diff --git a/Project.toml b/Project.toml
index 4c4453f..8fcea03 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,9 +1,13 @@
 name = "HerbCore"
 uuid = "2b23ba43-8213-43cb-b5ea-38c12b45bd45"
 authors = ["Jaap de Jong <jaapdejong15@gmail.com>", "Nicolae Filat <N.Filat@student.tudelft.nl>", "Tilman Hinnerichs <t.r.hinnerichs@tudelft.nl>", "Sebastijan Dumancic <s.dumancic@tudelft.nl>"]
-version = "0.3.2"
+version = "0.3.3"
+
+[deps]
+AbstractTrees = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"
 
 [compat]
+AbstractTrees = "0.4.5"
 julia = "^1.8"
 
 [extras]
diff --git a/src/HerbCore.jl b/src/HerbCore.jl
index 844cac5..1f7b8f8 100644
--- a/src/HerbCore.jl
+++ b/src/HerbCore.jl
@@ -1,8 +1,10 @@
 module HerbCore
 
+using AbstractTrees
+
+include("grammar.jl")
 include("rulenode.jl")
 include("constraint.jl")
-include("grammar.jl")
 
 export
        AbstractRuleNode,
diff --git a/src/grammar.jl b/src/grammar.jl
index 383dd79..bf1794b 100644
--- a/src/grammar.jl
+++ b/src/grammar.jl
@@ -19,3 +19,11 @@ If the grammar is non-probabilistic, the list can be `nothing`.
 For concrete types, see `ContextSensitiveGrammar` within the `HerbGrammar` module.
 """
 abstract type AbstractGrammar end
+
+function Base.show(io::IO, grammar::AbstractGrammar)
+    for i in eachindex(grammar.rules)
+        println(io, i, ": ", grammar.types[i], " = ", grammar.rules[i])
+    end
+end
+
+Base.getindex(grammar::AbstractGrammar, typ::Symbol) = grammar.bytype[typ]
diff --git a/src/rulenode.jl b/src/rulenode.jl
index 0f02447..5d0c166 100644
--- a/src/rulenode.jl
+++ b/src/rulenode.jl
@@ -16,6 +16,10 @@ Expression trees consist of [`RuleNode`](@ref)s and [`AbstractHole`](@ref)s.
 """
 abstract type AbstractRuleNode end
 
+# Interface to AbstractTrees.jl
+AbstractTrees.children(node::AbstractRuleNode) = get_children(node)
+AbstractTrees.nodevalue(node::AbstractRuleNode) = get_rule(node)
+
 """
     RuleNode <: AbstractRuleNode
 
@@ -36,6 +40,16 @@ mutable struct RuleNode <: AbstractRuleNode
     children::Vector{AbstractRuleNode}
 end
 
+function RuleNode(ind::Int, grammar::AbstractGrammar)
+    RuleNode(
+        ind, nothing, [Hole(get_domain(grammar, type)) for type in grammar.childtypes[ind]])
+end
+
+function RuleNode(ind::Int, _val::Any, grammar::AbstractGrammar)
+    RuleNode(
+        ind, _val, [Hole(get_domain(grammar, type)) for type in grammar.childtypes[ind]])
+end
+
 """
     AbstractHole <: AbstractRuleNode
 
@@ -64,6 +78,11 @@ mutable struct UniformHole <: AbstractUniformHole
     children::Vector{AbstractRuleNode}
 end
 
+function UniformHole(domain::BitVector, grammar::AbstractGrammar)
+    UniformHole(domain,
+        [Hole(get_domain(grammar, type)) for type in grammar.childtypes[findfirst(domain)]])
+end
+
 """
 Hole <: AbstractHole