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In 4GL, when a parameter of a function call is set as the the returned value of a DYNAMIC-FUNCTION call, as in:

function fi returns int(i as int):
   return i.
end.
function fch returns char(ch as char):
   return ch.
end.

message fi(dynamic-function("fch", "0")). /* this shows number 0*/
message fi(dynamic-function("fch", "a")). /* this shows number parsing error and the ? char */

4GL performs an "auto-cast" from the real value's type to the expected parameter's type. The full rules are not fully-discovered yet, but at least for the above case, a string containing a valid number will be converted to its numeric representation.
The same applies for assignments, as in:

def var i as int.
i = fi(dynamic-function("fch", "0")). /* i gets set to 0*/
i = fi(dynamic-function("fch", "a")). /* this shows number parsing error and i gets set to unknown*/

This suggests that the implementation of this kind of parsing needs to be done at the assign method for each P2J implementation of the 4GL types. These assign methods in turn would get invoked from the i.e. new integer(BaseDataType) c'tor too, to allow proper parsing.