wiki:Commentary/Compiler/Renamer

Version 1 (modified by simonpj, 8 years ago) (diff)

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[ Up: Commentary/Compiler/HscMain ]

The renamer

The renamer's Number One taks is to replace RdrNames with Names. For example, consider

module K where
  f x = True

module N where
  import K

module M where
  import N( f ) as Q
  f = (f, M.f, Q.f, \f -> f)

(where all the variables are RdrNames). The result of renaming module M is:

M.f = (M.f, M.f, K.f, \f_22 -> f_22)

(where all these names are now Names).

  • The top-level unqualifed RdrName "f" has become the External Name M.f.
  • The occurrences "f" and "M.f" are both bound to this Name.
  • The qualified RdrName "Q.f" becomes the Name K.f, because the function is defined in module K.
  • The lambda-bound "f" becomes an Internal name, here written f_22.

(All the External names have uniques too, but we often do not print them.)

In addition, the renamer does the following things:

  • Sort out fixities. The parser parses all infix applications as right-associative, regardless of fixity. For example "a * b + c" is parsed as "a * (b + c)". The renamer re-associates such nested operator applications, using the fixities declared in the module.
  • Dependency analysis for mutually-recursive groups of declarations. This divides the declarations into strongly-connected components.
  • Lots of lexical error checking: variables out of scope, unused bindings, unused imports, patterns that use the same binder many times, etc.