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| extract-hackage-info.cabal | ||
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| README.md | ||
Extract information about packages and operators from Hackage
Introduction
In order to format chains of operator applications nicely, Ormolu needs to be aware of the precedence level (0 to 9) and fixity direction of every infix operator (what we will just call "fixity" in the rest of this document).
In order to build a database of operator fixities, we choose to parse the declarations of every package from Hackage/Hoogle, looking for things of the form:
(++) : [a] -> [a] -> [a]
(that we will call a symbol declaration)
or
infixr 4 ++
(that we will call a fixity declaration)
The second kind of declaration can be exploited directly, because it links an infix operator with a fixity and a source (the package from which the declaration originates).
The first kind, however, doesn't give any fixity information directly. It is
only when there is no matching fixity declaration inside the package files
that a symbol declaration indicates that the operator has the default fixity
(infixl 9).
In general, correct resolution of fixities requires taking into account the import section of a module that is being formatted, as well as knowing the provenance (that is, module name) of each operator. Therefore, we also collect and save this information.
The extract-hackage-info executable takes care of everything listed above,
and generates a hackage-info.bin file containing multi-level map from
package names to module names to operators to their fixities:
newtype HackageInfo
= HackageInfo (Map PackageName (Map ModuleName (Map OpName FixityInfo)))
How to use extract-hackage-info
Run extract-hackage-info.sh from the root of the repository.