src/Doc/Codegen/Further.thy
 author blanchet Tue Nov 07 15:16:42 2017 +0100 (23 months ago) changeset 67022 49309fe530fd parent 66453 cc19f7ca2ed6 child 67207 ad538f6c5d2f permissions -rw-r--r--
more robust parsing for THF proofs (esp. polymorphic Leo-III proofs)
     1 theory Further

     2 imports Codegen_Basics.Setup

     3 begin

     4

     5 section \<open>Further issues \label{sec:further}\<close>

     6

     7 subsection \<open>Incorporating generated code directly into the system runtime -- @{text code_reflect}\<close>

     8

     9 subsubsection \<open>Static embedding of generated code into the system runtime\<close>

    10

    11 text \<open>

    12   The @{ML_antiquotation code} antiquotation is lightweight, but the generated code

    13   is only accessible while the ML section is processed.  Sometimes this

    14   is not appropriate, especially if the generated code contains datatype

    15   declarations which are shared with other parts of the system.  In these

    16   cases, @{command_def code_reflect} can be used:

    17 \<close>

    18

    19 code_reflect %quote Sum_Type

    20   datatypes sum = Inl | Inr

    21   functions "Sum_Type.sum.projl" "Sum_Type.sum.projr"

    22

    23 text \<open>

    24   \noindent @{command code_reflect} takes a structure name and

    25   references to datatypes and functions; for these code is compiled

    26   into the named ML structure and the \emph{Eval} target is modified

    27   in a way that future code generation will reference these

    28   precompiled versions of the given datatypes and functions.  This

    29   also allows to refer to the referenced datatypes and functions from

    30   arbitrary ML code as well.

    31

    32   A typical example for @{command code_reflect} can be found in the

    33   @{theory Predicate} theory.

    34 \<close>

    35

    36

    37 subsubsection \<open>Separate compilation\<close>

    38

    39 text \<open>

    40   For technical reasons it is sometimes necessary to separate

    41   generation and compilation of code which is supposed to be used in

    42   the system runtime.  For this @{command code_reflect} with an

    43   optional \<^theory_text>\<open>file\<close> argument can be used:

    44 \<close>

    45

    46 code_reflect %quote Rat

    47   datatypes rat

    48   functions Fract

    49     "(plus :: rat \<Rightarrow> rat \<Rightarrow> rat)" "(minus :: rat \<Rightarrow> rat \<Rightarrow> rat)"

    50     "(times :: rat \<Rightarrow> rat \<Rightarrow> rat)" "(divide :: rat \<Rightarrow> rat \<Rightarrow> rat)"

    51   file "\$ISABELLE_TMP/rat.ML"

    52

    53 text \<open>

    54   \noindent This merely generates the referenced code to the given

    55   file which can be included into the system runtime later on.

    56 \<close>

    57

    58 subsection \<open>Specialities of the @{text Scala} target language \label{sec:scala}\<close>

    59

    60 text \<open>

    61   @{text Scala} deviates from languages of the ML family in a couple

    62   of aspects; those which affect code generation mainly have to do with

    63   @{text Scala}'s type system:

    64

    65   \begin{itemize}

    66

    67     \item @{text Scala} prefers tupled syntax over curried syntax.

    68

    69     \item @{text Scala} sacrifices Hindely-Milner type inference for a

    70       much more rich type system with subtyping etc.  For this reason

    71       type arguments sometimes have to be given explicitly in square

    72       brackets (mimicking System F syntax).

    73

    74     \item In contrast to @{text Haskell} where most specialities of

    75       the type system are implemented using \emph{type classes},

    76       @{text Scala} provides a sophisticated system of \emph{implicit

    77       arguments}.

    78

    79   \end{itemize}

    80

    81   \noindent Concerning currying, the @{text Scala} serializer counts

    82   arguments in code equations to determine how many arguments

    83   shall be tupled; remaining arguments and abstractions in terms

    84   rather than function definitions are always curried.

    85

    86   The second aspect affects user-defined adaptations with @{command

    87   code_printing}.  For regular terms, the @{text Scala} serializer prints

    88   all type arguments explicitly.  For user-defined term adaptations

    89   this is only possible for adaptations which take no arguments: here

    90   the type arguments are just appended.  Otherwise they are ignored;

    91   hence user-defined adaptations for polymorphic constants have to be

    92   designed very carefully to avoid ambiguity.

    93 \<close>

    94

    95

    96 subsection \<open>Modules namespace\<close>

    97

    98 text \<open>

    99   When invoking the @{command export_code} command it is possible to

   100   leave out the @{keyword "module_name"} part; then code is

   101   distributed over different modules, where the module name space

   102   roughly is induced by the Isabelle theory name space.

