From cc412f86846ee94d66ad2954cb30e9d1296d07a9 Mon Sep 17 00:00:00 2001
From: Qi Xiao <xiaqqaix@gmail.com>
Date: Thu, 18 Feb 2016 19:30:08 +0100
Subject: [PATCH] Syncing from $env:PATH to $paths and ev.searchPaths.

This addresses #139.
---
 eval/eval.go     | 24 +++++++++++++++---------
 eval/pathList.go | 41 +++++++++++++++++++++++++++++++++++++++++
 eval/value.go    | 34 +++++++++++++++++++++++++---------
 eval/variable.go | 13 +++++++++++++
 4 files changed, 94 insertions(+), 18 deletions(-)
 create mode 100644 eval/pathList.go

diff --git a/eval/eval.go b/eval/eval.go
index d540a1b6..58528bea 100644
--- a/eval/eval.go
+++ b/eval/eval.go
@@ -54,22 +54,24 @@ func NewEvaler(st *store.Store) *Evaler {
 		searchPaths = []string{"/bin"}
 	}
 
+	ev := &Evaler{nil, map[string]Namespace{}, searchPaths, st}
+
 	// Construct initial global namespace
 	pid := String(strconv.Itoa(syscall.Getpid()))
 	paths := NewList()
 	paths.appendStrings(searchPaths)
-	global := Namespace{
-		"pid":   NewPtrVariable(pid),
-		"ok":    NewPtrVariable(OK),
-		"true":  NewPtrVariable(Bool(true)),
-		"false": NewPtrVariable(Bool(false)),
-		"paths": NewPtrVariable(paths),
+	ev.global = Namespace{
+		"pid":   NewRoVariable(pid),
+		"ok":    NewRoVariable(OK),
+		"true":  NewRoVariable(Bool(true)),
+		"false": NewRoVariable(Bool(false)),
+		"paths": NewRoVariable(PathList{&ev.searchPaths}),
 	}
 	for _, b := range builtinFns {
-		global[FnPrefix+b.Name] = NewPtrVariable(b)
+		ev.global[FnPrefix+b.Name] = NewRoVariable(b)
 	}
 
-	return &Evaler{global, map[string]Namespace{}, searchPaths, st}
+	return ev
 }
 
 func (e *Evaler) AddModule(name string, ns Namespace) {
@@ -263,7 +265,11 @@ func (ev *Evaler) Global() map[string]Variable {
 // returned.
 func (ec *EvalCtx) ResolveVar(ns, name string) Variable {
 	if ns == "env" {
-		return newEnvVariable(name)
+		ev := envVariable{name}
+		if name == "PATH" {
+			return pathEnvVariable{ev, &ec.searchPaths}
+		}
+		return ev
 	}
 	if mod, ok := ec.modules[ns]; ok {
 		return mod[name]
diff --git a/eval/pathList.go b/eval/pathList.go
new file mode 100644
index 00000000..d17f46d5
--- /dev/null
+++ b/eval/pathList.go
@@ -0,0 +1,41 @@
+package eval
+
+import (
+	"errors"
+
+	"github.com/elves/elvish/parse"
+)
+
+// PathList wraps a list of search paths into a readonly list-like Value.
+type PathList struct {
+	inner *[]string
+}
+
+func (l PathList) Kind() string {
+	return "list"
+}
+
+func (l PathList) Repr() string {
+	var b ListReprBuilder
+	for _, v := range *l.inner {
+		b.WriteElem(parse.Quote(v))
+	}
+	return b.String()
+}
+
+func (l PathList) IndexOne(idx Value) Value {
+	// XXX copied from index.go
+	i := intIndex(idx)
+
+	if i < 0 {
+		i += len(*l.inner)
+	}
+	if i < 0 || i >= len(*l.inner) {
+		throw(ErrIndexOutOfRange)
+	}
+	return String((*l.inner)[i])
+}
+
+func (l PathList) IndexSet(idx, v Value) {
+	throw(errors.New("assignment to $paths not implemented; assign to $env:PATH instead"))
+}
diff --git a/eval/value.go b/eval/value.go
index 9d53dfb5..2c62bf43 100644
--- a/eval/value.go
+++ b/eval/value.go
@@ -190,16 +190,32 @@ func (l List) appendStrings(ss []string) {
 }
 
 func (l List) Repr() string {
-	buf := new(bytes.Buffer)
-	buf.WriteRune('[')
-	for i, v := range *l.inner {
-		if i > 0 {
-			buf.WriteByte(' ')
-		}
-		buf.WriteString(v.Repr())
+	var b ListReprBuilder
+	for _, v := range *l.inner {
+		b.WriteElem(v.Repr())
 	}
-	buf.WriteRune(']')
-	return buf.String()
+	return b.String()
+}
+
+type ListReprBuilder struct {
+	buf bytes.Buffer
+}
+
+func (b *ListReprBuilder) WriteElem(v string) {
+	if b.buf.Len() == 0 {
+		b.buf.WriteByte('[')
+	} else {
+		b.buf.WriteByte(' ')
+	}
+	b.buf.WriteString(v)
+}
+
+func (b *ListReprBuilder) String() string {
+	if b.buf.Len() == 0 {
+		return "["
+	}
+	b.buf.WriteByte(']')
+	return b.buf.String()
 }
 
 // Map is a map from string to Value.
diff --git a/eval/variable.go b/eval/variable.go
index 08088e3b..5b3f7998 100644
--- a/eval/variable.go
+++ b/eval/variable.go
@@ -3,6 +3,7 @@ package eval
 import (
 	"errors"
 	"os"
+	"strings"
 )
 
 var (
@@ -76,3 +77,15 @@ func (ev envVariable) Set(val Value) {
 func (ev envVariable) Get() Value {
 	return String(os.Getenv(ev.name))
 }
+
+type pathEnvVariable struct {
+	envVariable
+	ppaths *[]string
+}
+
+func (pev pathEnvVariable) Set(val Value) {
+	s := ToString(val)
+	os.Setenv(pev.name, s)
+	paths := strings.Split(s, ":")
+	*pev.ppaths = paths
+}