Struct ExternalBuiltin 

pub struct ExternalBuiltin {
    pub seq_name: String,
    pub symbol: String,
    pub effect: Option<Effect>,
}

Definition of an external builtin function

External builtins are functions provided by a runtime extension (like an actor system) that should be callable from Seq code.

Type Safety

External builtins can optionally specify their stack effect for type checking. This affects how the type checker validates code using the builtin:

• With effect: The type checker enforces the declared signature. Use this when you know the exact stack effect (recommended).

• Without effect (None): The type checker assigns a maximally polymorphic signature ( ..a -- ..b ), meaning “accepts any stack, produces any stack”. This disables type checking for calls to this builtin - type errors involving this builtin will only be caught at runtime.

For best type safety, always provide an explicit effect when possible.

Fields

seq_name: String

The name used in Seq code (e.g., “journal-append”)

symbol: String

The symbol name for linking (e.g., “seq_actors_journal_append”)

Must contain only alphanumeric characters, underscores, and periods. This is validated at construction time to prevent LLVM IR injection.

effect: Option<Effect>

Optional stack effect for type checking.

• Some(effect): Type checker enforces this signature
• None: Type checker uses maximally polymorphic ( ..a -- ..b ), effectively disabling type checking for this builtin

Warning: Using None can hide type errors until runtime. Prefer providing an explicit effect when the signature is known.

Implementations

impl ExternalBuiltin

pub fn new(seq_name: impl Into<String>, symbol: impl Into<String>) -> Self

Create a new external builtin with just name and symbol

Panics

Panics if the symbol contains invalid characters for LLVM IR. Valid symbols contain only alphanumeric characters, underscores, and periods.

pub fn with_effect( seq_name: impl Into<String>, symbol: impl Into<String>, effect: Effect, ) -> Self

Create a new external builtin with a stack effect

Panics

Panics if the symbol contains invalid characters for LLVM IR.

Trait Implementations

impl Clone for ExternalBuiltin

fn clone(&self) -> ExternalBuiltin

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ExternalBuiltin

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.