Field Types

Field Types

MashinTalk fields are typed. Types appear in accepts (input contract), responds with (output contract), returns (step output schema), and resource fields (store definitions). The type system is shared across all contexts, with some modifiers specific to stores (see Store Field Types).

When to use

Every field declaration needs a type. Choose the most specific type that matches your data: use integer over number when you know the value is always whole, use enum(...) when the value is one of a fixed set, use decimal for financial amounts where precision matters.

Syntax

<field_name> as <type>, <modifiers>

Primitive types

Type	Description	Example values
text	Text value. The primary string type.	"hello", "[email protected]"
string	Alias for text. Both compile identically.	"hello"
number	Numeric value (integer or floating point). Use when you do not need to distinguish between them.	42, 3.14
integer	Whole number only.	0, 42, -7
decimal	Precise decimal. No floating-point rounding errors. Use for currency, measurements, scores.	19.99, 0.001
boolean	True or false.	true, false
uuid	UUID identifier string. Typically used for primary keys.	"550e8400-e29b-41d4-a716-446655440000"
date	Calendar date without time. ISO 8601 format.	"2026-04-29"
datetime	Date and time in UTC. ISO 8601 format.	"2026-04-29T14:30:00Z"

Composite types

Type	Description	Example
list	List of any values.	[1, "two", true]
list(<type>)	Typed list. All elements must match the inner type.	list(text), list(integer)
map	Key-value map with string keys and any values.	{key: "value", count: 42}
object	Alias for map. Both compile identically.	{name: "test"}
object { ... }	Structured object with named, typed fields. Provides schema validation for nested data.	See examples below.
enum("a", "b", "c")	One of a fixed set of string values. Values are validated on input.	"draft", "active", "archived"
any	Any type. No type validation. Use sparingly.	Any value.

File types

Type	Description	Example
file	Any file. Content-addressed reference.	Binary data reference
file(image)	Image file (any image mime type).	PNG, JPEG, WebP
file(image/png | image/jpeg)	Image restricted to specific formats.	PNG or JPEG only
file(application/pdf)	PDF file.	PDF document
file(text)	Plain text file.	TXT, CSV

File-specific modifiers

Modifier	Description	Example
max_size: <size>	Maximum file size	max_size: 25mb
max_pages: <n>	Maximum page count (PDFs)	max_pages: 100
max_dimensions: <w>x<h>	Maximum image dimensions	max_dimensions: 8000x8000

Special types

Type	Description	Example
machine_ref	Type-safe reference to another machine. Can include schema constraints.	See examples below.

Field modifiers

Modifier	Description	Example
is required	Field must be provided. Cannot be nil.	name as text, is required
default: <value>	Default value if the field is not provided.	count as integer, default: 0

Examples

Input contract with mixed types

machine data_processor

accepts
  query as text, is required
  limit as integer, default: 10
  include_metadata as boolean, default: false
  categories as list(text)
  options as map

responds with
  results as list
  total as integer
  query_time as decimal

Enum for fixed-value fields

accepts
  priority as enum("low", "medium", "high", "critical"), is required
  status as enum("open", "in_progress", "resolved"), default: "open"

Enum values are validated at input. Passing a value not in the set produces a validation error.

Nested objects

accepts
  address as object { street as text, is required; city as text, is required; state as text; zip as text }
  contact as object { name as text, is required; email as text; phone as text }

Nested objects define an inline schema for structured data. Each field inside the object follows the same name as type, modifiers syntax, separated by semicolons.

File inputs

accepts
  receipt as file(image), is required, max_size: 25mb
  report as file(application/pdf), max_pages: 100
  attachment as file

File fields are content-addressed references. The actual bytes are stored once and referenced everywhere. The behavioral ledger stores file metadata (id, content_hash, mime_type, size), never the raw bytes.

Machine references

accepts
  handler as machine_ref, is required
  processor as machine_ref, accepts { text: string }, returns { result: string }

A machine_ref is a type-safe reference to another machine. You can optionally constrain the referenced machine’s input and output schemas. Machine references enable dynamic dispatch: passing different machines as arguments to achieve different behaviors.

Store resource fields

resource product
  id as uuid, is primary_key
  name as text, is required
  price as decimal, is required
  quantity as integer, default: 0
  tags as list(text)
  metadata as map
  status as enum("draft", "active", "discontinued"), default: "draft"
  timestamps

Store fields support the full type system plus store-specific modifiers like is primary_key, column:, and timestamps. See Store Field Types.

Type coercion

MashinTalk applies minimal type coercion at input boundaries:

• String "42" is coerced to 42 for integer and number fields
• String "true" / "false" is coerced to true / false for boolean fields
• ISO 8601 strings are parsed for date and datetime fields

Inside compute step expressions, values are used as-is. No implicit coercion occurs within the expression language.

Governance

Types are structural declarations. They do not involve runtime governance. However, types are part of the machine’s contract and serve several governance purposes:

• Input types are validated before execution starts. Invalid inputs produce a validation error before any steps run.
• Output types are checked after execution. If the machine’s output does not match its declared schema, the execution fails.
• Type information is recorded in the behavioral ledger as part of the execution trace.
• File types track provenance (content hashes, mime types, sizes) in the ledger.

Translations

Types are not translated. They use the same names in all locales. The as keyword and the is modifier keyword are translated:

Language	as	is required
English	as	is required
Spanish	como	es requerido
French	comme	est requis
German	als	ist erforderlich
Japanese	として	必須
Chinese	作为	必填
Korean	으로	필수

See also

• accepts - Input contract declarations
• responds with - Output contract declarations
• Store Field Types - Store-specific field modifiers
• Expression language - How types are used in expressions