I do not understand "not portable" here. Do you mean that some architectures don't support TH?
Template Haskell doesn't play nicely with cross compilation [1] or stage-1 compilers, so Template Haskell is simply a non-starter for a lot of uses. It's why the GHC codebase and boot libraries largely don't use the -XTemplateHaskell extension (aside from the test suite, of course).
What staging issues?
I'm imagining here having `deriving Blah` be surface syntax that desugars into some TH splice. You keep the nice user-facing syntax, but make the deriving mechanism itself specified in TH code.
That won't currently work with the way TH stages its splices. For example, the following code: {-# LANGUAGE PackageImports, TemplateHaskell #-} import "deriving-compat" Data.Eq.Deriving bar :: Bar bar = Bar data Foo = Foo $(deriveEq ''Foo) data Bar = Bar $(deriveEq ''Bar) will fail to compile because of the staging restrictions on Template Haskell splices, whereas replacing the splices with `deriving Eq` would make it compile.
It's an interesting idea, but one probably best tackled after the current proposal.
Completely agreed. :) Ryan S. ----- [1] https://ghc.haskell.org/trac/ghc/wiki/TemplateHaskell/CrossCompilation