exp/template: add template sets, allowing templates to reference one another

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4673042

7 files changed, 626 insertions, 116 deletions

diff --git a/src/pkg/exp/template/Makefile b/src/pkg/exp/template/Makefile
index a2d39e248a..50a0bd7234 100644
--- a/src/pkg/exp/template/Makefile
+++ b/src/pkg/exp/template/Makefile
@@ -9,5 +9,6 @@ GOFILES=\
 	exec.go\
 	lex.go\
 	parse.go\
+	set.go\
 
 include ../../../Make.pkg
diff --git a/src/pkg/exp/template/exec.go b/src/pkg/exp/template/exec.go
index 27c1b096ec..3eaecd1941 100644
--- a/src/pkg/exp/template/exec.go
+++ b/src/pkg/exp/template/exec.go
@@ -9,6 +9,7 @@ import (
 	"io"
 	"os"
 	"reflect"
+	"strings"
 )
 
 // state represents the state of an execution. It's not part of the
@@ -17,6 +18,7 @@ import (
 type state struct {
 	tmpl *Template
 	wr   io.Writer
+	set  *Set
 	line int // line number for errors
 }
 
@@ -33,11 +35,19 @@ func (s *state) error(err os.Error) {
 
 // Execute applies a parsed template to the specified data object,
 // writing the output to wr.
-func (t *Template) Execute(wr io.Writer, data interface{}) (err os.Error) {
+func (t *Template) Execute(wr io.Writer, data interface{}) os.Error {
+	return t.ExecuteInSet(wr, data, nil)
+}
+
+// ExecuteInSet applies a parsed template to the specified data object,
+// writing the output to wr. Nested template invocations will be resolved
+// from the specified set.
+func (t *Template) ExecuteInSet(wr io.Writer, data interface{}, set *Set) (err os.Error) {
 	defer t.recover(&err)
 	state := &state{
 		tmpl: t,
 		wr:   wr,
+		set:  set,
 		line: 1,
 	}
 	if t.root == nil {
@@ -49,7 +59,6 @@ func (t *Template) Execute(wr io.Writer, data interface{}) (err os.Error) {
 
 // Walk functions step through the major pieces of the template structure,
 // generating output as they go.
-
 func (s *state) walk(data reflect.Value, n node) {
 	switch n := n.(type) {
 	case *actionNode:
@@ -59,17 +68,56 @@ func (s *state) walk(data reflect.Value, n node) {
 		for _, node := range n.nodes {
 			s.walk(data, node)
 		}
+	case *ifNode:
+		s.walkIfOrWith(nodeIf, data, n.pipeline, n.list, n.elseList)
 	case *rangeNode:
 		s.walkRange(data, n)
 	case *textNode:
 		if _, err := s.wr.Write(n.text); err != nil {
 			s.error(err)
 		}
+	case *templateNode:
+		s.walkTemplate(data, n)
+	case *withNode:
+		s.walkIfOrWith(nodeWith, data, n.pipeline, n.list, n.elseList)
 	default:
 		s.errorf("unknown node: %s", n)
 	}
 }
 
+// walkIfOrWith walks an 'if' or 'with' node. The two control structures
+// are identical in behavior except that 'with' sets dot.
+func (s *state) walkIfOrWith(typ nodeType, data reflect.Value, pipe []*commandNode, list, elseList *listNode) {
+	val := s.evalPipeline(data, pipe)
+	truth := false
+	switch val.Kind() {
+	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
+		truth = val.Len() > 0
+	case reflect.Bool:
+		truth = val.Bool()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		truth = val.Int() != 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		truth = val.Uint() != 0
+	case reflect.Float32, reflect.Float64:
+		truth = val.Float() != 0
+	case reflect.Complex64, reflect.Complex128:
+		truth = val.Complex() != 0
+	case reflect.Chan, reflect.Func, reflect.Ptr:
+		truth = !val.IsNil()
+	default:
+		s.errorf("if/with can't use value of type %T", val.Interface())
+	}
+	if truth {
+		if typ == nodeWith {
+			data = val
+		}
+		s.walk(data, list)
+	} else if elseList != nil {
+		s.walk(data, elseList)
+	}
+}
+
 func (s *state) walkRange(data reflect.Value, r *rangeNode) {
 	val := s.evalPipeline(data, r.pipeline)
 	switch val.Kind() {
@@ -97,6 +145,21 @@ func (s *state) walkRange(data reflect.Value, r *rangeNode) {
 	}
 }
 
+func (s *state) walkTemplate(data reflect.Value, t *templateNode) {
+	name := s.evalArg(data, reflect.TypeOf("string"), t.name).String()
+	if s.set == nil {
+		s.errorf("no set defined in which to invoke template named %q", name)
+	}
+	tmpl := s.set.tmpl[name]
+	if tmpl == nil {
+		s.errorf("template %q not in set", name)
+	}
+	data = s.evalPipeline(data, t.pipeline)
+	newState := *s
+	newState.tmpl = tmpl
+	newState.walk(data, tmpl.root)
+}
+
 // Eval functions evaluate pipelines, commands, and their elements and extract
 // values from the data structure by examining fields, calling methods, and so on.
 // The printing of those values happens only through walk functions.
@@ -110,16 +173,38 @@ func (s *state) evalPipeline(data reflect.Value, pipe []*commandNode) reflect.Va
 }
 
