Using Go

Use any Go package from OSL with a go: import, pass values both ways, and read the Go that OSL generates.

OSL compiles to Go, so the whole Go ecosystem is part of OSL's. Import any Go package with go: in front of its path, and call it as you would in Go. There are no bindings to write.

import "go:strings"
import "go:unicode"

log strings.ToUpper("quiet")
log strings.Count("banana", "a")
log strings.Fields(" spread   out  words ")
log unicode.IsDigit(55)

Refer to the package by its Go name, usually the last part of its path: go:net/http is http, go:path/filepath is filepath.

Values cross over#

OSL values convert to the Go types a function expects, and Go results come back as OSL values. Strings stay strings, numbers convert to the right Go number type, and arrays become Go slices, array literals included:

import "go:strings"
import "go:slices"
import "go:math"

def largest(int[] values) int -> slices.Max(values)

log strings.Join(["a", "b", "c"], "-")
log largest([3, 9, 4])
log math.Hypot(3, 4)

Go types#

Go types work as OSL types, for variables, parameters and return values. Read and set exported fields directly; lowercase field names map to Go's exported ones:

import "go:image"

image.Point p = image.Pt(1, 2)
p.X = 5
log p.X p.Y

image.Point q = image.Point(x = 10, y = 20)
log q.Add(p).String()

A Go function's result keeps its Go type, so you can call its methods straight away, as q.Add(p).String() does.

Pointers to Go types are written with *, as in *strings.Builder.

Modules from outside the standard library#

Packages beyond Go's standard library come from Go modules. Add them to your project with Opal, which records them in go.mod:

opal add go:github.com/google/uuid

import "go:github.com/google/uuid"

log uuid.NewString()

Reading the generated Go#

osl transpile file.osl prints the Go that OSL generates. Every example on this site has a Go button that shows it. It's a good way to see what your code costs: typed OSL becomes plain, direct Go.

osl transpile main.osl

string csv = "pear,fig,apple"

log csv

string csv = "pear,fig,apple"

log csv

PEAR | FIG | APPLE