Type System

Graphyn uses a WorkflowType sealed interface to describe what kind of data flows through a port. The type system is checked when a user draws a connection — incompatible types are rejected with a visual toast.

Type variants

sealed interface WorkflowType {
    data object StringType  : WorkflowType
    data object IntType     : WorkflowType
    data object DoubleType  : WorkflowType
    data object BooleanType : WorkflowType
    data object OpaqueType  : WorkflowType          // accepts any incoming type

    data class ListType(val elementType: WorkflowType) : WorkflowType
    data class NullableType(val wrappedType: WorkflowType) : WorkflowType
    data class RecordType(val fields: Map<String, WorkflowType>) : WorkflowType
    data class EnumType(val values: List<String>) : WorkflowType
    data class MultiEnumType(val values: List<String>) : WorkflowType
}

Primitive types

Type	Kotlin equivalent	Example value
`StringType`	`String`	`WorkflowValue.StringValue("hello")`
`IntType`	`Int`	`WorkflowValue.IntValue(42)`
`DoubleType`	`Double`	`WorkflowValue.DoubleValue(3.14)`
`BooleanType`	`Boolean`	`WorkflowValue.BooleanValue(true)`

Structural types

ListType(elementType) — a homogeneous list.

WorkflowType.ListType(WorkflowType.StringType)   // List<String>
WorkflowType.ListType(WorkflowType.OpaqueType)   // List<Any>

RecordType(fields) — a named map of typed fields, similar to a JSON object or a data class.

WorkflowType.RecordType(mapOf(
    "name"  to WorkflowType.StringType,
    "score" to WorkflowType.DoubleType,
))

NullableType(wrappedType) — wraps any type to indicate the value may be absent.

WorkflowType.NullableType(WorkflowType.StringType)  // String?

In the FieldCard UI, nullable ports render a checkbox that toggles between null and the inner type's default value.

EnumType(values) — a single-choice dropdown from a fixed list of string options.

WorkflowType.EnumType(listOf("GET", "POST", "PUT", "DELETE"))

MultiEnumType(values) — a multi-choice variant of EnumType.

OpaqueType

OpaqueType is a structural wildcard — it accepts an incoming connection of any type. Use it for pass-through ports, union operations, or when the concrete type is determined at runtime.

PortSpec("value", WorkflowType.OpaqueType)  // accepts String, Int, Record, List, etc.

Only use OpaqueType when the node genuinely cannot know the type in advance. Over-using it defeats type safety and removes all editor feedback for the user.

Compatibility rules

A connection from output port O to input port I is accepted when:

Input port type	Accepts
`OpaqueType`	any output type
`StringType`	`StringType` only
`IntType`	`IntType` only
`DoubleType`	`DoubleType` only
`BooleanType`	`BooleanType` only
`ListType(E)`	`ListType(E)` where E matches
`NullableType(T)`	`T` or `NullableType(T)`
`RecordType(F)`	`RecordType(F)` with same field names and matching field types
`EnumType(V)`	`EnumType(V)` with same values list

Type checking runs in WorkflowTypeCompatibility.isCompatible(outputType, inputType) in the core module.

`displayName()` extension

fun WorkflowType.displayName(): String

Returns a human-readable label shown in port tooltips and the inspector:

Type	`displayName()`
`StringType`	`"String"`
`IntType`	`"Int"`
`ListType(StringType)`	`"List<String>"`
`NullableType(IntType)`	`"Int?"`
`RecordType(...)`	`"Record"`
`OpaqueType`	`"Any"`

WorkflowValue

Every port value at runtime is a WorkflowValue:

sealed interface WorkflowValue {
    data class StringValue(val value: String)    : WorkflowValue
    data class IntValue(val value: Int)          : WorkflowValue
    data class DoubleValue(val value: Double)    : WorkflowValue
    data class BooleanValue(val value: Boolean)  : WorkflowValue
    data class ListValue(val items: List<WorkflowValue>) : WorkflowValue
    data class RecordValue(val fields: Map<String, WorkflowValue>) : WorkflowValue
    data object NullValue : WorkflowValue
}

NullValue is the runtime representation of a NullableType port with no value set.