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This patch creates ResultT, a monad transformation used later in
RPC <-> query integration.
Signed-off-by: Agata Murawska <agatamurawska@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

This will allow us to run generic computations in an Applicative
context, if a monadic one is not needed (or not applicable due to
class constraints).
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>

This will allow us to use the simpler applicative form (<$>, <*>)
instead of monadic liftM, liftM2, etc.
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>

Currently, the LookupResult, MatchPriority and related functions are
locate in Loader.hs, since (so far) only hbal needs them in the
selection of instances. However, with the new functionality on confd
side, we need these functions there too, but we don't want to import
Loader.hs (which pulls in lots of balancing-related code). So we move
all these function to BasicTypes.hs, since that module is a leaf one,
with no other dependencies.

Unittests are slightly adjusted (but they are still tested under the
'Loader' group).
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>

While updating the confd code, I realised that we have _lots_ of
duplication in the exit model for the various programs.

So this patch attempts to abstract all the exits via a couple of new
functions; sorry for the somewhat big patch, but I hope the payoff is
worth the change: the actual exit conditions are much clearer.

Note that the patch (also) moves the exitIfBad function to Utils.hs,
since that is more logical.
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

These both are work with/on the Result type, so we add them to
BasicTypes. The functions will be used as more generic versions of
some more specialised functions that are right now spread across the
modules.
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

Following the split Types/BasicTypes, we can remove the last
JSON-related stuff from Utils.hs, and do some more cleanup.
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>

The 'Result' type is common and:

- might be used outside of HTools-specific code too
- is better split as we need these basic types for building the more
  complex ones in Types.hs
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>