Equation of Tangent

[vjc]

The working program, if needed by anyone else, is as follows:
(Credit goes to roadrunner to correct my shoddy programming)


BEGIN
LOCAL f, B;
PRINT;
INPUT ({{f,[2],40}}, "Function:", "f (X) =", "Enter the algebraic expression");
f ▶ F1;
INPUT (A, "Study of the tangent at x =?", " X =");
PRINT ("f (X) =" + F1);
PRINT ("Equation of the tangent at " + A + " :");
PRINT ("Y =" + SLOPE (F1, A) + "(X -" + A + ") +" + F1 (A));
−SLOPE (F1, A) * A + F1 (A) ▶ B;
PRINT ("that is: Y =" + SLOPE (F1, A) + IFTE(B<0,"X -","X +") + ABS(B));
END;


There is scope for improvement here but is beyond my limited programming skills.
I would love if instead of typing in the algebraic expression at the very first input, we would just type, say 1, and it would pick up the expression F1(X) from function symbolic view, and similarly pressing 2 would pick up the expression F2(X) from function symbolic view and so on. This will save the effort of retyping or copy-pasting the entire expression. Any ideas anyone??