1signature PmatchHeuristics =
2sig
3
4   type term = Term.term
5   type thm = Thm.thm
6   type thry = {Thy : string, Tyop : string} ->
7               {case_const : term, constructors : term list} option
8   type pmatch_heuristic = {skip_rows : bool, (* skip splitting for redundant rows? *)
9                            collapse_cases : bool, (* collapse cases that lead to the same result ? *)
10                            (* given a list of rows of patterns, which column to split on? *)
11                            col_fun : thry -> term list list -> int }
12
13   (* some predefined heuristics *)
14   val pheu_classic : pmatch_heuristic (* HOL 4's old heuristic *)
15   val pheu_first_row : pmatch_heuristic
16   val pheu_constr_prefix : pmatch_heuristic
17   val pheu_qba : pmatch_heuristic  (* the recommended one *)
18   val pheu_cqba : pmatch_heuristic
19   val pheu_first_col : pmatch_heuristic
20   val pheu_last_col : pmatch_heuristic
21
22   (* A manual heuristic. For each decision, it prints the columns and
23      takes the column-number from the provided list of explicit
24      choices. If the list is too short, the first column is
25      chosen. One should run this heuristic first with an empty list
26      as argument. Then look at the choices and add 0s for all the
27      initial choices you liked to be 0 an then a different choice you
28      prefer. Rerun again (because the following choices will change)
29      and iterate. This provided very fine control, but is tedious. *)
30   val pheu_manual : int list -> pmatch_heuristic
31
32   (* A heuristic based on column ranks. Given a pattern match matrix like
33
34      p_11 ... p_1n
35      ...
36      p_m1 --- p_mn
37
38      and a list of ranking functions prheuL = [r_1, ... r_j]. The
39      heuristic pheu_rank applies all ranking functions to all columns.
40      Let's denote the result of "r_i current_thyr [p_k1, ... pkm]" with
41      c_ik. It then picks column i such that [c_1i, ... c_ji] is maximal
42      accroding to the lexicographic ordering of integers.
43   *)
44   val pheu_rank : (thry -> term list -> int) list -> pmatch_heuristic
45
46   (* some ranking functions *)
47   val prheu_first_row : thry -> term list -> int
48   val prheu_constr_prefix : thry -> term list -> int
49   val prheu_small_branching_factor : thry -> term list -> int
50   val prheu_arity : thry -> term list -> int
51
52   (* A comparison for the results of heuristic application
53      (list of pattern lists, resulting decision tree) *)
54   type pmatch_heuristic_res_compare = (term list list * term) Lib.cmp
55   val pmatch_heuristic_cases_cmp : pmatch_heuristic_res_compare (* few cases are good *)
56   val pmatch_heuristic_size_cmp : pmatch_heuristic_res_compare (* small terms are good *)
57
58   (* Using such comparisons, we can supply multiple heuristics and choose the best results.
59      For technical reasons, this function might be stateful and therefore get's unit arguments.
60
61      The usage of a heu_fun by the Pmatch library is as follows. Heu_fun initialises the functions and returns a
62      compare function and a function heu_fun' which provides heuristics. As long as
63      heu_fun' () provides fresh heuristics these are tried. Then the best result of all these
64      heuristics according to the compare function is choosen. *)
65   type pmatch_heuristic_fun = unit -> pmatch_heuristic_res_compare * (unit -> pmatch_heuristic option)
66
67   val default_heuristic_fun : pmatch_heuristic_fun
68   val classic_heuristic_fun : pmatch_heuristic_fun
69
70   (* An exhaustive heuristic_fun. It tries all possibilities and very quickly blows up!
71      Only usable for very small examples! *)
72   val exhaustive_heuristic_fun : pmatch_heuristic_res_compare -> pmatch_heuristic_fun
73
74
75   (* custom pmatch_heuristic_fun can be easiest constructed by an explicit list of heuristics and
76      a compare function *)
77   val pmatch_heuristic_list : pmatch_heuristic_res_compare -> pmatch_heuristic list -> pmatch_heuristic_fun
78
79   (* A list of useful heuristics to be used with pmatch_heuristic_list *)
80   val default_heuristic_list : pmatch_heuristic list
81
82
83   (* The pmatch_heuristic_fun to be used by default and various functions to set it *)
84   val pmatch_heuristic : pmatch_heuristic_fun ref
85
86   val set_heuristic : pmatch_heuristic -> unit
87   val set_heuristic_fun : pmatch_heuristic_fun -> unit
88   val set_heuristic_list_size : pmatch_heuristic list -> unit
89   val set_heuristic_list_cases : pmatch_heuristic list -> unit
90   val set_default_heuristic : unit -> unit
91   val set_classic_heuristic : unit -> unit
92
93   val with_classic_heuristic : ('a -> 'b) -> ('a -> 'b)
94   val with_heuristic : pmatch_heuristic -> ('a -> 'b) -> ('a -> 'b)
95   val with_manual_heuristic : int list -> ('a -> 'b) -> ('a -> 'b)
96   val is_classic : unit -> bool
97end
98