 func (s *state) evalCommand(data reflect.Value, cmd *commandNode, final reflect.Value) reflect.Value {
-	switch field := cmd.args[0].(type) {
+	firstWord := cmd.args[0]
+	if field, ok := firstWord.(*fieldNode); ok {
+		return s.evalFieldNode(data, field, cmd.args, final)
+	}
+	if len(cmd.args) > 1 || final.IsValid() {
+		// TODO: functions
+		s.errorf("can't give argument to non-method %s", cmd.args[0])
+	}
+	switch word := cmd.args[0].(type) {
 	case *dotNode:
-		if final.IsValid() {
-			s.errorf("can't give argument to dot")
-		}
 		return data
-	case *fieldNode:
-		return s.evalFieldNode(data, field, cmd.args, final)
+	case *boolNode:
+		return reflect.ValueOf(word.true)
+	case *numberNode:
+		// These are ideal constants but we don't know the type
+		// and we have no context.  (If it was a method argument,
+		// we'd know what we need.) The syntax guides us to some extent.
+		switch {
+		case word.isComplex:
+			return reflect.ValueOf(word.complex128) // incontrovertible.
+		case word.isFloat && strings.IndexAny(word.text, ".eE") >= 0:
+			return reflect.ValueOf(word.float64)
+		case word.isInt:
+			return reflect.ValueOf(word.int64)
+		case word.isUint:
+			return reflect.ValueOf(word.uint64)
+		}
+	case *stringNode:
+		return reflect.ValueOf(word.text)
+	default:
+		s.errorf("can't handle command %q", firstWord)
 	}
-	s.errorf("%s not a field", cmd.args[0])
 	panic("not reached")
 }
 
@@ -148,7 +233,7 @@ func (s *state) evalField(data reflect.Value, fieldName string) reflect.Value {
 		}
 		s.errorf("%s has no field %s", data.Type(), fieldName)
 	default:
-		s.errorf("can't evaluate field %s of  type %s", fieldName, data.Type())
+		s.errorf("can't evaluate field %s of type %s", fieldName, data.Type())
 	}
 	panic("not reached")
 }
@@ -282,7 +367,7 @@ func (s *state) evalUnsignedInteger(v reflect.Value, typ reflect.Type, n node) r
 }
 
 func (s *state) evalFloat(v reflect.Value, typ reflect.Type, n node) reflect.Value {
-	if n, ok := n.(*numberNode); ok && n.isFloat && !n.imaginary {
+	if n, ok := n.(*numberNode); ok && n.isFloat {
 		value := reflect.New(typ).Elem()
 		value.SetFloat(n.float64)
 		return value
@@ -292,9 +377,9 @@ func (s *state) evalFloat(v reflect.Value, typ reflect.Type, n node) reflect.Val
 }
 
 func (s *state) evalComplex(v reflect.Value, typ reflect.Type, n node) reflect.Value {
-	if n, ok := n.(*numberNode); ok && n.isFloat && n.imaginary {
+	if n, ok := n.(*numberNode); ok && n.isComplex {
 		value := reflect.New(typ).Elem()
-		value.SetComplex(complex(0, n.float64))
+		value.SetComplex(n.complex128)
 		return value
 	}
 	s.errorf("expected complex; found %s", n)
diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go
index bd21125ef4..6e4da692e9 100644
--- a/src/pkg/exp/template/exec_test.go
+++ b/src/pkg/exp/template/exec_test.go
@@ -16,17 +16,20 @@ import (
 // T has lots of interesting pieces to use to test execution.
 type T struct {
 	// Basics
-	I   int
-	U16 uint16
-	X   string
+	I           int
+	U16         uint16
+	X           string
+	FloatZero   float64
+	ComplexZero float64
 	// Nested structs.
 	U *U
 	// Slices
-	SI     []int
-	SEmpty []int
-	SB     []bool
+	SI      []int
+	SIEmpty []int
+	SB      []bool
 	// Maps
 	MSI      map[string]int
+	MSIone   map[string]int // one element, for deterministic output
 	MSIEmpty map[string]int
 }
 
@@ -76,13 +79,14 @@ type U struct {
 }
 
 var tVal = &T{
-	I:   17,
-	U16: 16,
-	X:   "x",
-	U:   &U{"v"},
-	SI:  []int{3, 4, 5},
-	SB:  []bool{true, false},
-	MSI: map[string]int{"one": 1, "two": 2, "three": 3},
+	I:      17,
+	U16:    16,
+	X:      "x",
+	U:      &U{"v"},
+	SI:     []int{3, 4, 5},
+	SB:     []bool{true, false},
+	MSI:    map[string]int{"one": 1, "two": 2, "three": 3},
+	MSIone: map[string]int{"one": 1},
 }
 
