package merlin-lib

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package merlin-lib
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Provides type information around the cursor.

The information comes from two sources: 1. enclosing AST nodes: we just retrieve the types in the typedtree 2. if the cursor is on an identifier, by typing it in the current environment

(2) is primarily useful in the following situations:

  • when the identifier is polymorphic in the environment, but monomorphic in the AST because it's been instantiated.
  • when there is a syntax or type error in that area, and we don't have a precise enough AST node for the position (i.e. we got a "recovered" node, of type 'a).

Furthermore, (2) has a finer granularity than (1): when the cursor is in the middle of a longident, e.g. Foo.B|ar.Baz.lol (with | being the cursor), then we'll have one AST node covering the whole ident. But what we reconstruct gives us: Foo.Bar, Foo.Bar.Baz, Foo.Bar.Baz.lol; and we return the type for each of them. These are what we call "small enclosings".

There are however some issues with the small enclosings:

  • one has to be careful of the context (obviously that information won't be available in case of parse errors); because a given identifier could exist in different namespaces, for instance:

    type t
module type t = sig val t : t end
let t (t : t) : (module t) = (module struct let t = t end)
  • the information might be redundant with the one we get from the AST.
val log_section : string