Enumerations

Enumerations (or "enums") (spec link) define a closed set of named choices that are considered valid in a specific context. Unlike String inputs that accept any value, enums restrict allowed values so that the execution engine can validate inputs before running a workflow.

Consider a workflow that processes data files in different formats with a format parameter. Using String as the type means invalid values won't be caught until runtime—possibly after hours of execution. Using an enum catches these errors immediately.

wdlCopy
version 1.3

enum DataFormat {
  CSV,
  TSV,
  JSON
}

task parse_data {
  input {
    File infile
    DataFormat format = DataFormat.CSV
  }

  command <<<
    echo "Parsing ~{format} file: ~{infile}"
  >>>
}

workflow process_data {
  input {
    Array[File] files
    DataFormat format
  }

  scatter (file in files) {
    call parse_data {
      infile = file,
      format = format
    }
  }
}

Enum values

Each choice in an enum has an associated value. By default, choices without explicit values are assigned a String value matching the choice name. In the DataFormat example above, DataFormat.CSV has the value "CSV" and DataFormat.JSON has the value "JSON".

You can assign explicit values to choices using =. Values can be any WDL type—primitives, compound types, or even structs.

wdlCopy
version 1.3

# String values (explicit)
enum Color {
  Red = "#FF0000",
  Green = "#00FF00",
  Blue = "#0000FF"
}

# Map values for configuration presets
enum ResourcePreset {
  Small = {"cpu": 2, "memory_gb": 4},
  Medium = {"cpu": 8, "memory_gb": 16},
  Large = {"cpu": 32, "memory_gb": 64}
}

# Array values
enum AnalysisMode {
  Quick = ["--fast", "--no-validation"],
  Standard = ["--validate"],
  Thorough = ["--validate", "--deep-check", "--full-report"]
}

Extracting values with value()

To get the underlying value from an enum choice, use the value() standard library function.

wdlCopy
version 1.3

enum Color {
  Red = "#FF0000",
  Green = "#00FF00",
  Blue = "#0000FF"
}

workflow example {
  Color favorite = Color.Red
  String hex_code = value(favorite)  # "#FF0000"
}

Explicit vs implicit typing

Enums can be explicitly typed by adding a type in square brackets after the name, or implicitly typed by letting WDL infer the type from the values.

wdlCopy
version 1.3

# Explicitly typed as Float—the Int value 3 coerces to Float
enum ExplicitFloat[Float] {
  Three = 3,
  Pi = 3.14159
}

# Implicitly typed—WDL infers Float from the values
enum ImplicitFloat {
  Three = 3.0,
  Pi = 3.14159
}

# Implicitly typed as String (the default when no values are provided)
enum Status {
  Pending,
  Running,
  Complete
}

If values don't coerce to a common type, WDL will report an error:

wdlCopy
# ERROR: Int and String don't coerce to a common type
enum Invalid {
  Number = 42,
  Text = "hello"
}

Comparing enums

Two enum values can be compared for equality using == or !=. To be equal, they must be the same choice of the same enum type.

wdlCopy
version 1.3

enum Priority {
  Low,
  Medium,
  High
}

workflow example {
  Priority level = Priority.High

  Boolean is_high = (level == Priority.High)   # true
  Boolean is_low = (level == Priority.Low)     # false
}

Enum values cannot be compared with ordinal operators (<, >, <=, >=).

String interpolation

When an enum is used in string interpolation, it serializes to its choice name (not its underlying value).

wdlCopy
version 1.3

enum Color {
  Red = "#FF0000"
}

workflow example {
  Color c = Color.Red
  String message = "Selected: ~{c}"        # "Selected: Red"
  String hex = "Hex code: ~{value(c)}"     # "Hex code: #FF0000"
}