 type execTest struct {
@@ -94,31 +98,80 @@ type execTest struct {
 }
 
 var execTests = []execTest{
+	// Trivial cases.
 	{"empty", "", "", nil, true},
 	{"text", "some text", "some text", nil, true},
+	// Fields of structs.
 	{".X", "-{{.X}}-", "-x-", tVal, true},
 	{".U.V", "-{{.U.V}}-", "-v-", tVal, true},
+	// Dots of all kinds to test basic evaluation.
+	{"dot int", "<{{.}}>", "<13>", 13, true},
+	{"dot uint", "<{{.}}>", "<14>", uint(14), true},
+	{"dot float", "<{{.}}>", "<15.1>", 15.1, true},
+	{"dot bool", "<{{.}}>", "<true>", true, true},
+	{"dot complex", "<{{.}}>", "<(16.2-17i)>", 16.2 - 17i, true},
+	{"dot string", "<{{.}}>", "<hello>", "hello", true},
+	{"dot slice", "<{{.}}>", "<[-1 -2 -3]>", []int{-1, -2, -3}, true},
+	{"dot map", "<{{.}}>", "<map[two:22 one:11]>", map[string]int{"one": 11, "two": 22}, true},
+	{"dot struct", "<{{.}}>", "<{7 seven}>", struct {
+		a int
+		b string
+	}{7, "seven"}, true},
+	// Method calls.
 	{".Method0", "-{{.Method0}}-", "-resultOfMethod0-", tVal, true},
 	{".Method1(1234)", "-{{.Method1 1234}}-", "-1234-", tVal, true},
 	{".Method1(.I)", "-{{.Method1 .I}}-", "-17-", tVal, true},
 	{".Method2(3, .X)", "-{{.Method2 3 .X}}-", "-Method2: 3 x-", tVal, true},
 	{".Method2(.U16, `str`)", "-{{.Method2 .U16 `str`}}-", "-Method2: 16 str-", tVal, true},
+	// Pipelines.
 	{"pipeline", "-{{.Method0 | .Method2 .U16}}-", "-Method2: 16 resultOfMethod0-", tVal, true},
+	// If.
+	{"if true", "{{if true}}TRUE{{end}}", "TRUE", tVal, true},
+	{"if false", "{{if false}}TRUE{{else}}FALSE{{end}}", "FALSE", tVal, true},
+	{"if 1", "{{if 1}}NON-ZERO{{else}}ZERO{{end}}", "NON-ZERO", tVal, true},
+	{"if 0", "{{if 0}}NON-ZERO{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"if 1.5", "{{if 1.5}}NON-ZERO{{else}}ZERO{{end}}", "NON-ZERO", tVal, true},
+	{"if 0.0", "{{if .FloatZero}}NON-ZERO{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"if 1.5i", "{{if 1.5i}}NON-ZERO{{else}}ZERO{{end}}", "NON-ZERO", tVal, true},
+	{"if 0.0i", "{{if .ComplexZero}}NON-ZERO{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"if emptystring", "{{if ``}}NON-EMPTY{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"if string", "{{if `notempty`}}NON-EMPTY{{else}}EMPTY{{end}}", "NON-EMPTY", tVal, true},
+	{"if emptyslice", "{{if .SIEmpty}}NON-EMPTY{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"if slice", "{{if .SI}}NON-EMPTY{{else}}EMPTY{{end}}", "NON-EMPTY", tVal, true},
+	{"if emptymap", "{{if .MSIEmpty}}NON-EMPTY{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"if map", "{{if .MSI}}NON-EMPTY{{else}}EMPTY{{end}}", "NON-EMPTY", tVal, true},
+	// With.
+	{"with true", "{{with true}}{{.}}{{end}}", "true", tVal, true},
+	{"with false", "{{with false}}{{.}}{{else}}FALSE{{end}}", "FALSE", tVal, true},
+	{"with 1", "{{with 1}}{{.}}{{else}}ZERO{{end}}", "1", tVal, true},
+	{"with 0", "{{with 0}}{{.}}{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"with 1.5", "{{with 1.5}}{{.}}{{else}}ZERO{{end}}", "1.5", tVal, true},
+	{"with 0.0", "{{with .FloatZero}}{{.}}{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"with 1.5i", "{{with 1.5i}}{{.}}{{else}}ZERO{{end}}", "(0+1.5i)", tVal, true},
+	{"with 0.0i", "{{with .ComplexZero}}{{.}}{{else}}ZERO{{end}}", "ZERO", tVal, true},
+	{"with emptystring", "{{with ``}}{{.}}{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"with string", "{{with `notempty`}}{{.}}{{else}}EMPTY{{end}}", "notempty", tVal, true},
+	{"with emptyslice", "{{with .SIEmpty}}{{.}}{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"with slice", "{{with .SI}}{{.}}{{else}}EMPTY{{end}}", "[3 4 5]", tVal, true},
+	{"with emptymap", "{{with .MSIEmpty}}{{.}}{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"with map", "{{with .MSIone}}{{.}}{{else}}EMPTY{{end}}", "map[one:1]", tVal, true},
+	// Range.
 	{"range []int", "{{range .SI}}-{{.}}-{{end}}", "-3--4--5-", tVal, true},
-	{"range empty no else", "{{range .SEmpty}}-{{.}}-{{end}}", "", tVal, true},
+	{"range empty no else", "{{range .SIEmpty}}-{{.}}-{{end}}", "", tVal, true},
 	{"range []int else", "{{range .SI}}-{{.}}-{{else}}EMPTY{{end}}", "-3--4--5-", tVal, true},
-	{"range empty else", "{{range .SEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	{"range empty else", "{{range .SIEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
 	{"range []bool", "{{range .SB}}-{{.}}-{{end}}", "-true--false-", tVal, true},
 	{"range []int method", "{{range .SI | .MAdd .I}}-{{.}}-{{end}}", "-20--21--22-", tVal, true},
 	{"range map", "{{range .MSI | .MSort}}-{{.}}-{{end}}", "-one--three--two-", tVal, true},
 	{"range empty map no else", "{{range .MSIEmpty}}-{{.}}-{{end}}", "", tVal, true},
 	{"range map else", "{{range .MSI | .MSort}}-{{.}}-{{else}}EMPTY{{end}}", "-one--three--two-", tVal, true},
 	{"range empty map else", "{{range .MSIEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+	// Error handling.
 	{"error method, error", "{{.EPERM true}}", "", tVal, false},
 	{"error method, no error", "{{.EPERM false}}", "false", tVal, true},
 }
 
-func TestExecute(t *testing.T) {
+func testExecute(execTests []execTest, set *Set, t *testing.T) {
 	b := new(bytes.Buffer)
 	for _, test := range execTests {
 		tmpl := New(test.name)
@@ -128,7 +181,7 @@ func TestExecute(t *testing.T) {
 			continue
 		}
 		b.Reset()
-		err = tmpl.Execute(b, test.data)
+		err = tmpl.ExecuteInSet(b, test.data, set)
 		switch {
 		case !test.ok && err == nil:
 			t.Errorf("%s: expected error; got none", test.name)
@@ -146,6 +199,10 @@ func TestExecute(t *testing.T) {
 	}
 }
 
