Change isassigned() to match the Base definition

src/ScopedValues.jl

@@ -66,9 +66,14 @@ Base.eltype(::ScopedValue{T}) where {T} = T
 """
     isassigned(val::ScopedValue)
 
-Test if the ScopedValue has a default value.
+Test if the ScopedValue has an assigned value.
 """
-Base.isassigned(val::ScopedValue) = val.has_default
+function Base.isassigned(val::ScopedValue)
+    val.has_default && return true
+    scope = current_scope()::Union{Scope, Nothing}
+    scope === nothing && return false
+    return haskey((scope::Scope).values, val)
+end
 
 const ScopeStorage = HAMT{ScopedValue, Any}
 

test/runtests.jl

@@ -131,6 +131,13 @@ end
     @test ret == 1.23
 end
 
+const sval_uninitialized = ScopedValue{Int}()
+
+@testset "isassigned()" begin
+    @test !isassigned(sval_uninitialized)
+    @with sval_uninitialized => 42 @test isassigned(sval_uninitialized)
+end
+
 @testset "ScopedThunk" begin
     function check_svals()
         @test sval[] == 8