Module Merge

module Merge: sig .. end

val merge_envs : TypeCore.env ->
       ?annot:TypeCore.typ ->
       TypeCore.env * TypeCore.var ->
       TypeCore.env * TypeCore.var -> TypeCore.env * TypeCore.var

When the control-flow diverges, one needs to merge the environments, that is, compute a set of permissions that subsumes the two environments. In order to run, the merge_envs function takes:

• a top environment which represents the original environment before the control-flow started to diverge,
• an optional type annotation which may contain a list of expected permissions to be available after this merge operation
• a pair of the left environment, and the variable that represents the return value computed in the left environment
• the same thing for the right environment.

It returns a merged environment along with a variable that points to the combined return value of the merged environment.

Consider for example "if True then x else y"; the combined return value of the two environments will try to reconcile the permissions available for "x" and "y".