+func TestExecute(t *testing.T) {
+	testExecute(execTests, nil, t)
+}
+
 // Check that an error from a method flows back to the top.
 func TestExecuteError(t *testing.T) {
 	b := new(bytes.Buffer)
diff --git a/src/pkg/exp/template/parse.go b/src/pkg/exp/template/parse.go
index f1695557f4..74b5f2c0ae 100644
--- a/src/pkg/exp/template/parse.go
+++ b/src/pkg/exp/template/parse.go
@@ -11,6 +11,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"unicode"
 )
 
 // Template is the representation of a parsed template.
@@ -19,7 +20,7 @@ type Template struct {
 	root *listNode
 	// Parsing.
 	lex      *lexer
-	tokens   chan item
+	tokens   <-chan item
 	token    item // token lookahead for parser
 	havePeek bool
 }
@@ -70,10 +71,13 @@ const (
 	nodeEnd
 	nodeField
 	nodeIdentifier
+	nodeIf
 	nodeList
 	nodeNumber
 	nodeRange
 	nodeString
+	nodeTemplate
+	nodeWith
 )
 
 // Nodes.
@@ -215,31 +219,40 @@ func (b *boolNode) String() string {
 	return fmt.Sprintf("B=false")
 }
 
-// numberNode holds a number, signed or unsigned, integer, floating, or imaginary.
+// numberNode holds a number, signed or unsigned integer, floating, or complex.
 // The value is parsed and stored under all the types that can represent the value.
 // This simulates in a small amount of code the behavior of Go's ideal constants.
-// TODO: booleans, complex numbers.
 type numberNode struct {
 	nodeType
-	isInt     bool // number has an integral value
-	isUint    bool // number has an unsigned integral value
-	isFloat   bool // number has a floating-point value
-	imaginary bool // number is imaginary
-	int64          // the signed integer value
-	uint64         // the unsigned integer value
-	float64        // the positive floating-point value
-	text      string
-}
-
-func newNumber(text string) (*numberNode, os.Error) {
+	isInt      bool // number has an integral value
+	isUint     bool // number has an unsigned integral value
+	isFloat    bool // number has a floating-point value
+	isComplex  bool // number is complex
+	int64           // the signed integer value
+	uint64          // the unsigned integer value
+	float64         // the floating-point value
+	complex128      // the complex value
+	text       string
+}
+
+func newNumber(text string, isComplex bool) (*numberNode, os.Error) {
 	n := &numberNode{nodeType: nodeNumber, text: text}
-	// Imaginary constants can only be floating-point.
+	if isComplex {
+		// fmt.Sscan can parse the pair, so let it do the work.
+		if _, err := fmt.Sscan(text, &n.complex128); err != nil {
+			return nil, err
+		}
+		n.isComplex = true
+		n.simplifyComplex()
+		return n, nil
+	}
+	// Imaginary constants can only be complex unless they are zero.
 	if len(text) > 0 && text[len(text)-1] == 'i' {
 		f, err := strconv.Atof64(text[:len(text)-1])
 		if err == nil {
-			n.imaginary = true
-			n.isFloat = true
-			n.float64 = f
+			n.isComplex = true
+			n.complex128 = complex(0, f)
+			n.simplifyComplex()
 			return n, nil
 		}
 	}
@@ -287,6 +300,23 @@ func newNumber(text string) (*numberNode, os.Error) {
 	return n, nil
 }
 
+// simplifyComplex pulls out any other types that are represented by the complex number.
+// These all require that the imaginary part be zero.
+func (n *numberNode) simplifyComplex() {
+	n.isFloat = imag(n.complex128) == 0
+	if n.isFloat {
+		n.float64 = real(n.complex128)
+		n.isInt = float64(int64(n.float64)) == n.float64
+		if n.isInt {
+			n.int64 = int64(n.float64)
+		}
+		n.isUint = float64(uint64(n.float64)) == n.float64
+		if n.isUint {
+			n.uint64 = uint64(n.float64)
+		}
+	}
+}
+
 func (n *numberNode) String() string {
 	return fmt.Sprintf("N=%s", n.text)
 }
@@ -337,6 +367,26 @@ func (e *elseNode) typ() nodeType {
 func (e *elseNode) String() string {
 	return "{{else}}"
 }
+// ifNode represents an {{if}} action and its commands.
+// TODO: what should evaluation look like? is a pipeline enough?
+type ifNode struct {
+	nodeType
+	line     int
+	pipeline []*commandNode
+	list     *listNode
+	elseList *listNode
+}
+
+func newIf(line int, pipeline []*commandNode, list, elseList *listNode) *ifNode {
+	return &ifNode{nodeType: nodeIf, line: line, pipeline: pipeline, list: list, elseList: elseList}
+}
+
+func (i *ifNode) String() string {
+	if i.elseList != nil {
+		return fmt.Sprintf("({{if %s}} %s {{else}} %s)", i.pipeline, i.list, i.elseList)
+	}
+	return fmt.Sprintf("({{if %s}} %s)", i.pipeline, i.list)
+}
 
 // rangeNode represents a {{range}} action and its commands.
 type rangeNode struct {
@@ -347,8 +397,8 @@ type rangeNode struct {
 	elseList *listNode
 }
 
