Release notes for HOL4, Kananaskis-10

(Released: 10 November 2014)

We are pleased to announce the Kananaskis-10 release of HOL 4.

Contents

• New features
• Bugs fixed
• New theories
• New tools
• Examples
• Incompatibilities

New features:

• Our TUTORIAL and LOGIC manuals are now available in Italian translations. Work on the DESCRIPTION manual is also far advanced. Many, many thanks to Domenico Masini for doing this work.

• The abbreviation tactics (Q.ABBREV_TAC and others) now handle abstractions as abbreviations better. In particular, if one sets up an abstraction as an abbreviation (e.g., Q.ABBREV_TAC f = (λn. 2 * n + 10)``), then the simplifier will find and replace instances not just of the abstraction itself (the old behaviour), but also instances of applications of the abstraction to arguments. For example, given the abbreviation for f above, the simplifier would turn a goal such as `2 * (z + 1) + 10 < 100` into `f (z + 1) < 100`.

• The MAX_SET function in pred_setTheory is now defined (to have value 0) on the empty set.

• There is an alternative syntax for specifying datatypes. Instead of the Hol_datatype entry-point, one can also use Datatype, which takes a slightly different syntax, inspired by Haskell. This does away with the use of the (somewhat confusing) of and => tokens.

  For example, one would define a simple type of binary tree with

     Datatype`tree = Lf num | Node tree tree`
  

  If the arguments to a constructor are not just simple types (expressible as single tokens), then they need to be enclosed in parentheses. For example:

     Datatype`mytype = Constr mytype ('a -> bool) | BaseCase`
  

  The Hol_datatype entry-point can continue to be used. However, the LaTeX output of EmitTeX uses the new format, and the various DATATYPE constructors used in the EmitML module take quotations in the new format, rather than the old.

• The arithmetic decision procedure for natural numbers will now prove slightly more goals by doing case-splits on boolean sub-terms that are not in the Presburger subset. This means that goals such as

     0 < y ⇒ x < x + (if P then y else y + 1)
  

  are now provable.

• The Vim mode for HOL now supports multiple simultaneous sessions. See its README for details.

• Many of the standard libraries now provide an add_X_compset : compset -> unit (e.g., add_pred_set_compset) to ease building of custom call-by-name evaluation conversions that don't, like EVAL, include everything in the_compset().

• Holmake has a new function, wildcard which allows expansion of “glob” patterns (e.g., *Script.sml) into lists of matching filenames.

• The standard pretty-printer now annotates constants with their types as well as variables. (Note that these annotations are typically only visible by using mouse-over tooltips in the emacs mode.) The annotation also includes the constant’s real name, in the form thy$name, making overloads easier to tell apart.

  For example, this means that it is possible to have integers, reals and numbers all in scope, to write something like MAP (+), and to then see what constants are involved by using the mouse. (See Github issue #39.)

• Unicode is handled slightly better on Windows systems. By default, the pretty-printer avoids printing with Unicode characters there, but can still parse Unicode input successfully. This is important because many of the examples distributed with HOL use Unicode characters in their scripts (nothing in src/ does). This behaviour can be adjusted by toggling the PP.avoid_unicode trace. On Windows this trace is initialised to true; elsewhere it is initialised to false.

Bugs fixed:

• Holmake was unnecessarily quiet when it compiled certain SML files.
• The “munging” code for turning HOL into LaTeX now does a better job of rendering data type definition theorems. (This change is independent of the new underlying syntax described earlier.)
• Pretty-printers added to the system with add_user_printer weren’t having terms-to-be-printed tested against the supplied patterns (except by the gross approximation provided by the built-in term-net structure). Thanks to Ramana Kumar for the bug report.
• Character literals weren’t pretty-printing to LaTeX. We also improved the handling of string literals. Thanks to Ramana Kumar for the bug reports.
• Piotr Trojanek found and fixed many documentation bugs in our various manuals.
• The remove_rules_for_term and temp_remove_rules_for_term functions tended to remove rules for binders as well as the desired rules.

New theories:

• A theory of “list ranges” (listRangeTheory). A range is a term written [ lo ..< hi ], meaning the list consisting of the (natural) numbers from lo up to, but not including, hi. The theory comes with some basic and obvious theorems, such as

     MEM i [lo ..< hi] ⇔ lo ≤ i ∧ i < hi
  

  and

     LENGTH [lo ..< hi] = hi - lo
  

• A new development in src/floating-point, which is a reworking of the theories in src/float. Key differences are listed below.

  1. The data representation:

     • The old ieeeTheory uses a pair :num # num to represent the exponent and fraction widths and a triple :num # num # num to represent sign, exponent and fraction values.

     • The new binary_ieeeTheory makes use of HOL records and bit-vectors. The floating-point type :(α, β) float has values of the form

         <| Sign : word1; Exponent : β word; Significand : α word |>
       

       The fraction and exponent widths are now constrained by the type, which facilitates type-checking and avoids having to pass size arguments to operations.

