# `Tptp.Resolver.Cascade`
[🔗](https://github.com/jcschuster/tptp/blob/v0.1.3/lib/tptp/resolver/cascade.ex#L1)

Tries each of a list of resolvers, in order, and takes the first that answers.

    {Tptp.Resolver.Cascade, resolvers: [Tptp.Resolver.Fs, Tptp.Resolver.Http]}

That composition is the intended one: read from disk when the TPTP distribution
is installed, fall back to tptp.org when it is not. It is still not a default —
it reaches the network, so the caller writes it down.

## What it reports when everything fails

Every resolver's reason, joined, rather than only the last one. "not found in
/opt/TPTP" and "returned 404" are different failures with different fixes, and a
cascade that reported one of them would hide the other.

## `:not_followed` stops the cascade

A resolver that declines has decided, so the cascade decides too. Putting
`Tptp.Resolver.None` in the middle of a list is a way to say "these, and if none
of them, give up quietly" — though the clearer way to say that is to not use a
cascade.

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*Consult [api-reference.md](api-reference.md) for complete listing*