adjoin_to_theory : thy_addon -> unit
STRUCTURE
Theory
SYNOPSIS
Include arbitrary ML in exported theory.
DESCRIPTION
It often happens that algorithms and flag settings accompany a logical theory (call it thy). One would want to simply load the thyTheory module and have the appropriate proof support, etc. loaded automatically as well.

There are several ways to support this. One simple way would be to define another ML structure, thySupport say, that depended on thyTheory. The algorithms, etc, could be placed in thySupport and the interested user would know that by loading thySupport, its contents, and those of thyTheory, would become available. This approach, and extensions of it are accomodated already in the notion of a HOL library.

However, it is sometimes more appropriate to actually include the support code directly in thyTheory. The function adjoin_to_theory performs this operation.

A call adjoin_to_theory {sig_ps, struct_ps} adds a signature prettyprinter sig_ps and a structure prettyprinter struct_ps to an internal queue of prettyprinters. When export_theory () is eventually called two things happen: (a) the signature file thyTheory.sig is written, and (b) the structure file thyTheory.sml is written. When thyTheory.sig is written, each signature prettyprinter in the queue is called, in the order that they were added to the queue. This printing activity happens after the rest of the signature (coming from the declarations in the theory) has been written. Similarly, when thyTheory.sml is written, the structure prettyprinters are invoked in queue order, after the bindings of the theory have been written.

If sig_ps is NONE, then no signature additions are made. Likewise, if struct_ps is NONE, then no structure additions are made. (This latter possibility doesn’t seem to be useful.)

FAILURE
It is up to the writer of a prettyprinter to ensure that it generates valid ML. If a prettyprinter added by a call to adjoin_to_theory fails, thyTheory.sig or thyTheory.sml could be malformed, and therefore not properly exported, or compiled.
EXAMPLE
The following excerpt from the script for the theory of pairs is a fairly typical use of adjoin_to_theory. It adds the declaration of an ML variable pair_rws to the structure pairTheory. 
   val _ = adjoin_to_theory
   {sig_ps =
      SOME(fn ppstrm => PP.add_string ppstrm "val pair_rws:thm list"),
    struct_ps =
      SOME(fn ppstrm => PP.add_string ppstrm
                             "val pair_rws = [PAIR, FST, SND];")
   }

COMMENTS
The PP structure is documented in the MoscowML library documentation.
SEEALSO
thy_addon, export_rewrites
HOL  Trindemossen-1