diff --git a/src/code_gen/tape_machine.jl b/src/code_gen/tape_machine.jl
index f1391b1..94b9f54 100644
--- a/src/code_gen/tape_machine.jl
+++ b/src/code_gen/tape_machine.jl
@@ -1,3 +1,4 @@
+#=
 # TODO: do this with macros
 function call_fc(
     fc::FunctionCall{VectorT,0}, cache::Dict{Symbol,Any}
@@ -49,8 +50,9 @@ function call_fc(fc::FunctionCall{VectorT,M}, cache::Dict{Symbol,Any}) where {Ve
     )
     return nothing
 end
+=#
 
-function expr_from_fc(fc::FunctionCall{VAL_T,N_ARG,N_RET}) where {VAL_T,N_ARG,N_RET}
+function expr_from_fc(fc::FunctionCall{VAL_T}) where {VAL_T}
     if length(fc) == 1
         func_call = Expr(
             :call,
@@ -92,9 +94,9 @@ function gen_input_assignment_code(
             fc = FunctionCall(
                 context_module.eval(Expr(:->, :x, input_expr(instance, name, :x))),
                 (),
-                (:input,),
-                (symbol,),
-                (Nothing,),
+                [:input],
+                [symbol],
+                [Nothing],
                 device,
             )
 
@@ -203,8 +205,8 @@ function _closure_fc(
     setdiff!(arg_symbols_set, ret_symbols_set)
     intersect!(ret_symbols_set, undefined_argument_symbols)
 
-    arg_symbols_t = (arg_symbols_set...,)
-    ret_symbols_t = (ret_symbols_set...,)
+    arg_symbols_t = [arg_symbols_set...]
+    ret_symbols_t = [ret_symbols_set...]
 
     closure = context_module.eval(
         Expr(                                   # create the closure: () -> code block; return (locals)
diff --git a/src/devices/impl.jl b/src/devices/impl.jl
index 1c31f46..35236c2 100644
--- a/src/devices/impl.jl
+++ b/src/devices/impl.jl
@@ -33,19 +33,21 @@ end
 
 Dispatch from the given [`FunctionCall`](@ref) to the interface function [`_gen_access_expr`](@ref).
 """
-function gen_access_expr(fc::FunctionCall{VAL_T,N_ARG,N_RET}) where {VAL_T,N_ARG,N_RET}
-    vec = Expr[]
-    for ret_symbols in fc.return_symbols
-        push!(vec, unroll_symbol_vector(_gen_access_expr.(Ref(fc.device), ret_symbols)))
+function gen_access_expr(fc::FunctionCall{VAL_T}) where {VAL_T}
+    if length(fc.return_types) != 1
+        # general case
+        vec = Expr[]
+        for ret_symbols in fc.return_symbols
+            push!(vec, unroll_symbol_vector(_gen_access_expr.(Ref(fc.device), ret_symbols)))
+        end
+        if length(vec) > 1
+            return unroll_symbol_vector(vec)
+        else
+            return vec[1]
+        end
     end
-    if length(vec) > 1
-        return unroll_symbol_vector(vec)
-    else
-        return vec[1]
-    end
-end
 
-function gen_access_expr(fc::FunctionCall{VAL_T,N_ARG,1}) where {VAL_T,N_ARG}
+    # no vectorization case
     vec = Symbol[]
     for ret_symbols in fc.return_symbols
         push!(vec, _gen_access_expr.(Ref(fc.device), ret_symbols[1]))
diff --git a/src/scheduler/type.jl b/src/scheduler/type.jl
index 4a441c6..03fc918 100644
--- a/src/scheduler/type.jl
+++ b/src/scheduler/type.jl
@@ -5,24 +5,25 @@ Type representing a function call. Contains the function to call, argument symbo
 
 TODO: extend docs
 """
-mutable struct FunctionCall{VAL_T<:Tuple,N_ARG,N_RET}
+mutable struct FunctionCall{VAL_T<:Tuple}
     func::Function
-    value_arguments::Vector{VAL_T}                          # tuple of value arguments for the function call, will be prepended to the other arguments
-    arguments::Vector{NTuple{N_ARG,Symbol}}                 # symbols of the inputs to the function call
-    return_symbols::Vector{NTuple{N_RET,Symbol}}            # the return symbols
-    return_types::NTuple{N_RET,Type}                        # the return type of the function call(s); there can only be one return type since we require type stability
+    value_arguments::Vector{VAL_T}          # tuple of value arguments for the function call, will be prepended to the other arguments
+    arguments::Vector{Vector{Symbol}}       # symbols of the inputs to the function call
+    return_symbols::Vector{Vector{Symbol}}  # the return symbols
+    return_types::Vector{<:Type}              # the return type of the function call(s); there can only be one return type since we require type stability
     device::AbstractDevice
 end
 
