(* Title: Pure/Syntax/ast.ML
Author: Markus Wenzel, TU Muenchen
Abstract syntax trees, translation rules, matching and normalization of asts.
*)
signature AST =
sig
datatype ast =
Constant of string |
Variable of string |
Appl of ast list
val mk_appl: ast -> ast list -> ast
exception AST of string * ast list
val pretty_ast: ast -> Pretty.T
val pretty_rule: ast * ast -> Pretty.T
val strip_positions: ast -> ast
val head_of_rule: ast * ast -> string
val rule_error: ast * ast -> string option
val fold_ast: string -> ast list -> ast
val fold_ast_p: string -> ast list * ast -> ast
val unfold_ast: string -> ast -> ast list
val unfold_ast_p: string -> ast -> ast list * ast
val trace: bool Config.T
val stats: bool Config.T
val normalize: Proof.context -> (string -> (ast * ast) list) -> ast -> ast
end;
structure Ast: AST =
struct
(** abstract syntax trees **)
(*asts come in two flavours:
- ordinary asts representing terms and typs: Variables are (often) treated
like Constants;
- patterns used as lhs and rhs in rules: Variables are placeholders for
proper asts*)
datatype ast =
Constant of string | (*"not", "_abs", "fun"*)
Variable of string | (*x, ?x, 'a, ?'a*)
Appl of ast list; (*(f x y z), ("fun" 'a 'b), ("_abs" x t)*)
(*the list of subasts of an Appl node has to contain at least 2 elements, i.e.
there are no empty asts or nullary applications; use mk_appl for convenience*)
fun mk_appl f [] = f
| mk_appl f args = Appl (f :: args);
(*exception for system errors involving asts*)
exception AST of string * ast list;
(** print asts in a LISP-like style **)
fun pretty_ast (Constant a) = Pretty.quote (Pretty.str a)
| pretty_ast (Variable x) =
(case Term_Position.decode x of
SOME pos => Term_Position.pretty pos
| NONE => Pretty.str x)
| pretty_ast (Appl asts) = Pretty.enclose "(" ")" (Pretty.breaks (map pretty_ast asts));
fun pretty_rule (lhs, rhs) =
Pretty.block [pretty_ast lhs, Pretty.str " \<leadsto>", Pretty.brk 1, pretty_ast rhs];
val _ = ML_system_pp (fn _ => fn _ => Pretty.to_polyml o pretty_ast);
(* strip_positions *)
fun strip_positions (Appl ((t as Constant c) :: u :: (v as Variable x) :: asts)) =
if member (op =) Term_Position.markers c andalso is_some (Term_Position.decode x)
then mk_appl (strip_positions u) (map strip_positions asts)
else Appl (map strip_positions (t :: u :: v :: asts))
| strip_positions (Appl asts) = Appl (map strip_positions asts)
| strip_positions ast = ast;
(* head_of_ast and head_of_rule *)
fun head_of_ast (Constant a) = a
| head_of_ast (Appl (Constant a :: _)) = a
| head_of_ast _ = "";
fun head_of_rule (lhs, _) = head_of_ast lhs;
(** check translation rules **)
fun rule_error (lhs, rhs) =
let
fun add_vars (Constant _) = I
| add_vars (Variable x) = cons x
| add_vars (Appl asts) = fold add_vars asts;
val lvars = add_vars lhs [];
val rvars = add_vars rhs [];
in
if has_duplicates (op =) lvars then SOME "duplicate vars in lhs"
else if not (subset (op =) (rvars, lvars)) then SOME "rhs contains extra variables"
else NONE
end;
(** ast translation utilities **)
(* fold asts *)
fun fold_ast _ [] = raise Match
| fold_ast _ [y] = y
| fold_ast c (x :: xs) = Appl [Constant c, x, fold_ast c xs];
fun fold_ast_p c = uncurry (fold_rev (fn x => fn xs => Appl [Constant c, x, xs]));
(* unfold asts *)
fun unfold_ast c (y as Appl [Constant c', x, xs]) =
if c = c' then x :: unfold_ast c xs else [y]