-func newRange(line int, pipeline []*commandNode, list *listNode) *rangeNode {
-	return &rangeNode{nodeType: nodeRange, line: line, pipeline: pipeline, list: list}
+func newRange(line int, pipeline []*commandNode, list, elseList *listNode) *rangeNode {
+	return &rangeNode{nodeType: nodeRange, line: line, pipeline: pipeline, list: list, elseList: elseList}
 }
 
 func (r *rangeNode) String() string {
@@ -358,6 +408,43 @@ func (r *rangeNode) String() string {
 	return fmt.Sprintf("({{range %s}} %s)", r.pipeline, r.list)
 }
 
+// templateNode represents a {{template}} action.
+type templateNode struct {
+	nodeType
+	line     int
+	name     node
+	pipeline []*commandNode
+}
+
+func newTemplate(line int, name node, pipeline []*commandNode) *templateNode {
+	return &templateNode{nodeType: nodeTemplate, line: line, name: name, pipeline: pipeline}
+}
+
+func (t *templateNode) String() string {
+	return fmt.Sprintf("{{template %s %s}}", t.name, t.pipeline)
+}
+
+// withNode represents a {{with}} action and its commands.
+type withNode struct {
+	nodeType
+	line     int
+	pipeline []*commandNode
+	list     *listNode
+	elseList *listNode
+}
+
+func newWith(line int, pipeline []*commandNode, list, elseList *listNode) *withNode {
+	return &withNode{nodeType: nodeWith, line: line, pipeline: pipeline, list: list, elseList: elseList}
+}
+
+func (w *withNode) String() string {
+	if w.elseList != nil {
+		return fmt.Sprintf("({{with %s}} %s {{else}} %s)", w.pipeline, w.list, w.elseList)
+	}
+	return fmt.Sprintf("({{with %s}} %s)", w.pipeline, w.list)
+}
+
+
 // Parsing.
 
 // New allocates a new template with the given name.
@@ -400,24 +487,62 @@ func (t *Template) recover(errp *os.Error) {
 		if _, ok := e.(runtime.Error); ok {
 			panic(e)
 		}
-		t.root, t.lex, t.tokens = nil, nil, nil
+		t.stopParse()
+		t.root = nil
 		*errp = e.(os.Error)
 	}
 	return
 }
 
+// startParse starts the template parsing from the lexer.
+func (t *Template) startParse(lex *lexer, tokens <-chan item) {
+	t.root = nil
+	t.lex, t.tokens = lex, tokens
+}
+
+// stopParse terminates parsing.
+func (t *Template) stopParse() {
+	t.lex, t.tokens = nil, nil
+}
+
+// atEOF returns true if, possibly after spaces, we're at EOF.
+func (t *Template) atEOF() bool {
+	for {
+		token := t.peek()
+		switch token.typ {
+		case itemEOF:
+			return true
+		case itemText:
+			for _, r := range token.val {
+				if !unicode.IsSpace(r) {
+					return false
+				}
+			}
+			t.next() // skip spaces.
+			continue
+		}
+		break
+	}
+	return false
+}
+
 // Parse parses the template definition string to construct an internal representation
 // of the template for execution.
 func (t *Template) Parse(s string) (err os.Error) {
-	t.lex, t.tokens = lex(t.name, s)
+	t.startParse(lex(t.name, s))
 	defer t.recover(&err)
-	var next node
+	t.parse(true)
+	t.stopParse()
+	return
+}
+
+// parse is the helper for Parse. It triggers an error if we expect EOF but don't reach it.
+func (t *Template) parse(toEOF bool) (next node) {
 	t.root, next = t.itemList(true)
-	if next != nil {
+	if toEOF && next != nil {
 		t.errorf("unexpected %s", next)
 	}
-	t.lex, t.tokens = nil, nil
-	return nil
+	return next
 }
 
 // itemList:
@@ -461,12 +586,18 @@ func (t *Template) textOrAction() node {
 // First word could be a keyword such as range.
 func (t *Template) action() (n node) {
 	switch token := t.next(); token.typ {
-	case itemRange:
-		return t.rangeControl()
 	case itemElse:
 		return t.elseControl()
 	case itemEnd:
 		return t.endControl()
+	case itemIf:
+		return t.ifControl()
+	case itemRange:
+		return t.rangeControl()
+	case itemTemplate:
+		return t.templateControl()
+	case itemWith:
+		return t.withControl()
 	}
 	t.backup()
 	return newAction(t.lex.lineNumber(), t.pipeline("command"))
@@ -479,14 +610,13 @@ func (t *Template) pipeline(context string) (pipe []*commandNode) {
 	for {
 		switch token := t.next(); token.typ {
 		case itemRightMeta:
+			if len(pipe) == 0 {
+				t.errorf("missing value for %s", context)
+			}
 			return
-		case itemIdentifier, itemField, itemDot:
+		case itemBool, itemComplex, itemDot, itemField, itemIdentifier, itemNumber, itemRawString, itemString:
 			t.backup()
-			cmd, err := t.command()
-			if err != nil {
-				t.error(err)
-			}
-			pipe = append(pipe, cmd)
+			pipe = append(pipe, t.command())
 		default:
 			t.unexpected(token, context)
 		}
@@ -494,26 +624,47 @@ func (t *Template) pipeline(context string) (pipe []*commandNode) {
 	return
 }
 
