Re: Incomplete value at Symbol.cc:130

[Dr . Jürgen Sauermann]

    Hi Hans-Peter,
      
      thanks a lot for your feedback. See my comments below.
      
      Best Regards,
      Jürgen

On 12/14/20 4:39 PM, Hans-Peter Sorge wrote:

>       
>       Hi,
>       
>       I could not resist to experiment.....
>       
>             )clear
>       CLEAR WS     
>               A←0
>               A.A←1
>       DOMAIN ERROR+
>               A.A←1
>                ^ ^
>       
>             )clear
>       CLEAR WS
>             A.A←1
>             A←0      ⍝ Just replacing content of A.    
>            
>             B.B←2
>             A←B.B    ⍝ Generates a trace. - probably should be A.B ←→ 2 
>        
>       
>       Incomplete value at Symbol.cc:130
>         Addr:    0x1ce1990
>         Rank:    0
>         ..............
>       
>     
    Fixed in SVN 1377.
    
>  ⍝ A
>       structured variable of any depth can be replaced by an assignment
>       to the root variable.
>             A.B.C.D←4
>             A
>       .B:
>       .B.C:
>       .B.C.D: 4
>       
>             A←1   ⍝ Consistent with current assignment: replace variable
>       content with RV. No DOMAIN ERROR.
>             A
>       1
>       
>       
>       ⍝ Assignment working one time only ..
>       
>             A.B.C ←1
>             X.Y.Z ←2
>             A.B.C←X.Y
>             A
>       .B:
>       .B.C:
>       .B.C.Z: 2
>       
>       ⍝ should be repeatable:
>             A.B.C←X.Y
>       DOMAIN ERROR+
>             A.B.C←X.Y
>                ^   ^
>       
>     
    Actually no.
    
    A.B.C←X.Y turns leaf A.B.C into a non-leaf, therefore an assignment
    to it it gives you DOMAIN ERROR.
>       Proposal:
>       
>       Allow a non-leaf node to be replaced by a RV. it would then be
>       consistent with how the current assignment works.    
>       
>     
    I was thinking of this myself quite a bit. My current thoughts are
    that overriding a non-leaf can
    destroy an arbitrary number of sub-variables, just like rm -R /
    and common *nix- wisdom has it that
    this should be refused and that rm -Rf should be required
    instead. I actually spent a very long
    night at the end of the 1970s after my boss did rm -R / by
    mistake. The counter-argument is that
    you can erase arbitrary large non-structured values with an
    assignment in APL.
    
    I also believe that assignment to a non-leaf is an implicit ⎕EX of
    the non-leaf which is not
    consistent with plain variable assignment. In plain variable
    assignments, you can create a
    variable and change a variable, but not erase a variable. That
    requires an explicit ⎕EX or )ERASE.
    
    Above A.B.C is a (sub-) variable with value Z, so you can change it
    as long as it is a leaf (including
    changing it to the value of another structured variable X.Y ←→ Z).
    But overriding it after it has
    become a non-leaf is not allowed because that would implicitly ⎕EX
    it (which in the case of
    plain variables is not possible resp. requires ⎕EX or )ERASE).
    
    The model here is that ABC behaves like a variable but A.B does not
    (it is a collection of variables
    and the questions is essentially whether it should be possible to
    override several (sub-) variables
    by a single assignment).
    
    I belive both alternatives have arguments speaking for them and I
    would like to hear more opinions
    before allowing assignments to non-leaf sub-variables.
>  The
>       assignment above "A.B.C ← X.Y" is actually an append -> A.B.C.Z
>       rather than a replace,  what a "←" normally does.
>       
>       I think the assignment should result in A.B.C ← X.Y.  ←→ A.B.Z
>       
>     
    It probably would if the assignment were legal.
>  The
>       append could be covered by the idiom  A.B.C. ← X.Y.   ←→ A.B.C.Z
>                     
>       .. just my thoughts.
>         
>             A.B.C ←1
>               X.Y.Z ←2
>               K.L.M ←3
>         
>               A.B.C ← X.Y K.L
>         DOMAIN ERROR+
>               A.B.C←X.Y K.L
>                  ^   ^
>         'Idea:'
>               A.B.C ← X.Y. K.L.   ←→ A.B.Z  A.B.M
>         and:      
>               A.B.C. ← X.Y. K.L.   ←→ A.B.C.Z  A.B.C.M 
>               
>       
>       Basically saying:
>       Using a trailing dots lets operators work with a structured name
>       element.
>       A.B. ←→ C
>       
>       given
>           A.B.a←1 ⋄ A.B.b←2 ⋄ A.B.c←3
>         X.Y.x←10 ⋄ X.Y.y←20 ⋄
>               X.Y.z←30
>             
>           A.B. could result in structured name elements a b c. That is
>           listing the leaf-node names.  
>           A.B. ← X.Y.  could
>               result in structured names A.B.x, A.B.y, A.B.z
>         
>       
>       
>       Without trailing dots we get the content of a variable.
>       A.B.C  ←→ 1 
>        
>             A.B.a←1
>             A.B.b←2
>             A.B.c←3
>             A
>             A.B
>       .a: 1
>       
>       .b: 2
>       
>       .c: 3
>       
>             A.B + 1
>       DOMAIN ERROR
>             A.B+1
>              ^ ^
>       ⍝ could be
>             A.B + 1
>       2 3 4
>       
>       
>       Sorry for the lengthy note.  
>       
>       Best Regards
>       Hans-Peter
>       
>