 function FunctionCall(
     func::Function,
     value_arguments::VAL_T,
-    arguments::NTuple{N_ARG,Symbol},
-    return_symbol::NTuple{N_RET,Symbol},
-    return_types::NTuple{N_RET,Type},
+    arguments::Vector{Symbol},
+    return_symbol::Vector{Symbol},
+    return_types::Vector{<:Type},
     device::AbstractDevice,
-) where {VAL_T<:Tuple,N_ARG,N_RET}
+) where {VAL_T<:Tuple}
     # convenience constructor for function calls that do not use vectorization, which is most of the use cases
+    @assert length(return_types) == 0 || length(return_types) == length(return_symbol) "number of return types $(length(return_types)) does not match the number of return symbols $(length(return_symbol))"
     return FunctionCall(
         func, [value_arguments], [arguments], [return_symbol], return_types, device
     )
diff --git a/src/task/compute.jl b/src/task/compute.jl
index 39c2092..07559d9 100644
--- a/src/task/compute.jl
+++ b/src/task/compute.jl
@@ -12,7 +12,7 @@ function get_function_call(
     in_symbols::NTuple{N,Symbol},
     out_symbol::Symbol,
 ) where {N}
-    return FunctionCall(compute, (t,), in_symbols, (out_symbol,), (Any,), device)
+    return FunctionCall(compute, (t,), [in_symbols...], [out_symbol], [Any], device)
 end
 
 function get_function_call(node::ComputeTaskNode)
@@ -37,9 +37,9 @@ function get_function_call(node::DataTaskNode)
     return FunctionCall(
         identity,
         (),
-        (Symbol(to_var_name(first(children(node))[1].id)),),
-        (Symbol(to_var_name(node.id)),),
-        (Any,),
+        [Symbol(to_var_name(first(children(node))[1].id))],
+        [Symbol(to_var_name(node.id))],
+        [Any],
         first(children(node))[1].device,
     )
 end
@@ -50,9 +50,9 @@ function get_init_function_call(node::DataTaskNode, device::AbstractDevice)
     return FunctionCall(
         identity,
         (),
-        (Symbol("$(to_var_name(node.id))_in"),),
-        (Symbol(to_var_name(node.id)),),
-        (Any,),
+        [Symbol("$(to_var_name(node.id))_in")],
+        [Symbol(to_var_name(node.id))],
+        [Any],
         device,
     )
 end
@@ -63,33 +63,12 @@ function _argument_types(known_res_types::Dict{Symbol,Type}, fc::FunctionCall)
 end
 
 function result_types(
-    fc::FunctionCall{VAL_T,N_ARG,1}, known_res_types::Dict{Symbol,Type}
-) where {VAL_T,N_ARG}
+    fc::FunctionCall{VAL_T}, known_res_types::Dict{Symbol,Type}
+) where {VAL_T}
     arg_types = (_value_argument_types(fc)..., _argument_types(known_res_types, fc)...)
     types = Base.return_types(fc.func, arg_types)
 
-    if length(types) > 1
-        throw(
-            "failure during type inference: function call $fc with argument types $(arg_types) is type unstable, possible return types: $types",
-        )
-    end
-    if isempty(types)
-        throw(
-            "failure during type inference: function call $fc with argument types $(arg_types) has no return types, this is likely because no method matches the arguments",
-        )
-    end
-    if types[1] == Any
-        @warn "inferred return type 'Any' in task $fc with argument types $(arg_types)"
-    end
-
-    return (types[1],)
-end
-
-function result_types(
-    fc::FunctionCall{VAL_T,N_ARG,N_RET}, known_res_types::Dict{Symbol,Type}
-) where {VAL_T,N_ARG,N_RET}
-    arg_types = (_value_argument_types(fc)..., _argument_types(known_res_types, fc)...)
-    types = Base.return_types(fc.func, arg_types)
+    N_RET = length(fc.return_types)
 
     if length(types) > 1
         throw(
@@ -104,11 +83,15 @@ function result_types(
     if types[1] == Any
         @warn "inferred return type 'Any' in task $fc with argument types $(arg_types)"
     end
+
+    if (N_RET == 1)
+        return [types[1]]
+    end
+
     if !(types[1] isa Tuple) || length(types[1].parameters) != N_RET
         throw(
             "failure durng type inference: function call $(fc.func) was expected to return a Tuple with $N_RET elements, but returns $(types[1])",
         )
     end
-
-    return (types[1].parameters...,)
+    return [types[1].parameters...]
 end