   103

   104   Then sometimes the awkward situation occurs that dependencies

   105   between definitions introduce cyclic dependencies between modules,

   106   which in the @{text Haskell} world leaves you to the mercy of the

   107   @{text Haskell} implementation you are using, while for @{text

   108   SML}/@{text OCaml} code generation is not possible.

   109

   110   A solution is to declare module names explicitly.  Let use assume

   111   the three cyclically dependent modules are named \emph{A}, \emph{B}

   112   and \emph{C}.  Then, by stating

   113 \<close>

   114

   115 code_identifier %quote

   116   code_module A \<rightharpoonup> (SML) ABC

   117 | code_module B \<rightharpoonup> (SML) ABC

   118 | code_module C \<rightharpoonup> (SML) ABC

   119

   120 text \<open>

   121   \noindent we explicitly map all those modules on \emph{ABC},

   122   resulting in an ad-hoc merge of this three modules at serialisation

   123   time.

   124 \<close>

   125

   126 subsection \<open>Locales and interpretation\<close>

   127

   128 text \<open>

   129   A technical issue comes to surface when generating code from

   130   specifications stemming from locale interpretation into global

   131   theories.

   132

   133   Let us assume a locale specifying a power operation on arbitrary

   134   types:

   135 \<close>

   136

   137 locale %quote power =

   138   fixes power :: "'a \<Rightarrow> 'b \<Rightarrow> 'b"

   139   assumes power_commute: "power x \<circ> power y = power y \<circ> power x"

   140 begin

   141

   142 text \<open>

   143   \noindent Inside that locale we can lift @{text power} to exponent

   144   lists by means of a specification relative to that locale:

   145 \<close>

   146

   147 primrec %quote powers :: "'a list \<Rightarrow> 'b \<Rightarrow> 'b" where

   148   "powers [] = id"

   149 | "powers (x # xs) = power x \<circ> powers xs"

   150

   151 lemma %quote powers_append:

   152   "powers (xs @ ys) = powers xs \<circ> powers ys"

   153   by (induct xs) simp_all

   154

   155 lemma %quote powers_power:

   156   "powers xs \<circ> power x = power x \<circ> powers xs"

   157   by (induct xs)

   158     (simp_all del: o_apply id_apply add: comp_assoc,

   159       simp del: o_apply add: o_assoc power_commute)

   160

   161 lemma %quote powers_rev:

   162   "powers (rev xs) = powers xs"

   163     by (induct xs) (simp_all add: powers_append powers_power)

   164

   165 end %quote

   166

   167 text \<open>

   168   After an interpretation of this locale (say, @{command_def

   169   global_interpretation} @{text "fun_power:"} @{term [source] "power (\<lambda>n (f

   170   :: 'a \<Rightarrow> 'a). f ^^ n)"}), one could naively expect to have a constant @{text

   171   "fun_power.powers :: nat list \<Rightarrow> ('a \<Rightarrow> 'a) \<Rightarrow> 'a \<Rightarrow> 'a"} for which code

   172   can be generated.  But this not the case: internally, the term

   173   @{text "fun_power.powers"} is an abbreviation for the foundational

   174   term @{term [source] "power.powers (\<lambda>n (f :: 'a \<Rightarrow> 'a). f ^^ n)"}

   175   (see @{cite "isabelle-locale"} for the details behind).

   176

   177   Fortunately, a succint solution is available: a dedicated

   178   rewrite definition:

   179 \<close>

   180

   181 global_interpretation %quote fun_power: power "(\<lambda>n (f :: 'a \<Rightarrow> 'a). f ^^ n)"

   182   defines funpows = fun_power.powers

   183   by unfold_locales

   184     (simp_all add: fun_eq_iff funpow_mult mult.commute)

   185

   186 text \<open>

   187   \noindent This amends the interpretation morphisms such that

   188   occurrences of the foundational term @{term [source] "power.powers (\<lambda>n (f :: 'a \<Rightarrow> 'a). f ^^ n)"}

   189   are folded to a newly defined constant @{const funpows}.

   190

   191   After this setup procedure, code generation can continue as usual:

   192 \<close>

   193

   194 text %quotetypewriter \<open>

   195   @{code_stmts funpows (consts) Nat.funpow funpows (Haskell)}

   196 \<close>

   197

   198

   199 subsection \<open>Parallel computation\<close>

   200

   201 text \<open>

   202   Theory @{text Parallel} in \<^dir>\<open>~~/src/HOL/Library\<close> contains

   203   operations to exploit parallelism inside the Isabelle/ML

   204   runtime engine.

   205 \<close>

   206

   207 subsection \<open>Imperative data structures\<close>

   208

   209 text \<open>

   210   If you consider imperative data structures as inevitable for a

   211   specific application, you should consider \emph{Imperative

   212   Functional Programming with Isabelle/HOL}

   213   @{cite "bulwahn-et-al:2008:imperative"}; the framework described there

   214   is available in session @{text Imperative_HOL}, together with a

   215   short primer document.

   216 \<close>

   217

   218 end