# Appendix B: Error codes > Appendix B: the AL error codes the Alice compiler reports, what each means, how to fix it, and where the book explains it. Canonical: https://alice-lang.org/documentation/learn/error-codes/ [Documentation index](https://alice-lang.org/documentation/llms.txt) ยท [Complete book](https://alice-lang.org/llms-full.txt) Every Alice compiler error has a code. The CLI prints it with the message, the location and a hint: ```text error[AL0202]: data race: spawned task writes captured variable 'total'; send it through a Channel or use an Actor --> main.al:2:20 | 2 | Par.For(100) { |i| total += i } | ^^^^^ = help: send the value through a Channel(T), use an Actor, or return it from the task ``` Messages and hints are available in English, Portuguese and Spanish: set `ALICE_LANG=pt` or pass `--lang es`. ## Language checks (AL01xx and AL02xx) | Code | Meaning | Typical fix | Chapter | | ------ | ------------------------------------------------------------------------------ | -------------------------------------------------------------- | ------------------------------------------------------------------ | | AL0101 | parse error: a missing `end`, an unexpected token | close the block, fix the token | [1.2](https://alice-lang.org/documentation/learn/first-program.md) | | AL0102 | an `end` without a block | remove it or fix the nesting | | | AL0103 | an unterminated string, character or interpolation | close it | | | AL0201 | a `case` misses enum variants | add the branches the message names | [7](https://alice-lang.org/documentation/learn/sum-types.md) | | AL0202 | a data race in concurrent code | `Atomic`, `Mutex(T)`, a channel, an actor, or return the value | [10](https://alice-lang.org/documentation/learn/safety.md) | | AL0203 | assignment to a `val` | use a plain variable | [3](https://alice-lang.org/documentation/learn/common-concepts.md) | | AL0204 | the type cannot be inferred from `nil` | write `x : Type? = nil` | [3](https://alice-lang.org/documentation/learn/common-concepts.md) | | AL0205 | a type is required, as for a constant collection or a `getter` without a value | add `: Type` | [5](https://alice-lang.org/documentation/learn/strings.md) | | AL0206 | `yield` in a method without a block | declare a block parameter | | | AL0207 | an owned array escapes | keep it local, or drop `own` | [9](https://alice-lang.org/documentation/learn/ownership.md) | | AL0208 | use after move | reassign, or read through the new owner | [9](https://alice-lang.org/documentation/learn/ownership.md) | | AL0209 | `par for` iterations are not provably independent | remove the dependency, or use `for` or `prefix_sum` | [11](https://alice-lang.org/documentation/learn/parallelism.md) | | AL0210 | a `pure def` or `rule` has an effect | remove the effect, or drop `pure` | [10](https://alice-lang.org/documentation/learn/safety.md) | | AL0211 | `par a, b = ...` cannot fork | make both calls pure and independent | [11](https://alice-lang.org/documentation/learn/parallelism.md) | | AL0212 | a `safe def` reaches ambient authority | pass in what it needs | [10](https://alice-lang.org/documentation/learn/safety.md) | | AL0213 | a `borrow` parameter escapes | only read and lend it, or take it with `own` | [9](https://alice-lang.org/documentation/learn/ownership.md) | | AL0214 | a rule's domain has more than 2^32 cases | narrow it, split it, or use `alice prove --smt` | [13](https://alice-lang.org/documentation/learn/proofs.md) | | AL0215 | a native callback captures variables | pass state through the C API's user data | [17](https://alice-lang.org/documentation/learn/native.md) | | AL0216 | a pointer operation outside `unsafe` | wrap it in `unsafe ... end` | [17](https://alice-lang.org/documentation/learn/native.md) | | AL0217 | one array passed as two parameters, one of them written | pass a copy | [9](https://alice-lang.org/documentation/learn/ownership.md) | | AL0218 | a `@[Stack]` value captured or stored on the heap | pass the fields it needs | [9](https://alice-lang.org/documentation/learn/ownership.md) | | AL0219 | a value used after it was sent to another thread | send a copy | [10](https://alice-lang.org/documentation/learn/safety.md) | | AL0220 | strict mode: an expression has no static type | annotate, call a typed method, or write `Any` | [10](https://alice-lang.org/documentation/learn/safety.md) | | AL0221 | a field that no `initialize` assigns | assign it, give a default, or make it nilable | [6](https://alice-lang.org/documentation/learn/types.md) | | AL0230 | an actor message type is not sendable | send immutable values: numbers, strings, records, tuples | [15](https://alice-lang.org/documentation/learn/async.md) | | AL0231 | an actor captures mutable outside state | build the state in `init` | [15](https://alice-lang.org/documentation/learn/async.md) | | AL0001 | another compiler error | read the message | | Codes from AL0222 to AL0229 are reserved for features designed for 1.0 ([Appendix E](https://alice-lang.org/documentation/learn/coming-in-1-0.md)) and are not reported yet. ## Type-checking errors (AL03xx) Alice type-checks the generated code with the .NET compiler and reports its errors in Alice terms, with Alice type names: | Code | Meaning | Example message | | ------ | -------------------------------------------- | ----------------------------------------------------------- | | AL0301 | an operator is not defined for these types | `'+' is not defined for Bool and Int32` | | AL0302 | no such method | `undefined method 'open' for Box` | | AL0303 | unknown name | `undefined name 'totl'` | | AL0304 | type mismatch | `type mismatch: expected Int32, got String` | | AL0305 | wrong argument type | `argument 1 of greet: expected String, got Int32` | | AL0306 | wrong number of arguments | `wrong number of arguments for f (given 2)` | | AL0307 | unknown type | `unknown type 'Foo' (missing require, using or a package?)` | | AL0308 | not every path returns a value | | | AL0309 | a variable may be used before it is assigned | | | AL0310 | a value may be `nil` here | `value may be nil here; check it ...` | | AL0311 | ambiguous call | | | AL0312 | generic type arguments cannot be inferred | `cannot infer type arguments for 'f'` | | AL0313 | a private member used from outside | `'x' is private here` | | AL0314 | a read-only member assigned | `'x' is read-only` | | AL0315 | an instance member used without an instance | | | AL0300 | any other type-checking error | the .NET message with Alice type names | ## Editor and command-line errors `AL0401` is reported by the language server when an open `alice.toml` or `.alproj` does not parse. Command-line usage mistakes print `error:` with a `hint:` line and exit with status 2; internal failures exit with 70. The [diagnostics reference](https://alice-lang.org/documentation/reference/diagnostics.md) has the full table with more examples. ## Continue reading - Previous: [Appendix A: Keywords and operators](https://alice-lang.org/documentation/learn/keywords.md) - Next: [Appendix C: Coming from Ruby, Crystal or C#](https://alice-lang.org/documentation/learn/from-ruby.md)