Update abstract interpreter docs.

docs/src/ref/absint.md

@@ -1,3 +1,24 @@
 # Abstract Interpretation
 
-Coming soon!
+PDDL.jl supports [abstract interpretation](https://en.wikipedia.org/wiki/Abstract_interpretation) of PDDL domains, the semantics of which can also be compiled using the [PDDL.jl compiler](compiler.md). This functionality is exposed by the [`abstracted`](@ref) and [`abstractstate`](@ref) functions:
+
+```@docs
+abstracted
+abstractstate
+```
+
+The behavior of the abstract interpreter can be customized by specifying the Julia type used to represent abstract values for a particular fluent or PDDL type:
+
+```@docs
+PDDL.AbstractInterpeter
+```
+
+## Abstract Values and Types
+
+Abstract interpretation requires each concrete value to be mapped to an abstract value of a particular type, which represents an (over-approximation) of the set of the possible values reachable after a series of actions have been executed. By default, Boolean values (i.e. predicates) are mapped to the [`BooleanAbs`](@ref) abstraction, while scalar numbers (corresponding to PDDL types like `integer`, `number` and `numeric`) are mapped to the [`IntervalAbs`](@ref) abstraction. Other types of values may use the [`SetAbs`](@ref) abstraction.
+
+```@docs
+PDDL.BooleanAbs
+PDDL.IntervalAbs
+PDDL.SetAbs
+```

docs/src/ref/compiler.md

@@ -1,5 +1,7 @@
 # Compiler
 
+PDDL.jl supports compilation of the semantics of PDDL domains through code-generation for PDDL actions and custom datatypes for PDDL states. See [Speeding Up PDDL.jl](../tutorials/speeding_up.md) for a more detailed explanation.
+
 ```@docs
 compiled
 compilestate

src/abstractions/boolean.jl

@@ -21,7 +21,9 @@ isboth(b) = false
 """
     BooleanAbs
 
-Belnap logic abstraction for Boolean values.
+Belnap logic abstraction for Boolean values. In addition to `true`, `false` and
+`missing`, the abstract value `both` can be used to represent when a predicate
+is both false and true.
 """
 const BooleanAbs = Union{Missing,Bool,Both}
 

src/interpreter/abstract/abstract.jl

@@ -2,7 +2,7 @@
 
 """
     AbstractInterpreter(
-        type_abstractions = default_abstypes(),
+        type_abstractions = PDDL.default_abstypes(),
         fluent_abstractions = Dict(),
         autowiden = false
     )