diff --git a/Project.toml b/Project.toml
index 9f9d5d3..dee6611 100644
--- a/Project.toml
+++ b/Project.toml
@@ -20,7 +20,7 @@ HerbConstraints = "^0.2.0"
 HerbCore = "^0.3.0"
 HerbGrammar = "^0.4.0"
 HerbInterpret = "^0.1.3"
-HerbSpecification = "^0.1.0"
+HerbSpecification = "0.2"
 MLStyle = "^0.4.17"
 Random = "1.8.0,1.9.0,1.10.0,1.11.0"
 StatsBase = "^0.34"
diff --git a/src/evaluate.jl b/src/evaluate.jl
index 6fa4db1..79a160d 100644
--- a/src/evaluate.jl
+++ b/src/evaluate.jl
@@ -18,7 +18,13 @@ Optional parameters:
 
 Returns a score in the interval [0, 1]
 """
-function evaluate(problem::Problem{Vector{IOExample}}, expr::Any, symboltable::SymbolTable; shortcircuit::Bool=true, allow_evaluation_errors::Bool=false)::Number
+function evaluate(
+    problem::Problem{<:AbstractVector{<:IOExample}},
+    expr::Any,
+    symboltable::SymbolTable;
+    shortcircuit::Bool=true,
+    allow_evaluation_errors::Bool=false
+)::Number
     number_of_satisfied_examples = 0
 
     crashed = false
diff --git a/src/stochastic_iterator.jl b/src/stochastic_iterator.jl
index e678bd3..b8ae243 100644
--- a/src/stochastic_iterator.jl
+++ b/src/stochastic_iterator.jl
@@ -157,7 +157,7 @@ end
 
 Returns the cost of the `program` using the examples and the `cost_function`. It first convert the program to an expression and evaluates it on all the examples.
 """
-function _calculate_cost(program::Union{RuleNode, StateHole}, cost_function::Function, spec::AbstractVector{IOExample}, grammar::AbstractGrammar, evaluation_function::Function)
+function _calculate_cost(program::Union{RuleNode, StateHole}, cost_function::Function, spec::AbstractVector{<:IOExample}, grammar::AbstractGrammar, evaluation_function::Function)
     results = Tuple{<:Number,<:Number}[]
 
     expression = rulenode2expr(program, grammar)
diff --git a/test/test_search_procedure.jl b/test/test_search_procedure.jl
index 965e231..ec46879 100644
--- a/test/test_search_procedure.jl
+++ b/test/test_search_procedure.jl
@@ -32,7 +32,7 @@
             Index = List[Number]
         end
         
-        problem = Problem([IOExample(Dict(), x) for x ∈ 1:5])
+        problem = Problem([IOExample(Dict{Symbol,Any}(), x) for x ∈ 1:5])
         iterator = BFSIterator(g₂, :Index, max_depth=2)
         solution, flag = synth(problem, iterator, allow_evaluation_errors=true)
 
@@ -70,7 +70,7 @@
             Index = List[Number]
         end
         
-        problem = Problem([IOExample(Dict(), x) for x ∈ 1:5])
+        problem = Problem([IOExample(Dict{Symbol,Any}(), x) for x ∈ 1:5])
         iterator = BFSIterator(g₃, :Index, max_depth=2)
         solution, flag = synth(problem, iterator, allow_evaluation_errors=true)