如何使用公式作爲曲線中的字符矢量（）

Question

我有一個公式作爲字符矢量，並且想在curve中使用它。

curve(-8*cos(2*x), 0, 10) #works as expected 
formula <- "-8*cos(2*x)" 

# nothing works 

curve(formula, 0, 10) 
# Error in formula.default(x) : invalid formula 

curve(eval(formula), 0, 10) 
# Error in curve(eval(formula), 0, 10) : 
# 'expr' must be a function, or a call or an expression containing 'x' 

curve(as.expression(formula), 0, 10) 
# Error in curve(as.expression(formula), 0, 10) : 
# 'expr' must be a function, or a call or an expression containing 'x' 

curve(eval(as.expression(formula)), 0, 10) 
# Error in curve(eval(as.expression(formula)), 0, 10) : 
# 'expr' must be a function, or a call or an expression containing 'x' 

curve(parse(text = formula), 0, 10) 
# Error in curve(parse(text = formula), 0, 10) : 
# 'expr' must be a function, or a call or an expression containing 'x' 

curve(eval(parse(text = formula)), 0, 10) 
# Error in curve(eval(parse(text = formula)), 0, 10) : 
# 'expr' must be a function, or a call or an expression containing 'x' 

我的問題
我怎樣才能使這項工作？

Answer 1

一種可能性是簡單地包裹在一個功能，

curve((function(x) eval(parse(text=formula)))(x), 0, 10)