disallow repeated substrates or products in reactions

[isaacsas]

From https://discourse.julialang.org/t/read-in-network-does-not-match-hard-coded-network/81997/5

rx = @reaction k, A+A --> B
@parameters k
@variables t A(t) B(t)
rx2 = Reaction(k, [A,A], [B], [1,1], [1])
rx != rx2   # true

We need an error check here (perhaps with a kwarg to disable), or need to detect this and correct the substrates/products.

[TorkelE]

While I agree

rx = @reaction k, 2A --> B

is much better than

rx = @reaction k, A+A --> B

is there a strong reason to disallow the latter?

[isaacsas]

We support both notations via the DSL. The issue is in symbolically building Reactions -- they currently assume their inputs are unique, and I think they should stay that way for internal use. So we either need an error check in their constructor or we need to normalize them in the constructor by merging repeated species.