Using substitute in nested function calls

Dear List members,

I really, like the feature that one can call R functions with 
mathematical expressions, e.g.

curve(x^2, 0, 1)


I wonder, how I can construct in a simple way a function like

mycurve = function (expr) {...}

such that that a call

mycurve(x^2)

has the same effect as the call

curve(x^2, -100,100)

Below is some code that works, but it seems much to complicated: it 
first substitutes and deparses the expression, creates a string with the 
new function call and then parses and evaluates the string again. Does 
anybody know a simpler, more elegant solution?

mycurve = function(expr) {
   # The following attempt does not work
   # curve(substitute(expr),-100,100)

   # Transform original expression to a string
   org.expr = deparse(substitute(expr))
   # Construct a string, parse it and evaluates it
   eval(parse(text=paste("curve(",org.expr,",-100,100)",sep="")))
}
mycurve(x^2)

Best regards,
Sebastian

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