doc-src/Pure/theory-extensions

fixed spelling

The new Internal Interface for Theory Extension
===============================================

MMW 06-Jun-1994


In former versions of Isabelle, the interface for theory extension was
provided by extend_theory. This had many deficiencies and has been removed in
Isabelle94/2.

Instead of one monolithic function, there is now a host of small functions of
the form:

  add_XXX: ... -> theory -> theory

These provide an extension mechanism which is:

  - incremental (but non-destructive):

    An extend operation may now involve many functions of the add_XXX kind.
    These act in a purely functional manner.

  - nameless:

    One no longer needs to invent new theory names for intermediate theories.
    There's now a notion of _draft_theories_ that behave like ordinary ones
    in many cases (main exceptions: extensions of drafts are not related (wrt
    subthy); merges of drafts with unrelated theories are impossible). A
    draft is "closed" by add_thyname.

  - extendable:

    Package writers simply have to provide add_XXX like functions, which are
    built using a basic set provided by Pure Isabelle.


Here follows a sample interactive session using the new functions:

  > add_consts
  # [("nand", "[o, o] => o", NoSyn), ("#", "[o, o] => o", Infixl 30)]
  # FOL.thy;
  Building new grammar...
  val it = {Pure, IFOL, FOL, #} : theory   
  > add_axioms
  # [("nand_def", "nand(P, Q) == ~(P & Q)"), ("xor_def", "P # Q == P & ~Q | ~P & Q")]
  # it;
  val it = {Pure, IFOL, FOL, #} : theory   
  > add_thyname "Gate" it;
  val it = {Pure, IFOL, FOL, Gate} : theory   

Note that theories and theorems with a "#" draft stamp are not supposed to
persist. Typically, there is a final add_thyname somewhere with the "real"
theory name as supplied by the user.


Appendix A: Basic theory extension functions
--------------------------------------------

   val add_classes: (class list * class * class list) list -> theory -> theory
   val add_defsort: sort -> theory -> theory
   val add_types: (string * int * mixfix) list -> theory -> theory
   val add_tyabbrs: (string * string list * string * mixfix) list
     -> theory -> theory
   val add_tyabbrs_i: (string * string list * typ * mixfix) list
     -> theory -> theory
   val add_arities: (string * sort list * sort) list -> theory -> theory
   val add_consts: (string * string * mixfix) list -> theory -> theory
   val add_consts_i: (string * typ * mixfix) list -> theory -> theory
   val add_syntax: (string * string * mixfix) list -> theory -> theory
   val add_syntax_i: (string * typ * mixfix) list -> theory -> theory
   val add_trfuns:
     (string * (ast list -> ast)) list *
     (string * (term list -> term)) list *
     (string * (term list -> term)) list *
     (string * (ast list -> ast)) list -> theory -> theory
   val add_trrules: xrule list -> theory -> theory
   val add_axioms: (string * string) list -> theory -> theory
   val add_axioms_i: (string * term) list -> theory -> theory
   val add_thyname: string -> theory -> theory


Appendix B: The |> operator
---------------------------

Isabelle now provides an ML infix operator for reverse function application:

  infix |>;
  fun (x |> f) = f x;

Using this, theory extension really becomes a pleasure, e.g.:

  FOL.thy 
  |> add_consts
      [("nand", "[o, o] => o", NoSyn),
       ("#", "[o, o] => o", Infixl 30)]
  |> add_axioms
      [("nand_def", "nand(P, Q) == ~(P & Q)"),
       ("xor_def", "P # Q == P & ~Q | ~P & Q")]
  |> add_thyname "Gate";

For a real-world example simply reset delete_tmpfiles, use_thy your favourite
theory definition file and inspect the generated .XXX.thy.ML file.

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