Computers are functional mappings from inputs to outputs, sure.
Analog fire computers are continuous mappings from a continuum, a line segment (curved about a cam), to another continuum, a dial perhaps.
Symbolic operations, mapping from patterns of 0s and 1s (say) to other patterns are discrete, countable mappings.
With a real valued electrical current, discrete symbols are forced by threshold levels.
> Symbolic operations, mapping from patterns of 0s and 1s (say) to other patterns are discrete, countable mappings.
What definition of "symbolic" are you using that draws a distinction between these two cases? If it means merely something that symbolises something else (as I would usually use it), then both a position on a line segment and a pattern of voltage levels qualify. If you mean it in the narrow sense of a textual mark, that pattern of voltage levels is just as much not a "symbol" as the position on the line segment.