A representation of a Haskell Syntax tree that contain source-related and
semantic annotations. These annotations help developer tools to work with the
defined program. The source information enables refactoring and program
transformation tools to change the source code without losing the original
format (layout, comments) of the source. Semantic information helps analyzing
the program. The representation is different from the GHC's syntax tree.
It contains information from all representations in GHC (different version of
syntax trees, lexical and module-level information). The module is split up to
put the representation of different language elements into different modules.
Additionally, it contains the representation of semantic and source
annotations, helper functions and generated instances for the representation of
language elements. Because langauge elements may refer each other (there can be
a pattern inside an expression in case of a pattern match and an expression
inside a pattern if view patterns are enabled), we use hs-boot files to break
up dependency cycles.