve function, Why? Thanks Ruben