Error Reference

The hierarchy

Every failure Sense can raise is a SenseError subclass, each carrying a source line number when one is known:

SenseError
  SenseSyntaxError    lexer or parser: malformed source
  SenseNameError      an identifier isn't defined in the current scope
  SenseTypeError      a value doesn't match a declared type annotation
  SenseRuntimeError   everything else at runtime
  SenseImportError    module resolution / circular import failures
  SensePolicyError    an Action's required capability was denied
  SenseApprovalError  an Action declared `requires approval` was
                      committed before <action>.approve() was called

A Sense program should never surface a raw Python traceback for a user-level mistake. Every error path in the interpreter is designed to raise one of these, with a message that says what went wrong and, where useful, what to do about it.

How the CLI presents them

sense run broken.sns

SenseError: [line 3] cannot assign value of type String to 'x: Int'

exit code 1. A RecursionError (Python’s own stack-overflow signal, for deeply recursive Sense programs) is caught separately and presented as SenseError: maximum recursion depth exceeded rather than a raw traceback.

Errors with a distinct “did you mean” message

A handful of lexer errors are deliberately more specific than “unexpected character,” aimed at people (and LLMs) whose habits default to another language’s syntax:

You typed	You get
`{` or `}`	”Sense uses indentation for blocks, not `{ }` — write `:` then an indented block instead”
`;`	”semicolons aren’t used in Sense — start a new line instead”
`!` (alone)	”’!’ is not an operator in Sense — use ‘not’ for negation and ’!=’ for not-equal”
a bare `name(...) returns Type:` with no `def`	”function declarations need ‘def’ — e.g. ‘def name(…) -> Type:‘“
`name(...): ... compensate:`	“‘compensate’ is now spelled ‘rollback’ — rename this block’s leading word to ‘rollback:‘“
a tab used for indentation	”tabs are not allowed for indentation — use spaces”

Common runtime errors, by cause

Type mismatch on a typed declaration or function boundary

x: Int = "nope", or calling f(a: Int) with a String, or a function declared returns Int that returns a String. See Values & Types.

Undefined variable

Reading a name nothing in the enclosing scope chain ever bound. See Variables & Scope.

Division or modulo by zero

1 / 0 and 1 % 0 both raise — Sense never returns inf/nan silently.

Wrong number of arguments

Every declared function/action parameter must be supplied exactly once per call — no defaults, no variadic user-defined functions yet.

Action lifecycle violations

.commit() before .verify(), verifying or committing twice, calling start() on an already-started agent, resume() on a non-paused agent — see Actions and Pause & Resume.

Policy denial

SensePolicyError specifically — an action’s requires capability was denied by the nearest applicable policy rule. See Policy.

Missing approval

SenseApprovalError specifically — an action declared requires approval was .commit()-ted before <action>.approve() was ever called. See Actions.

Circular or missing import

SenseImportError, naming the cycle or the resolved path that wasn’t found. See Modules.

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Builtins reference

What each builtin raises and when.

CLI reference

How sense run/sense repl behave around errors.

Look something up

Examples

Error Reference

The hierarchy

How the CLI presents them

Errors with a distinct “did you mean” message

Common runtime errors, by cause

Continue

Builtins reference

CLI reference

​The hierarchy

​How the CLI presents them

​Errors with a distinct “did you mean” message

​Common runtime errors, by cause

​Continue

Builtins reference

CLI reference

The hierarchy

How the CLI presents them

Errors with a distinct “did you mean” message

Common runtime errors, by cause

Continue