rontolisp:wasm-import

(rontolisp:wasm-import 'name :from "module" :as "field" :params '(type...) :returns type)

Declares a function the WASM host provides (JavaScript in a browser, or another module preloaded into wasmtime) and makes it callable from Lisp under name exactly like a top-level defun — including #'name, funcall, mapcar and eval. It is a compile-time directive, not an ordinary function: on the interpreter and JVM backends it defines a stub that signals an error when called (there is no host to call), so the same source still loads on every backend. See Compiling to WebAssembly for the full guide and the WebGL galaxy example for a complete browser program.

Arguments

A quoted symbol naming the Lisp-visible function. It resolves in the current package like a defun name, so a directive after (in-package mylib) defines mylib:name.
:from — the import module name (the import-object key on the JavaScript side, or the --preload name in wasmtime). Defaults to "env".
:as — the import field name (the property inside that module object). Defaults to the bare Lisp name (without any package qualifier).
:params — a list of boundary type designators, one per parameter. Omitted, nil or '() means no arguments.
:returns — the result boundary type designator. Omitted, nil, '() or :void declares a void result (Lisp receives nil).

The type designators are shared with rontolisp:wasm-export:

Designator	WASM boundary	Notes
`:int`	`i32`	31-bit signed range (the internal `i31ref`)
`:float`	`f64`	an int or ratio argument is converted like the arithmetic built-ins
`:bool`	`i32`	`nil` crosses as `0`, anything else as `1`; a non-zero result reads back as `t`
`:string`	`(ptr, len)`	UTF-8 bytes in linear memory
`:s-expr`	`(ptr, len)`	the argument is printed to readable text; a result is parsed by the embedded reader

A :string result must be written into linear memory by the host (reserve the buffer with the exported __ronto_alloc) and returned as a (ptr, len) pair (a two-element array from JavaScript).

Limitations

Applies to the default (wasm-GC) Preview 1 core module only; --component and --no-gc reject the directive with an error. On the interpreter and JVM the declared name signals an error when called.
The directive must appear at top level, before use like a defun.
Instantiating the compiled module requires the host to provide every declared import; wasmtime run needs a --preload <module>=<file>.wasm for each import module name, and a JavaScript host passes an import object.
At most 7 parameters (the general WASM-backend arity limit).