"silly" (?) Ada semantics

[mfeldman@seas.gwu.edu (Michael Feldman)]

A recent posting suggested trying the following program on my compiler:

    procedure MAIN is
        A: array(1..2, 1..3) of INTEGER;
    begin
        A := ((2,2),(3,3,3), (4,4,4,4));
    end MAIN;

Well, here are the results, in the order Irvine (HP835), Meridian (Sun-3),
Verdix (Sun-3), TeleSoft (Sun-3). In all 4 cases, the compilers flagged the
offending initialization of the array with warnings indicating that
constraint_error would be raised at execution time. What is the point
about the "silly" semantics: that the compiler should treat it as fatal?
Well, OK, maybe it should. As a teacher of compiler construction, I know
well that the question of what to treat as a fatal error is really a
matter of taste. Let's not turn this into a religious thing, OK?

   ---------- cut here ------------

    1 | procedure MAIN is
    2 |         A: array(1..2, 1..3) of INTEGER;
    3 |     begin
    4 |         A := ((2,2),(3,3,3), (4,4,4,4));
***** > "silly.ada", line 4: Exception Warning: LRM4.3.2.11 Subaggregate array bounds not the same.
***** > "silly.ada", line 4: Exception Warning: LRM4.3.2.11 Subaggregate array bounds not the same.
***** > "silly.ada", line 4: Warning: Incompatible array bounds (1..4 not compatible with 1..3).
    5 |     end MAIN;
***** > "silly.ada", line 2: Advisory Warning: Variable A never read.

5 lines compiled.
No errors detected.
4 warnings issued.

  ----------- cut here ----------

    Meridian AdaVantage v4.0  Source file: silly.ada  Page 1
    Sat Jun  2 1990 16:47:46 EDT


        1  procedure MAIN is
        2          A: array(1..2, 1..3) of INTEGER;
        3      begin
        4          A := ((2,2),(3,3,3), (4,4,4,4));
        +
    +++++W subtype check will raise constraint_error [LRM 10.6/3]
        +
        +
    +++++W value out of range will raise constraint_error [LRM 10.6/3]
        +
        +
    +++++W subtype check will raise constraint_error [LRM 10.6/3]
        +
        +
    +++++W value out of range will raise constraint_error [LRM 10.6/3]
        +
        +
    +++++W value out of range will raise constraint_error [LRM 10.6/3]
        +
        5      end MAIN;
  
  ----------- cut here ----------


Verdix Ada Compiler, Copyright 1984, 1985, 1986, 1987, 1988, 1989
Version 5.7 - Sun UNIX
Fri Apr 21 08:49:57 PDT 1989 (d)

File: /usr.MC68020/sparko/1/faculty/mfeldman/verdix/silly.ada
	compiled Sat Jun  2 16:51:16 1990
	by user mfeldman

	floating point processor MC68881

unit:	subprogram body main
	NO Ada ERRORS		UNIT ENTERED

3 statements	5 lines

*********************************  silly.ada  *********************************

   1:procedure MAIN is
   2:        A: array(1..2, 1..3) of INTEGER;
   3:    begin
   4:        A := ((2,2),(3,3,3), (4,4,4,4));
A -------------^
B ----------------^
C -----------------^
D --------------------------------^
A:warning: RM 5.2.1(2): arrays have different sizes: will raise CONSTRAINT_ERROR
B:warning: RM 3.6.1(16) and 5.2.1(2): wrong number of elements
B:warning: bounds check will raise CONSTRAINT_ERROR at runtime
B:warning: bounds check will raise CONSTRAINT_ERROR at runtime
B:warning: RM 3.6.1: bounds check will raise CONSTRAINT_ERROR at runtime
B:warning: RM 3.6.1: bounds check will raise CONSTRAINT_ERROR at runtime
C:warning: RM 3.6.1(16) and 5.2.1(2): wrong number of elements
D:warning: RM 3.6.1(16) and 5.2.1(2): wrong number of elements
   5:    end MAIN;

  ----------- cut here ----------

TeleGen2 (tm) Ada Compilation System -- Version 1.4
Copyright 1989 TeleSoft.  All rights reserved.

  File: /usr.MC68020/sparko/1/faculty/mfeldman/telesoft/silly.ada
  Date: 1990-Jun-02 16:54:55

    Front-End            : silly.ada

    Middle-Pass          : main (specification)
    Code-Generator       : main (specification)

    Middle-Pass          : main (body)
     4:         A := ((2,2),(3,3,3), (4,4,4,4));
         
>>> WARNING: Length Check will raise Constraint Error

     4:         A := ((2,2),(3,3,3), (4,4,4,4));
         
>>> WARNING: Length Check will raise Constraint Error

     4:         A := ((2,2),(3,3,3), (4,4,4,4));
         
>>> WARNING: High Check will raise Constraint_Error

     4:         A := ((2,2),(3,3,3), (4,4,4,4));
         
>>> WARNING: Matching Array Length Check will raise Constraint_Error

    Code-Generator       : main (body)

---------------------------------------------------------------------------
Prof. Michael Feldman
Department of Electrical Engineering and Computer Science
The George Washington University
Washington, DC 20052
+1-202-994-5253
mfeldman@seas.gwu.edu
---------------------------------------------------------------------------