Is it possible to call Singular from Delphi?
It depends:
Yes, Singular can be called from Delphi in the way each program can
be called (and transfer the data via files).
And no, it is (in some sense) a C++ library and can be accessed
from C++ programs, but we have no idea
how to access it from other languages: many of its routines
are inline procedures and macros.