Sum of single element substitution rules looks wrong to me

[leo-brewin]

Here is a short Cadabra fragment

foo1 := {A->B}.
foo2 := {A->B,B->C}.

bah1 := {D->E}.
bah2 := {D->E,E->F}.

print(foo1+bah1)
print(foo1+bah2)
print(foo2+bah1)
print(foo2+bah2)

print(foo1 + Ex(",,") + bah1)

This produces the following output

A -> B + D -> E
{A -> B, D -> E, E -> F}
{A -> B, B -> C, D -> E}
{A -> B, B -> C, D -> E, E -> F}
{A -> B, D -> E}

The first line (a sum of two single element rule) looks wrong. I think it should look the same as the final line of output.

[kpeeters]

That's because, for historical reasons, it is not the curly brackets that lead to the creation of a list, but the comma. So bah1 is not a list, it is a single expression.

I could probably change this now, but it may trigger weird other problems. I'll keep the issue open.

[leo-brewin]

Hi Kasper, Thanks for the explanation. I think I'll avoid this problem by rewriting that section of the tutorial to not involve adding single element rules. I'll change the example to be a sum of four rules (which I can split into the sum of two lists).

[kpeeters]

For reference: you can generate a single-item list with

foo1 := {A->B, {}}

or

foo1:= \comma{A}

[leo-brewin]

HI Kasper,

My apologies for not replying sooner (I got distracted with other stuff).

Thanks for the update. Your solution is similar to what I’ve been using which was to include a trivial rule such as foo1 := {A->B, x->x} Cheers, Leo

On 24 Sep 2019, at 7:22 am, Kasper Peeters [email protected] wrote:

That's because, for historical reasons, it is not the curly brackets that lead to the creation of a list, but the comma. So bah1 is not a list, it is a single expression.

I could probably change this now, but it may trigger weird other problems. I'll keep the issue open.

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