But it turns out that you actually have a cell array of character vectors, not a single character vector like you showed us. How do you expect to convert a cell array of character vectors to one function? Answer: you need to actually convert that cell array of character vectors into one character vector, just like you showed in your question.
"is there any other option?"
To do what? Convert a string to a function? No, not really. To convert your array A to a function? Quite possibly.