Add sys: module to expose platform and arch vars

Resolves #916

pkg/eval/os/os.go

@@ -0,0 +1,29 @@
+// Package `os` exposes variables and functions that deal with the specific
+// platform being run on; such as the OS name and CPU architecture.
+package os
+
+import (
+	"runtime"
+
+	"github.com/elves/elvish/pkg/eval"
+	"github.com/elves/elvish/pkg/eval/vars"
+)
+
+//elvdoc:var arch
+//
+// The architecture of the platform; e.g., amd64, arm, ppc.
+// This corresponds to Go's
+// [`GOARCH`](https://pkg.go.dev/runtime?tab=doc#pkg-constants) constant.
+// This is read-only.
+
+//elvdoc:var platform
+//
+// The name of the platform; e.g., darwin (macOS), linux, etc.
+// This corresponds to Go's
+// [`GOOS`](https://pkg.go.dev/runtime?tab=doc#pkg-constants) constant.
+// This is read-only.
+
+var Ns = eval.Ns{
+	"arch": vars.NewReadOnly(runtime.GOARCH),
+	"platform": vars.NewReadOnly(runtime.GOOS),
+}

pkg/eval/os/os_test.go

@@ -0,0 +1,18 @@
+package os
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/elves/elvish/pkg/eval"
+)
+
+var That = eval.That
+
+func TestOs(t *testing.T) {
+	setup := func(ev *eval.Evaler) { ev.Builtin.AddNs("os", Ns) }
+	eval.TestWithSetup(t, setup,
+		That(`put $os:arch`).Puts(runtime.GOARCH),
+		That(`put $os:platform`).Puts(runtime.GOOS),
+	)
+}

pkg/program/shell/runtime.go

@@ -15,6 +15,7 @@ import (
 	"github.com/elves/elvish/pkg/eval/re"
 	"github.com/elves/elvish/pkg/eval/store"
 	"github.com/elves/elvish/pkg/eval/str"
+	elvish_os "github.com/elves/elvish/pkg/eval/os"
 	daemonp "github.com/elves/elvish/pkg/program/daemon"
 )
 
@@ -74,6 +75,7 @@ func InitRuntime(binpath, sockpath, dbpath string) (*eval.Evaler, string) {
 	ev.InstallModule("math", eval.MathNs)
 	ev.InstallModule("re", re.Ns)
 	ev.InstallModule("str", str.Ns)
+	ev.InstallModule("os", elvish_os.Ns)
 	if sockpath != "" && dbpath != "" {
 		spawner := &daemonp.Daemon{
 			BinPath:       binpath,

website/ref/index.toml

@@ -10,6 +10,10 @@ title = "The Builtin Module"
 name = "edit"
 title = "The Editor Module (edit:)"
 
+[[articles]]
+name = "os"
+title = "The Operating System Module (os:)"
+
 [[articles]]
 name = "re"
 title = "The Regular Expression Module (re:)"

website/ref/os.md

@@ -0,0 +1,10 @@
+<!-- toc -->
+
+# Introduction
+
+The `os:` module provides platform specific constants.
+
+Function usages are given in the same format as in the
+reference doc for the [builtin module](builtin.html).
+
+@elvdoc -ns os: -dir ../pkg/eval/os