-// Range:
-//	{{range field}} itemList {{end}}
-//	{{range field}} itemList {{else}} itemList {{end}}
-// Range keyword is past.
-func (t *Template) rangeControl() node {
-	pipeline := t.pipeline("range")
-	list, next := t.itemList(false)
-	r := newRange(t.lex.lineNumber(), pipeline, list)
+func (t *Template) parseControl(context string) (lineNum int, pipe []*commandNode, list, elseList *listNode) {
+	pipe = t.pipeline(context)
+	var next node
+	list, next = t.itemList(false)
 	switch next.typ() {
 	case nodeEnd: //done
 	case nodeElse:
-		elseList, next := t.itemList(false)
+		elseList, next = t.itemList(false)
 		if next.typ() != nodeEnd {
 			t.errorf("expected end; found %s", next)
 		}
-		r.elseList = elseList
+		elseList = elseList
 	}
-	return r
+	return lineNum, pipe, list, elseList
+}
+
+// If:
+//	{{if pipeline}} itemList {{end}}
+//	{{if pipeline}} itemList {{else}} itemList {{end}}
+// If keyword is past.
+func (t *Template) ifControl() node {
+	return newIf(t.parseControl("if"))
 }
 
+// Range:
+//	{{range pipeline}} itemList {{end}}
+//	{{range pipeline}} itemList {{else}} itemList {{end}}
+// Range keyword is past.
+func (t *Template) rangeControl() node {
+	return newRange(t.parseControl("range"))
+}
+
+// With:
+//	{{with pipeline}} itemList {{end}}
+//	{{with pipeline}} itemList {{else}} itemList {{end}}
+// If keyword is past.
+func (t *Template) withControl() node {
+	return newWith(t.parseControl("with"))
+}
+
+
 // End:
 //	{{end}}
 // End keyword is past.
@@ -530,10 +681,36 @@ func (t *Template) elseControl() node {
 	return newElse(t.lex.lineNumber())
 }
 
+// Template:
+//	{{template stringValue pipeline}}
+// Template keyword is past.  The name must be something that can evaluate
+// to a string.
+func (t *Template) templateControl() node {
+	var name node
+	switch token := t.next(); token.typ {
+	case itemIdentifier:
+		name = newIdentifier(token.val)
+	case itemDot:
+		name = newDot()
+	case itemField:
+		name = newField(token.val)
+	case itemString, itemRawString:
+		s, err := strconv.Unquote(token.val)
+		if err != nil {
+			t.error(err)
+		}
+		name = newString(s)
+	default:
+		t.unexpected(token, "template invocation")
+	}
+	pipeline := t.pipeline("template")
+	return newTemplate(t.lex.lineNumber(), name, pipeline)
+}
+
 // command:
 // space-separated arguments up to a pipeline character or right metacharacter.
 // we consume the pipe character but leave the right meta to terminate the action.
-func (t *Template) command() (*commandNode, os.Error) {
+func (t *Template) command() *commandNode {
 	cmd := newCommand()
 Loop:
 	for {
@@ -544,7 +721,7 @@ Loop:
 		case itemPipe:
 			break Loop
 		case itemError:
-			return nil, os.NewError(token.val)
+			t.errorf("%s", token.val)
 		case itemIdentifier:
 			cmd.append(newIdentifier(token.val))
 		case itemDot:
@@ -553,22 +730,16 @@ Loop:
 			cmd.append(newField(token.val))
 		case itemBool:
 			cmd.append(newBool(token.val == "true"))
-		case itemNumber:
-			if len(cmd.args) == 0 {
-				t.errorf("command cannot be %q", token.val)
-			}
-			number, err := newNumber(token.val)
+		case itemComplex, itemNumber:
+			number, err := newNumber(token.val, token.typ == itemComplex)
 			if err != nil {
 				t.error(err)
 			}
 			cmd.append(number)
 		case itemString, itemRawString:
-			if len(cmd.args) == 0 {
-				t.errorf("command cannot be %q", token.val)
-			}
 			s, err := strconv.Unquote(token.val)
 			if err != nil {
-				return nil, err
+				t.error(err)
 			}
 			cmd.append(newString(s))
 		default:
@@ -578,5 +749,5 @@ Loop:
 	if len(cmd.args) == 0 {
 		t.errorf("empty command")
 	}
-	return cmd, nil
+	return cmd
 }
diff --git a/src/pkg/exp/template/parse_test.go b/src/pkg/exp/template/parse_test.go
index b1da989cf2..5c780cd292 100644
--- a/src/pkg/exp/template/parse_test.go
+++ b/src/pkg/exp/template/parse_test.go
@@ -16,41 +16,53 @@ type numberTest struct {
 	isInt     bool
 	isUint    bool
 	isFloat   bool
-	imaginary bool
+	isComplex bool
 	int64
 	uint64
 	float64
+	complex128
 }
 
