Compile errors

The compiler emits diagnostics with a stable Exxx code identifying the phase and the specific check. The first digit is the phase: 0 lexer, 1 parser, 2 name resolution, 3 type checking, 4 verifier. Every diagnostic carries a source location and a human-readable message. The list below covers the common ones and what they usually mean.

Lexer (E0xx)#

These fire before any structure is recognized — the source isn't even tokens yet.

Code	Symptom	Common cause
`E001`	Unexpected character	A stray byte the lexer doesn't recognize. Check for smart-quotes pasted from a doc.
`E002`	Unterminated string	A `"` without a matching close. Multi-line strings need explicit escapes.
`E003`	Unterminated comment	A `/` without a closing `/`.
`E004`	Invalid escape sequence	An unknown `\x` inside a string literal.
`E005`	Invalid numeric literal	Trailing alpha after digits, or a number that doesn't parse.
`E006`	Reserved keyword	A reserved word used as an identifier. Rename the binding.
`E007`	Unknown `@`-keyword	An `@something` the compiler doesn't recognize. Check the spelling against the language dictionary.
`E008`	Unterminated string interpolation	`${` without a matching `}` inside a string.

Parser (E1xx)#

The token stream didn't match the grammar.

Code	Symptom	Common cause
`E100`	Unexpected token	A token where the grammar expected something else — often a stray `,` or missing `=`.
`E101`	Expected specific token	The grammar required a particular token (e.g. `}`) and got something else.
`E102`	Expected expression	A spot that needs an expression got a statement or punctuation.
`E103`	Expected type	A type annotation slot got a non-type.
`E104`	Expected block	A `{ … }` block was expected (often after `@flow` or `@rigid`).
`E105`	Expected identifier	A name was expected (parameter, field, etc.).
`E106`	Invalid pattern	A `@match` arm has an unrecognized pattern shape.
`E107`	Expected core declaration	The file's first top-level construct must be `@core`.
`E108`	Duplicate field	A struct or block has the same field name twice.

Name resolution (E2xx)#

The grammar parsed, but a reference points to something that isn't defined.

Code	Symptom	Common cause
`E200`	Undefined name	A variable is referenced before it's bound.
`E201`	Duplicate name	Two declarations of the same name at the same scope.
`E202`	Undefined type	A type annotation references a type that doesn't exist. Check spelling and that the `type` declaration came first.
`E203`	Unresolved import	An `import` couldn't locate its target.
`E204`	Undefined flow	A `@core_call` or call references a flow that isn't declared.
`E205`	Undefined plugin	A plugin call references a plugin not declared in `@plugins`.
`E206`	Undefined model	A `@flexible` or `@model_call` references an LLM role not declared in `@llm`.

Type checking (E3xx)#

Names resolved but types don't line up.

Code	Symptom	Common cause
`E300`	Type mismatch	A value's inferred type doesn't match the expected type at its use site.
`E301`	Incompatible operands	An operator was applied to operands of incompatible types (`"x" + 1`, etc.).
`E302`	Wrong argument count	A call has too many or too few arguments.
`E303`	Wrong argument type	A call's argument doesn't match the parameter's declared type.
`E304`	Missing return	A flow declared to return a value has a path that doesn't return.
`E305`	Void return value	A flow declared `void` returns a value.
`E306`	Memory type mismatch	A `memory.<key> = value` writes a type the schema doesn't allow.
`E307`	Forbidden `Any` type	An `Any` type leaked into a position where a specific type is required.

Verifier (E4xx)#

Types pass but the program violates a runtime invariant that's checkable statically.

Code	Symptom	Common cause
`E400`	Rigid non-determinism	A `@rigid` block contains a non-deterministic operation. Rigid blocks must be replayable.
`E401`	Internal flow reachable	An `@internal` flow is reachable from a public surface. Mark it `pub` or restructure callers.
`E402`	Entity key missing	An `entity`-instance Core declares `entity_key` but never produces it.
`E403`	Checkpoint inside `@parallel`	A `@checkpoint` is nested inside a `@parallel` branch. Suspend/resume across parallel branches isn't supported.
`E404`	Emit schema mismatch	An `emit` event's payload doesn't match the declared event schema in the manifest.
`E405`	LLM call inside `@rigid`	A `@flexible` or `@model_call` is nested inside a `@rigid` block. LLM calls aren't allowed in rigid context.

Tips#

Pass --strict to scaicore check and scaicore compile to elevate warnings to errors. Useful in CI.
A diagnostic's source location pinpoints the immediate cause; if it's confusing, scan one or two declarations earlier — a missing comma or brace cascades into several downstream complaints.
For verifier errors specifically, the message often suggests the structural change (e.g. "move the @checkpoint outside the @parallel block"). Read the full message before refactoring.