user> (eval (read-string "(+ 1 2)"))
3
You probably shouldn't ever need to do this. Macros and fns make this kind of thing unnecessary 99% of the time. This is quite brittle, and can be unsafe if these strings are coming from user input, and so on.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…