 var numberTests = []numberTest{
 	// basics
-	{"0", true, true, true, false, 0, 0, 0},
-	{"-0", true, true, true, false, 0, 0, 0}, // check that -0 is a uint.
-	{"73", true, true, true, false, 73, 73, 73},
-	{"-73", true, false, true, false, -73, 0, -73},
-	{"+73", true, false, true, false, 73, 0, 73},
-	{"100", true, true, true, false, 100, 100, 100},
-	{"1e9", true, true, true, false, 1e9, 1e9, 1e9},
-	{"-1e9", true, false, true, false, -1e9, 0, -1e9},
-	{"-1.2", false, false, true, false, 0, 0, -1.2},
-	{"1e19", false, true, true, false, 0, 1e19, 1e19},
-	{"-1e19", false, false, true, false, 0, 0, -1e19},
-	{"4i", false, false, true, true, 0, 0, 4},
+	{"0", true, true, true, false, 0, 0, 0, 0},
+	{"-0", true, true, true, false, 0, 0, 0, 0}, // check that -0 is a uint.
+	{"73", true, true, true, false, 73, 73, 73, 0},
+	{"-73", true, false, true, false, -73, 0, -73, 0},
+	{"+73", true, false, true, false, 73, 0, 73, 0},
+	{"100", true, true, true, false, 100, 100, 100, 0},
+	{"1e9", true, true, true, false, 1e9, 1e9, 1e9, 0},
+	{"-1e9", true, false, true, false, -1e9, 0, -1e9, 0},
+	{"-1.2", false, false, true, false, 0, 0, -1.2, 0},
+	{"1e19", false, true, true, false, 0, 1e19, 1e19, 0},
+	{"-1e19", false, false, true, false, 0, 0, -1e19, 0},
+	{"4i", false, false, false, true, 0, 0, 0, 4i},
+	{"-1.2+4.2i", false, false, false, true, 0, 0, 0, -1.2 + 4.2i},
+	// complex with 0 imaginary are float (and maybe integer)
+	{"0i", true, true, true, true, 0, 0, 0, 0},
+	{"-1.2+0i", false, false, true, true, 0, 0, -1.2, -1.2},
+	{"-12+0i", true, false, true, true, -12, 0, -12, -12},
+	{"13+0i", true, true, true, true, 13, 13, 13, 13},
 	// funny bases
-	{"0123", true, true, true, false, 0123, 0123, 0123},
-	{"-0x0", true, true, true, false, 0, 0, 0},
-	{"0xdeadbeef", true, true, true, false, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef},
+	{"0123", true, true, true, false, 0123, 0123, 0123, 0},
+	{"-0x0", true, true, true, false, 0, 0, 0, 0},
+	{"0xdeadbeef", true, true, true, false, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0},
 	// some broken syntax
 	{text: "+-2"},
 	{text: "0x123."},
 	{text: "1e."},
 	{text: "0xi."},
+	{text: "1+2."},
 }
 
 func TestNumberParse(t *testing.T) {
 	for _, test := range numberTests {
-		n, err := newNumber(test.text)
-		ok := test.isInt || test.isUint || test.isFloat
+		// If fmt.Sscan thinks it's complex, it's complex.  We can't trust the output
+		// because imaginary comes out as a number.
+		var c complex128
+		_, err := fmt.Sscan(test.text, &c)
+		n, err := newNumber(test.text, err == nil)
+		ok := test.isInt || test.isUint || test.isFloat || test.isComplex
 		if ok && err != nil {
 			t.Errorf("unexpected error for %q", test.text)
 			continue
@@ -62,8 +74,8 @@ func TestNumberParse(t *testing.T) {
 		if !ok {
 			continue
 		}
-		if n.imaginary != test.imaginary {
-			t.Errorf("imaginary incorrect for %q; should be %t", test.text, test.imaginary)
+		if n.isComplex != test.isComplex {
+			t.Errorf("complex incorrect for %q; should be %t", test.text, test.isComplex)
 		}
 		if test.isInt {
 			if !n.isInt {
@@ -95,17 +107,19 @@ func TestNumberParse(t *testing.T) {
 		} else if n.isFloat {
 			t.Errorf("did not expect float for %q", test.text)
 		}
+		if test.isComplex {
+			if !n.isComplex {
+				t.Errorf("expected complex for %q", test.text)
+			}
+			if n.complex128 != test.complex128 {
+				t.Errorf("complex128 for %q should be %g is %g", test.text, test.complex128, n.complex128)
+			}
+		} else if n.isComplex {
+			t.Errorf("did not expect complex for %q", test.text)
+		}
 	}
 }
 
