If you write the literal in a string, apply 'read' and specify the type, then it should work.
If you write it in a string literal, then it might be that you need to use defaulting to get it to evaluate to Crust.
If you write just a bare <...> in ghci then afaik that won't ever work, as there's a fixed set of literals ghc's parser accepts.
I've written my own Read and Show instances for a type, which is essentially
data Crust a = Open [a] | Closed [a]
"Show" does something like
*Main> Closed [1,2,3]
*Main> Open [1,2,3]
And Read faithully parses each stings and turns it into a Crust again.
Problem is: when I just type <1,2,3..> in GHCi I get a "parse error on input ‘<’". However when I spell out the
custructor as above it parses it okay.
Is it possible at all to write my own <> constructor, or something like it=
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