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Type Inference
This module is used for two things that overlap:
inferring the types of symbols that have not been declared (e.g. in "fof" or "cnf" TPTP statements) so as to enrich a Signature
converting untyped terms or formulas into typed formulas, by inferring the exact type of each subterm (and possibly inferring type parameters).
In this context, generalizing type variables means that if some ID.t whose type was unknown and its type still contains variables after the type inference, those variables are quantified instead of being bound to a default type (typically .Type.i).
For instance: say f is not declared and occurs in the term f(f(nil)) with the declared constructor nil : list(A). The inferred type for f should be something like list(B) -> list(B).
If we generalize, we declare that f : list(A) -> list(A) (for all A).
If we don't, we declare that f : list($i) -> list($i).
Here we use a single scope when we unify and substitute type variables, the scope 0.
Many functions will use an Error monad to make errors explicit. The error type is or_error. The module CCError in containers can be used to deal with errors (including monadic operators).
This module provides a typing context, with an applicative interface. The context is used to map terms to types locally during type inference. It also keeps and updates a signature when symbols' types are inferred.
This module is quite low-level, and shouldn't be used in simple cases (see the following modules)
This module, abstract in the exact kind of term it types, takes as input a signature and an untyped term, and updates the typing context so that the untyped term can be converted into a typed term.
infer_statement ctx ~f st checks and convert st into a typed statements, and a list of auxiliary type declarations for symbols that were inferred implicitly.