| unfold_ast _ y = [y];
fun unfold_ast_p c (y as Appl [Constant c', x, xs]) =
if c = c' then apfst (cons x) (unfold_ast_p c xs)
else ([], y)
| unfold_ast_p _ y = ([], y);
(** normalization of asts **)
(* match *)
fun match ast pat =
let
exception NO_MATCH;
fun mtch (Constant a) (Constant b) env =
if a = b then env else raise NO_MATCH
| mtch (Variable a) (Constant b) env =
if a = b then env else raise NO_MATCH
| mtch ast (Variable x) env = Symtab.update (x, ast) env
| mtch (Appl asts) (Appl pats) env = mtch_lst asts pats env
| mtch _ _ _ = raise NO_MATCH
and mtch_lst (ast :: asts) (pat :: pats) env =
mtch_lst asts pats (mtch ast pat env)
| mtch_lst [] [] env = env
| mtch_lst _ _ _ = raise NO_MATCH;
val (head, args) =
(case (ast, pat) of
(Appl asts, Appl pats) =>
let val a = length asts and p = length pats in
if a > p then (Appl (take p asts), drop p asts)
else (ast, [])
end
| _ => (ast, []));
in
SOME (mtch head pat Symtab.empty, args) handle NO_MATCH => NONE
end;
(* normalize *)
val trace = Config.declare_bool ("syntax_ast_trace", \<^here>) (K false);
val stats = Config.declare_bool ("syntax_ast_stats", \<^here>) (K false);
fun message head body =
Pretty.string_of (Pretty.block [Pretty.str head, Pretty.brk 1, body]);
(*the normalizer works yoyo-like: top-down, bottom-up, top-down, ...*)
fun normalize ctxt get_rules pre_ast =
let
val trace = Config.get ctxt trace;
val stats = Config.get ctxt stats;
val passes = Unsynchronized.ref 0;
val failed_matches = Unsynchronized.ref 0;
val changes = Unsynchronized.ref 0;
fun subst _ (ast as Constant _) = ast
| subst env (Variable x) = the (Symtab.lookup env x)
| subst env (Appl asts) = Appl (map (subst env) asts);
fun try_rules ((lhs, rhs) :: pats) ast =
(case match ast lhs of
SOME (env, args) =>
(Unsynchronized.inc changes; SOME (mk_appl (subst env rhs) args))
| NONE => (Unsynchronized.inc failed_matches; try_rules pats ast))
| try_rules [] _ = NONE;
val try_headless_rules = try_rules (get_rules "");
fun try ast a =
(case try_rules (get_rules a) ast of
NONE => try_headless_rules ast
| some => some);
fun rewrite (ast as Constant a) = try ast a
| rewrite (ast as Variable a) = try ast a
| rewrite (ast as Appl (Constant a :: _)) = try ast a
| rewrite (ast as Appl (Variable a :: _)) = try ast a
| rewrite ast = try_headless_rules ast;
fun rewrote old_ast new_ast =
if trace then tracing (message "rewrote:" (pretty_rule (old_ast, new_ast)))
else ();
fun norm_root ast =
(case rewrite ast of
SOME new_ast => (rewrote ast new_ast; norm_root new_ast)
| NONE => ast);
fun norm ast =
(case norm_root ast of
Appl sub_asts =>
let
val old_changes = ! changes;
val new_ast = Appl (map norm sub_asts);
in
if old_changes = ! changes then new_ast else norm_root new_ast
end
| atomic_ast => atomic_ast);
fun normal ast =
let
val old_changes = ! changes;
val new_ast = norm ast;
in
Unsynchronized.inc passes;
if old_changes = ! changes then new_ast else normal new_ast
end;
val _ = if trace then tracing (message "pre:" (pretty_ast pre_ast)) else ();
val post_ast = normal pre_ast;
val _ =
if trace orelse stats then
tracing (message "post:" (pretty_ast post_ast) ^ "\nnormalize: " ^
string_of_int (! passes) ^ " passes, " ^
string_of_int (! changes) ^ " changes, " ^
string_of_int (! failed_matches) ^ " matches failed")
else ();
in post_ast end;
end;