  2. The new development now supports standard bit-vector encoding schemes. The theory machine_ieeeTheory defines floating-point operations over 16-bit, 32-bit and 64-bit values. For example, the 16-bit floating point operations are defined by mapping to and from the type :(10, 5) float, which is given the type abbreviation :half. Theories for other sizes can be built using machine_ieeeLib.mk_fp_encoding.
  3. There is now syntax support via the structures binary_ieeeSyntax and machine_ieeeSyntax.
  4. Ground term evaluation is now supported for most operations. This can be enabled by loading binary_ieeeLib.
  5. The full development does not build under Moscow ML 2.01, as it makes use of the IEEEReal and PackRealBig basis structures.

• A theory of “simple Patricia trees” (sptreeTheory). This theory implements a type α sptree, which is a finite map from natural numbers to values of type α. (This type is not really a Patricia tree at all; for those, see the other theories in src/patricia.) Values of type α sptree feature efficient lookup, insertion, deletion and union (efficient when evaluated with EVAL or simplified). Though there is a efficient (linear-time) fold operation, it does not iterate over the key-value pairs in key-order.

New tools:

• New libraries enumLib and fmapalLib provide representations in pred_set and finite map types of enumerated constant sets and maps as minimum-depth binary search trees. A suitable total order on the set elements (map arguments) must be supplied, with a conversion for evaluating it; assistance with this is provided. The primary objective has been an IN_CONV, and a similar FAPPLY_CONV, operating with a logarithmic number of comparisons, but additional operations such as UNION_CONV, INTER_CONV, and FUPDATE_CONV are included and have reasonable asymptotic running times. A conversion TC_CONV implements Warshall’s algorithm for transitive closure of a binary relation (treated as a set-valued finite map).

Examples:

• The miniml example has been removed. This work has evolved into the CakeML project. That project’s git repository contains all of the material that was once in the HOL distribution, and, given its continuing evolution, much more besides.

Incompatibilities:

• In relationTheory, the theorems TC_CASES1 and TC_CASES2 have been renamed to TC_CASES1_E and TC_CASES2_E respectively, where the _E suffix indicates that these are elimination rules. In other words, these theorems are of the form TC R x y ⇒ .... This has been done so that new equivalences can be introduced under the old names. For example, TC_CASES1 now states

     TC R x z ⇔ R x z ∨ ∃y. R x y ∧ TC R y z
  

  This change makes the naming consistent with similar theorems RTC_CASES1 and RTC_CASES2 about the reflexive and transitive closure.

• A theorem stating

     ⊢ ¬(0 < n) ⇔ (n = 0)
  

  (for n a natural number) has been added to the automatic rewrites used by SRW_TAC and srw_ss().

• Some new automatic rewrites from pred_setTheory:

  • ⊢ DISJOINT (x INSERT s) t ⇔ DISJOINT s t ∧ x ∉ t (and the version of this with DISJOINT s (x INSERT t) as the l.h.s.)
  • ⊢ ∀f s. INJ f ∅ s
  • ⊢ ∀f s. INJ f s ∅ ⇔ (s = ∅)

• The add_binder and temp_add_binder entry-points in Parse have been removed. They are subsumed by set_fixity <name> Binder and temp_set_fixity <name> Binder respectively. In addition, add_binder was broken, creating an unloadable theory on export.

• There is a new automatic rewrite from oneTheory:

     ⊢ ∀v:one. v = ()
  

  stating that every value in the type one (analogue of SML’s unit type) is equal to the designated value ().

• Constants that print to the TeX backend as symbolic identifiers (e.g., non-alphanumeric tokens like +, **) are now annotated there with the \HOLSymConst command rather than \HOLConst. The default behaviour of \HOLSymConst (defined in holtexbasic.sty) is to do nothing.

• If

• Holmake is called in a directory with a Holmakefile, and

• that Holmakefile has at least one explicit target, and

• Holmake is called with no command-line targets,

then: Holmake will attempt to build only the first target in that Holmakefile. We believe that this will cause problems in only a relatively small number of scenarios. The advantage of this change is that it makes Holmake easier to control from a Holmakefile. It also makes Holmake’s behaviour rather more like that of normal make.

One scenario, among others, where this change may cause problems is where Poly/ML users have set up a rule to create a HOL heap. The fix is to prepend something like the following to your Holmakefile:

   THYFILES = $(patsubst %Script.sml,%Theory.uo,$(wildcard *.sml))
   TARGETS = $(patsubst %.sml,%.uo,$(THYFILES))

   all: $(TARGETS) ...
   .PHONY: all

so that all becomes the first target of the Holmakefile. Any previous targets, such as HOL heaps, should be inserted where the ... occurs above.

Note that Holmakefiles that only include variable declarations such as OPTIONS = ..., INCLUDES = ..., and HOLHEAP = ... don’t have any targets at all, so that Holmake’s behaviour in such files’ directories will not change.

HOL4, Kananaskis-10