Diagnostic Codes

Diagnostic codes are stable identifiers for tooling, tests, and educational explanations. The message adds context, but code-based handling should use the code. Codes are grouped by failure layer; a missing number is reserved and has no current meaning.

Syntax And Parsing (NLK1xxx)

| Code | Meaning | | --------- | ---------------------------------------------------------------------------------------------------- | | NLK1001 | Invalid token or character. | | NLK1002 | Invalid indentation, including tabs or an unmatched dedent. | | NLK1003 | Unterminated string, block comment, delimiter, or other construct. | | NLK1004 | Required token or syntactic form is missing. | | NLK1005 | Recognized but unsupported syntax, such as a slice step, comparison chain, or unknown string escape. | | NLK1006 | The implementation’s structural syntax-nesting limit was exceeded. |

Names, Structure, Types, And Effects (NLK2xxx)

| Code | Meaning | | --------- | -------------------------------------------------------------------------------- | | NLK2001 | A variable is not defined on the current path. | | NLK2002 | A called function is not available at that source position. | | NLK2003 | Duplicate value, function, parameter, or related declaration. | | NLK2004 | A reserved built-in name was rebound. | | NLK2005 | Invalid function structure, such as a misplaced or non-final return. | | NLK2006 | Statement is illegal in this scope or placement. | | NLK2007 | Call arity or named-argument binding does not match the signature. | | NLK2008 | Type annotation is unknown, malformed, or invalid for that position. | | NLK2009 | A recoverable error could flow directly into a context that requires success. | | NLK2010 | try or catch is invalid for the operand’s error effect. | | NLK2011 | A value does not satisfy an annotated parameter, assignment, or return contract. | | NLK2013 | Code attempts to compare an error value. | | NLK2014 | A recursive container operation cannot prove its required safety constraint. |

Commit Loops (NLK3xxx)

| Code | Meaning | | --------- | ------------------------------------------------------------------------------------ | | NLK3001 | init is not paired with a legal commit loop. | | NLK3002 | Primed assignment is illegal in this position. | | NLK3003 | Primed state is read where next-state reads are forbidden. | | NLK3004 | A primed name uses the wrong prime depth for the current loop. | | NLK3005 | The same primed target is assigned more than once in a round. | | NLK3006 | A commit-loop guard is statically constant. | | NLK3007 | A nested commit loop is placed where its parent state cannot be materialized safely. | | NLK3008 | Commit-loop state is updated directly instead of through the next-state layer. | | NLK3009 | A while commit loop is missing its required adjacent init block. | | NLK3010 | A pragma is unknown or placed outside its legal loop position. | | NLK3011 | rhs_prime uses an unknown guarantee name. | | NLK3012 | Primed read dependencies form a cycle and cannot be scheduled. |

Runtime Values (NLK4xxx)

| Code | Meaning | | --------- | ---------------------------------------------------------------------------- | | NLK4001 | Runtime type error. | | NLK4002 | Value is of the right broad type but outside an operation’s valid domain. | | NLK4003 | A requested dict key or set element is absent. | | NLK4004 | A sequence index is out of range. | | NLK4005 | A sparse next-state container location is updated more than once in a round. | | NLK4006 | An unhandled error value reached a context that cannot consume errors. |

NLK4002, NLK4003, and NLK4004 become recoverable err values only for operations explicitly registered as safe value-level operations. Examples include list.get, one-argument dict.get, list.pop, list.index, set.remove, num, ord, and chr. Raw indexing and type/arity failures remain fatal. Handle a registered failure with catch, propagate it from an error-capable function with prefix try, or retain it in an explicitly error-capable annotation.

Resource And Internal Failures (NLK5xxx)

| Code | Meaning | | --------- | ------------------------------------------------------------------------------- | | NLK5001 | Configured global commit-loop round limit exceeded. | | NLK5002 | Runtime nested-loop depth limit exceeded. | | NLK5003 | Configured source prime-depth limit exceeded. | | NLK5005 | Function call-depth limit exceeded. | | NLK5006 | Runtime value size, nesting, repetition, or allocation limit exceeded. | | NLK5999 | Interpreter invariant failed; this normally indicates an implementation defect. |

All NLK1xxx, NLK2xxx, NLK3xxx, NLK5xxx, NLK4001, NLK4005, and NLK4006 diagnostics are fatal. Fatal means the current run does not produce a normal program result and the CLI exits with status 1.