@type context() :: %{required(binary() | atom()) => value()}

The evaluation context containing variable bindings.

Context maps variable names (strings or atoms) to their values. Both string and atom keys are supported for flexibility.

Examples

%{"score" => 85, "name" => "Alice"}
%{score: 85, name: "Alice"}

@type evaluator_state() :: %{
  instructions: instruction_list(),
  instruction_pointer: non_neg_integer(),
  stack: [value()],
  context: context(),
  halted: boolean()
}

The internal state of the stack machine evaluator.

Contains:

• instructions - list of instructions to execute
• instruction_pointer - current position in instruction list
• stack - evaluation stack (top element is head of list)
• context - variable bindings
• halted - whether execution has stopped

@type instruction() :: [binary() | value()]

A single instruction in the stack machine.

Instructions are lists where the first element is the operation name and remaining elements are arguments.

Currently supported instructions:

• ["lit", value()] - Push literal value onto stack
• ["load", binary()] - Load variable from context onto stack
• ["compare", binary()] - Compare top two stack values with operator
• ["and"] - Logical AND of top two boolean values
• ["or"] - Logical OR of top two boolean values
• ["not"] - Logical NOT of top boolean value
• ["in"] - Membership test (element in collection)
• ["contains"] - Membership test (collection contains element)
• ["add"] - Pop two values, add them, push result
• ["subtract"] - Pop two values, subtract them, push result
• ["multiply"] - Pop two values, multiply them, push result
• ["divide"] - Pop two values, divide them, push result
• ["modulo"] - Pop two values, modulo operation, push result
• ["unary_minus"] - Pop one value, negate it, push result
• ["unary_bang"] - Pop one value, logical NOT it, push result
• ["bracket_access"] - Pop key and object, push object[key] result
• ["object_new"] - Push new empty object onto stack
• ["object_set", binary()] - Pop value and object, set object[key] = value, push object
• ["call", binary(), integer()] - Call built-in function with arguments from stack

Examples

["lit", 42]           # Push literal 42 onto stack
["load", "score"]     # Load variable 'score' from context
["compare", "GT"]     # Pop two values, compare with >, push result
["and"]               # Pop two boolean values, push AND result
["or"]                # Pop two boolean values, push OR result
["not"]               # Pop one boolean value, push NOT result
["add"]               # Pop two values, add them, push result
["subtract"]          # Pop two values, subtract them, push result
["multiply"]          # Pop two values, multiply them, push result
["divide"]            # Pop two values, divide them, push result
["modulo"]            # Pop two values, modulo them, push result
["unary_minus"]       # Pop one value, negate it, push result
["unary_bang"]        # Pop one value, logical NOT it, push result
["bracket_access"]    # Pop key and object, push object[key]
["object_new"]        # Push new empty object onto stack
["object_set", "name"] # Pop value and object, set object["name"] = value, push object
["call", "len", 1]    # Pop 1 argument, call len function, push result

@type instruction_list() :: [instruction()]

A list of instructions that form a complete program.

Instructions are executed in order by the stack machine.

@type internal_result() :: value() | {:error, term()}

The internal result of evaluating a predicate from Evaluator functions.

Returns:

• value() - the final evaluation result value
• {:error, term()} - evaluation error with details

@type location_path() :: [binary() | non_neg_integer()]

Location path for assignment expressions.

Represents the path to an assignable location in nested data structures:

• Simple property: ["user", "name"]
• Array index: ["items", 0, "price"]
• Dynamic property: ["user", "settings", "theme"] (for user.settings["theme"])

@type location_result() :: {:ok, location_path()} | scxml_error()

Result type for location expression evaluation.

Returns:

• {:ok, location_path()} - valid assignment path
• scxml_error() - error if location is not assignable

@type result() :: {:ok, value()} | {:error, term()}

The result of evaluating a predicate from public API functions.

Returns:

• {:ok, value()} - successful evaluation with result value
• {:error, term()} - evaluation error with details

@type scxml_error() ::
  {:error, :undefined_variable, %{variable: binary()}}
  | {:error, :type_mismatch, %{expected: atom(), got: atom()}}
  | {:error, :invalid_location, %{expression: binary()}}
  | {:error, :evaluation_error, %{reason: binary()}}
  | {:error, :parse_error,
     %{message: binary(), line: integer(), column: integer()}}

SCXML-compatible error result for enhanced error handling.

Returns structured error information for SCXML datamodel compatibility:

• {:error, :undefined_variable, %{variable: binary()}} - Variable not found in context
• {:error, :type_mismatch, %{expected: atom(), got: atom()}} - Type mismatch in operation
• {:error, :invalid_location, %{expression: binary()}} - Invalid assignment target
• {:error, :evaluation_error, %{reason: binary()}} - General evaluation error
• {:error, :parse_error, %{message: binary(), line: integer(), column: integer()}} - Parse error

@type scxml_result() :: {:ok, value()} | scxml_error()

SCXML-compatible result type for value expressions.

Returns:

• {:ok, value()} - successful evaluation with result value
• scxml_error() - structured error with SCXML-compatible details

@type value() ::
  boolean()
  | integer()
  | float()
  | binary()
  | list()
  | Date.t()
  | DateTime.t()
  | :undefined

A single value that can be used in predicates.

Values can be:

• boolean() - true/false values
• integer() - integer numeric values
• float() - floating-point numeric values
• binary() - string values
• list() - lists of values
• Date.t() - date values
• DateTime.t() - datetime values
• :undefined - represents undefined/null values