pub fn convert_input(file: &mut PolydatFile, name: &str) -> Result<(), String>Expand description
Let the program’s extern name take a value of any type, converted
in front of each reader by a converter node (input_variance.md §6).
The extern is declared dyn; the compiler places one converter per
type its readers read, reports each in the compile log, and a value
the converter cannot convert fails the converter, attributed as any
node’s failure. For one input a host knows varies, without opening
every input the author left untyped. A name that is not a top-level
extern is an error: a coordinate is positioned with set_inputs
and never varies in type.