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Embedding let-go in Go

let-go embeds cleanly as a scripting layer for Go programs. Define Go values and functions, hand them to the VM, run user-supplied Clojure against your data. Go structs roundtrip as records, Go channels are first-class let-go channels, and Go functions are callable from let-go.

import (
    "fmt"

    "github.com/nooga/let-go/pkg/api"
    "github.com/nooga/let-go/pkg/vm" // used in the sections below
)

c, _ := api.NewLetGo("myapp")

c.Def("x", 42)
c.Def("greet", func(name string) string {
    return "Hello, " + name
})

v, _ := c.Run(`(greet "world")`)
fmt.Println(v) // "Hello, world"

Structs roundtrip as records

Registered structs become records on the let-go side. Unmutated values unbox back to the original Go type for free; mutated ones go through vm.ToStruct[T].

type Item struct{ Name string; Price float64; Qty int }
vm.RegisterStruct[Item]("myapp/Item")

c.Def("item", Item{Name: "Widget", Price: 9.99, Qty: 5})
c.Run(`(:name item)`)                  // "Widget"
c.Run(`(* (:price item) (:qty item))`) // 49.95

Go channels are let-go channels

Go channels and vm.Chan plug into go / <! / >! directly:

inch := make(chan int)
outch := make(vm.Chan)
c.Def("in", inch)
c.Def("out", outch)

c.Run(`(go (loop [i (<! in)]
             (when i
               (>! out (inc i))
               (recur (<! in)))))`)

pkg/api/interop_test.go has the full set of embedding examples (defs, structs, channels, function calls).

Dropping net/http with lg_no_http

The http namespace is registered from an init(), so net/http — and crypto/tls and crypto/x509 behind it — is live in every binary that links pkg/rt, whether or not the embedded program ever opens a socket. The linker cannot see that it is unused.

Build with -tags lg_no_http to leave it out:

go build -tags lg_no_http ./cmd/lg-runtime

Measured on darwin/arm64 against cmd/lg-runtime:

build bytes
default 17,594,402
lg_no_http 12,175,106 −5,419,296 (−30.8%)
default, -s -w 12,131,874
lg_no_http, -s -w 8,382,754 −3,749,120 (−30.9%)

What changes in the tagged build: the http namespace is not installed, so http/get, http/serve and friends do not resolve; and io/reader on an io/url record returns an error instead of fetching. Everything else is untouched — file and resource slurp, io/reader on a path, and the rest of io behave the same.

TinyGo has never had a working http namespace (its net/http does not compile), so that lane already builds this way and gains nothing new from the tag. Both lanes now share one stub, pkg/rt/http_stub.go.