-func num(s string) *numberNode {
-	n, err := newNumber(s)
-	if err != nil {
-		panic(err)
-	}
-	return n
-}
-
 type parseTest struct {
 	name   string
 	input  string
@@ -125,7 +139,7 @@ var parseTests = []parseTest{
 		`[(text: " \t\n")]`},
 	{"text", "some text", noError,
 		`[(text: "some text")]`},
-	{"emptyMeta", "{{}}", noError,
+	{"emptyMeta", "{{}}", hasError,
 		`[(action: [])]`},
 	{"field", "{{.X}}", noError,
 		`[(action: [(command: [F=[X]])])]`},
@@ -139,6 +153,10 @@ var parseTests = []parseTest{
 		"[(action: [(command: [I=hello S=`quoted text`])])]"},
 	{"pipeline", "{{hello|world}}", noError,
 		`[(action: [(command: [I=hello]) (command: [I=world])])]`},
+	{"simple if", "{{if .X}}hello{{end}}", noError,
+		`[({{if [(command: [F=[X]])]}} [(text: "hello")])]`},
+	{"if with else", "{{if .X}}true{{else}}false{{end}}", noError,
+		`[({{if [(command: [F=[X]])]}} [(text: "true")] {{else}} [(text: "false")])]`},
 	{"simple range", "{{range .X}}hello{{end}}", noError,
 		`[({{range [(command: [F=[X]])]}} [(text: "hello")])]`},
 	{"chained field range", "{{range .X.Y.Z}}hello{{end}}", noError,
@@ -153,6 +171,12 @@ var parseTests = []parseTest{
 		`[({{range [(command: [F=[SI]])]}} [(action: [(command: [{{<.>}}])])])]`},
 	{"constants", "{{range .SI 1 -3.2i true false }}{{end}}", noError,
 		`[({{range [(command: [F=[SI] N=1 N=-3.2i B=true B=false])]}} [])]`},
+	{"template", "{{template foo .X}}", noError,
+		"[{{template I=foo [(command: [F=[X]])]}}]"},
+	{"with", "{{with .X}}hello{{end}}", noError,
+		`[({{with [(command: [F=[X]])]}} [(text: "hello")])]`},
+	{"with with else", "{{with .X}}hello{{else}}goodbye{{end}}", noError,
+		`[({{with [(command: [F=[X]])]}} [(text: "hello")] {{else}} [(text: "goodbye")])]`},
 	// Errors.
 	{"unclosed action", "hello{{range", hasError, ""},
 	{"missing end", "hello{{range .x}}", hasError, ""},
diff --git a/src/pkg/exp/template/set.go b/src/pkg/exp/template/set.go
new file mode 100644
index 0000000000..13d93d03ca
--- /dev/null
+++ b/src/pkg/exp/template/set.go
@@ -0,0 +1,71 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"os"
+	"runtime"
+	"strconv"
+)
+
+// Set holds a set of related templates that can refer to one another by name.
+// A template may be a member of multiple sets.
+type Set struct {
+	tmpl map[string]*Template
+}
+
+// NewSet allocates a new, empty template set.
+func NewSet() *Set {
+	return &Set{
+		tmpl: make(map[string]*Template),
+	}
+}
+
+// recover is the handler that turns panics into returns from the top
+// level of Parse.
+func (s *Set) recover(errp *os.Error) {
+	e := recover()
+	if e != nil {
+		if _, ok := e.(runtime.Error); ok {
+			panic(e)
+		}
+		s.tmpl = nil
+		*errp = e.(os.Error)
+	}
+	return
+}
+
+// Parse parses the file into a set of named templates.
+func (s *Set) Parse(text string) (err os.Error) {
+	defer s.recover(&err)
+	lex, tokens := lex("set", text)
+	const context = "define clause"
+	for {
+		t := New("set") // name will be updated once we know it.
+		t.startParse(lex, tokens)
+		// Expect EOF or "{{ define name }}".
+		if t.atEOF() {
+			return
+		}
+		t.expect(itemLeftMeta, context)
+		t.expect(itemDefine, context)
+		name := t.expect(itemString, context)
+		t.name, err = strconv.Unquote(name.val)
+		if err != nil {
+			t.error(err)
+		}
+		t.expect(itemRightMeta, context)
+		end := t.parse(false)
+		if end == nil {
+			t.errorf("unexpected EOF in %s", context)
+		}
+		if end.typ() != nodeEnd {
+			t.errorf("unexpected %s in %s", end, context)
+		}
+		t.stopParse()
+		s.tmpl[t.name] = t
+	}
+	return nil
+}
diff --git a/src/pkg/exp/template/set_test.go b/src/pkg/exp/template/set_test.go
new file mode 100644
index 0000000000..873d261b3d
--- /dev/null
+++ b/src/pkg/exp/template/set_test.go
@@ -0,0 +1,101 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"fmt"
+	"testing"
+)
+
+type setParseTest struct {
+	name    string
+	input   string
+	ok      bool
+	names   []string
+	results []string
+}
+
+var setParseTests = []setParseTest{
+	{"empty", "", noError,
+		nil,
+		nil},
+	{"one", `{{define "foo"}} FOO {{end}}`, noError,
+		[]string{"foo"},
+		[]string{`[(text: " FOO ")]`}},
+	{"two", `{{define "foo"}} FOO {{end}}{{define "bar"}} BAR {{end}}`, noError,
+		[]string{"foo", "bar"},
+		[]string{`[(text: " FOO ")]`, `[(text: " BAR ")]`}},
+	// errors
+	{"missing end", `{{define "foo"}} FOO `, hasError,
+		nil,
+		nil},
+	{"malformed name", `{{define "foo}} FOO `, hasError,
+		nil,
+		nil},
+}
+
+func TestSetParse(t *testing.T) {
+	for _, test := range setParseTests {
+		set := NewSet()
+		err := set.Parse(test.input)
+		switch {
+		case err == nil && !test.ok:
+			t.Errorf("%q: expected error; got none", test.name)
+			continue
+		case err != nil && test.ok:
+			t.Errorf("%q: unexpected error: %v", test.name, err)
+			continue
+		case err != nil && !test.ok:
+			// expected error, got one
+			if dumpErrors {
+				fmt.Printf("%s: %s\n\t%s\n", test.name, test.input, err)
+			}
+			continue
+		}
+		if len(set.tmpl) != len(test.names) {
+			t.Errorf("%s: wrong number of templates; wanted %d got %d", test.name, len(test.names), len(set.tmpl))
+			continue
+		}
+		for i, name := range test.names {
+			tmpl, ok := set.tmpl[name]
+			if !ok {
+				t.Errorf("%s: can't find template %q", test.name, name)
+				continue
+			}
+			result := tmpl.root.String()
+			if result != test.results[i] {
+				t.Errorf("%s=(%q): got\n\t%v\nexpected\n\t%v", test.name, test.input, result, test.results[i])
+			}
+		}
+	}
+}
+
+
+var setExecTests = []execTest{
+	{"empty", "", "", nil, true},
+	{"text", "some text", "some text", nil, true},
+	{"invoke text", `{{template "text" .SI}}`, "TEXT", tVal, true},
+	{"invoke dot int", `{{template "dot" .I}}`, "17", tVal, true},
+	{"invoke dot []int", `{{template "dot" .SI}}`, "[3 4 5]", tVal, true},
+	{"invoke dotV", `{{template "dotV" .U}}`, "v", tVal, true},
+	{"invoke nested int", `{{template "nested" .I}}`, "17", tVal, true},
+}
+
+const setText = `
+	{{define "text"}}TEXT{{end}}
+	{{define "dotV"}}{{.V}}{{end}}
+	{{define "dot"}}{{.}}{{end}}
+	{{define "nested"}}{{template "dot" .}}{{end}}
+`
+
+func TestSetExecute(t *testing.T) {
+	// Declare a set with a couple of templates first.
+	set := NewSet()
+	err := set.Parse(setText)
+	if err != nil {
+		t.Fatalf("error parsing set: %s", err)
+	}
+	testExecute(setExecTests, set, t)
+}