[m-rev.] for review: print formatted dates and durations with io.print

[Julien Fischer]

Print formatted dates and durations with io.print.

Change the io.print family of predicates to print out the formatted version of
dates and durations rather than their underlying representation.

library/io.m:
library/stream.string_writer.m:
 	As above.

 	Avoid a change of tense in the middle of the descriptive comment
 	for {io,stream.string_writer}.print.

tests/hard_coded/Mmakefile:
tests/hard_coded/print_date.{m,exp}:
 	Add a test for the above.

Julien.

diff --git a/library/io.m b/library/io.m
index 498a532..238d36b 100644
--- a/library/io.m
+++ b/library/io.m
@@ -388,8 +388,12 @@
      % If the argument is just a single string or character, it will be printed
      % out exactly as is (unquoted).  If the argument is of type integer (i.e.
      % an arbitrary precision integer), then its decimal representation will be
-    % printed.  If the argument is of type univ, then it will print out the
-    % value stored in the univ, but not the type.
+    % printed.  If the argument is of type univ, then the value stored in the
+    % the univ will be printed out, but not the type.  If the argument is of
+    % type date_time, it will be printed out in the same form as the string
+    % returned by the function date_to_string/1.  If the argument is of type
+    % duration, it will be printed out in the same form as the string
+    % returned by the function duration_to_string/1.
      %
      % print/5 is the same as print/4 except that it allows the caller to
      % specify how non-canonical types should be handled. print/3 and
diff --git a/library/stream.string_writer.m b/library/stream.string_writer.m
index 88e1be2..88c439d 100644
--- a/library/stream.string_writer.m
+++ b/library/stream.string_writer.m
@@ -51,8 +51,12 @@
      % If the argument is just a single string or character, it will be printed
      % out exactly as is (unquoted).  If the argument is of type integer (i.e.
      % an arbitrary precision integer), then its decimal representation will be
-    % printed.  If the argument is of type univ, then it will print out the
-    % value stored in the univ, but not the type.
+    % printed.  If the argument is of type univ, then the value stored in the
+    % the univ will be printed out, but not the type.  If the argument is of
+    % type date_time, it will be printed out in the same form as the string
+    % returned by the function date_to_string/1.  If the argument is of type
+    % duration, it will be printed out in the same form as the string
+    % returned by the function duration_to_string/1.
      %
      % print/5 is the same as print/4 except that it allows the caller to
      % specify how non-canonical types should be handled.  print/4 implicitly
@@ -178,6 +182,7 @@

  :- import_module array.
  :- import_module bitmap.
+:- import_module calendar.
  :- import_module int.
  :- import_module integer.
  :- import_module require.
@@ -264,6 +269,10 @@ print(Stream, NonCanon, Term, !State) :-
          write_univ(Stream, OrigUniv, !State)
      ; dynamic_cast(Term, BigInt) ->
          put(Stream, integer.to_string(BigInt), !State)
+    ; dynamic_cast(Term, DateTime) ->
+        put(Stream, date_to_string(DateTime), !State)
+    ; dynamic_cast(Term, Duration) ->
+        put(Stream, duration_to_string(Duration), !State)
      ;
          print_quoted(Stream, NonCanon, Term, !State)
      ).
diff --git a/tests/hard_coded/Mmakefile b/tests/hard_coded/Mmakefile
index a99bc57..6dc9480 100644
--- a/tests/hard_coded/Mmakefile
+++ b/tests/hard_coded/Mmakefile
@@ -232,6 +232,7 @@ ORDINARY_PROGS=	\
  	pretty_printing \
  	prince_frameopt \
  	print_bigint \
+	print_date \
  	print_stream \
  	profdeep_seg_fault \
  	promise_equiv_with_svars \
diff --git a/tests/hard_coded/print_date.exp b/tests/hard_coded/print_date.exp
new file mode 100644
index 0000000..d831d20
--- /dev/null
+++ b/tests/hard_coded/print_date.exp
@@ -0,0 +1,2 @@
+2014-12-19 16:05:00
+P5DT7H55M
diff --git a/tests/hard_coded/print_date.m b/tests/hard_coded/print_date.m
new file mode 100644
index 0000000..7e71d32
--- /dev/null
+++ b/tests/hard_coded/print_date.m
@@ -0,0 +1,20 @@
+% vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
+
+% Test io.print with dates and durations.
+
+:- module print_date.
+:- interface.
+
+:- import_module io.
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+
+:- import_module calendar.
+
+main(!IO) :-
+    Date1 = det_init_date(2014, december, 19, 16, 5, 0, 0),
+    Date2 = det_init_date(2014, december, 25, 0, 0, 0, 0),
+    io.print_line(Date1, !IO),
+    Duration = duration(Date1, Date2),
+    io.print_line(Duration, !IO).