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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/exts/template_haskell.rst | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/docs/users_guide/exts/template_haskell.rst b/docs/users_guide/exts/template_haskell.rst index a97f9a8f6b..f1319b904e 100644 --- a/docs/users_guide/exts/template_haskell.rst +++ b/docs/users_guide/exts/template_haskell.rst @@ -542,6 +542,30 @@ Run :file:`main` and here is your output: $ ./main Hello +.. _th-rs: + +Template Haskell quotes and Rebindable Syntax +--------------------------------------------- + +Rebindable syntax does not play well with untyped TH quotes: +applying the rebindable syntax rules would go against the lax +nature of untyped quotes that are accepted even in the presence of +unbound identifiers (see :ghc-ticket:`18102`). Applying the rebindable syntax +rules to them would force the code that defines the said quotes to have all +the necessary functions (e.g ``ifThenElse`` or ``fromInteger``) in scope, +instead of delaying the resolution of those symbols to the code that splices +the quoted Haskell syntax, as is usually done with untyped TH. For this reason, +even if a module has untyped TH quotes with ``RebindableSyntax`` enabled, GHC +turns off rebindable syntax while processing the quotes. The code that splices +the quotes is however free to turn on ``RebindableSyntax`` to have the usual +rules applied to the resulting code. + +Typed TH quotes on the other hand are perfectly compatible with the eager +application of rebindable syntax rules, and GHC will therefore process any +such quotes according to the rebindable syntax rules whenever the +``RebindableSyntax`` extension is turned on in the modules where such quotes +appear. + .. _th-profiling: Using Template Haskell with Profiling |