Co-algebraic data sources.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Syntax/source.ML	Mon May 18 18:08:58 1998 +0200
@@ -0,0 +1,143 @@
+(*  Title:      Isar/source.ML
+    ID:         $Id$
+    Author:     Markus Wenzel, TU Muenchen
+
+Co-algebraic data sources.
+
+TODO:
+  - proper handling of interrupts (?);
+  - recovery from scan errors (?);
+  - make prompt part of source (?);
+*)
+
+signature SOURCE =
+sig
+  type ('a, 'b) source
+  val get: string -> ('a, 'b) source -> 'a list * ('a, 'b) source
+  val unget: 'a list * ('a, 'b) source -> ('a, 'b) source
+  val get_single: string -> ('a, 'b) source -> 'a * ('a, 'b) source
+  val exhaust: string -> ('a, 'b) source -> 'a list
+  val filter: ('a -> bool) -> ('a, 'b) source -> ('a, ('a, 'b) source) source
+  val of_list: int option -> 'a list -> ('a, 'a list) source
+  val of_string: int option -> string -> (string, string list) source
+  val of_stream: TextIO.instream -> TextIO.outstream -> (string, unit) source
+  val tty: (string, unit) source
+  val state_source: 'a -> 'b * ('b -> bool) -> ('a * 'b list -> 'c list * ('a * 'b list))
+    -> ('b, 'd) source -> ('c, 'a * ('b, 'd) source) source
+  val source: 'a * ('a -> bool) -> ('a list -> 'b list * 'a list)
+    -> ('a, 'c) source -> ('b, ('a, 'c) source) source
+  val test: ('a -> string) -> ('a, 'b) source -> unit
+end;
+
+structure Source: SOURCE =
+struct
+
+
+(** datatype source **)
+
+datatype ('a, 'b) source =
+  Source of
+   {buffer: 'a list,
+    info: 'b,
+    drain: string -> 'b -> 'a list * 'b};
+
+fun make_source buffer info drain =
+  Source {buffer = buffer, info = info, drain = drain};
+
+
+(* get / unget *)
+
+fun get prompt (Source {buffer = [], info, drain}) =
+      let val (xs, info') = drain prompt info
+      in (xs, make_source [] info' drain) end
+  | get _ (Source {buffer, info, drain}) =
+      (buffer, make_source [] info drain);
+
+fun unget (xs, Source {buffer, info, drain}) =
+  make_source (xs @ buffer) info drain;
+
+
+fun get_single prompt src =
+  (case get prompt src of
+    ([], _) => error "Input source exhausted!"
+  | (x :: xs, src') => (x, unget (xs, src')));
+
+fun exhaust prompt src =
+  (case get prompt src of
+    ([], _) => []
+  | (xs, src') => xs @ exhaust prompt src');
+
+
+(* filter *)
+
+fun drain_filter pred prompt src =
+  let
+    val (xs, src') = get prompt src;
+    val xs' = Library.filter pred xs;
+  in
+    if null xs then (xs, src')
+    else if null xs' then drain_filter pred prompt src'
+    else (xs', src')
+  end;
+
+fun filter pred src = make_source [] src (drain_filter pred);
+
+
+
+(** build sources **)
+
+(* list source *)
+
+fun drain_list _ xs = (xs, []);
+fun drain_list_limit n _ xs = (take (n, xs), drop (n, xs));
+
+fun of_list None xs = make_source [] xs drain_list
+  | of_list (Some n) xs = make_source [] xs (drain_list_limit (Int.max (n, 1)));
+
+fun of_string limit str = of_list limit (explode str);
+
+
+(* stream source *)
+
+fun drain_stream instream outstream prompt () =
+  (TextIO.output (outstream, prompt);
+    TextIO.flushOut outstream;
+    (explode (TextIO.inputLine instream), ()));
+
+fun of_stream instream outstream =
+  make_source [] () (drain_stream instream outstream);
+
+val tty = of_stream TextIO.stdIn TextIO.stdOut;
+
+
+
+(** compose sources **)
+
+(* make state-based *)
+
+fun drain_state_source stopper scan prompt state_src =
+  Scan.source prompt get unget stopper scan state_src;
+
+fun state_source init_state stopper scan src =
+  make_source [] (init_state, src) (drain_state_source stopper scan);
+
+
+(* not state-based *)
+
+fun drain_source stopper scan prompt src =
+  apsnd snd (Scan.source prompt get unget stopper (Scan.lift scan) ((), src));
+
+fun source stopper scan src =
+   make_source [] src (drain_source stopper scan);
+
+
+
+(** test source interactively **)
+
+fun test str_of src =
+  (case get ">> " src handle Interrupt => ([], src) of
+    ([], _) => writeln "Terminated."
+  | (xs, src') => (seq writeln (map str_of xs); test str_of src'));
+
+
+end;