Convert variable into function

Question

Sorry if this is a duplicate, but I have a variable called H. H is some complicated function of s.

Now I want to make this variable H into a formal function f[s]. I've tried just doing

f[s_] := H

But that doesn't seem to work.

H was initially a value in a InputField and the type on that InputField was an Expression.

Any ideas on how I can turn this into a proper Mathematica function?

Answer 1

Couple of ways, e.g.:

ClearAll[h, f]

h = 2 s + 3 s^2 + Sin[s];
f[sarg_] := h /. (s -> sarg)
f[2]

(* just define directly *)
ClearAll[h, f]
f[s_] := 2 s + 3 s^2 + Sin[s]
f[2]

(* 
16 + Sin[2]
16 + Sin[2]
*)