The builtin expr
function in TI-BASIC can be used to turn a string into an expression. Here's how to implement your function this way:
myfunction(f,xl,xu)
Func
Local a,b,x
xl→x
expr(f)→a
xu→x
expr(f)→b
Return [a,b]
EndFunc
The call to your function will be myfunction("3/x",1,2)
. Be sure to enclose the definition of f
in double quotes so it is treated as a string.