Add Go frontend, libgo library, and Go testsuite.

[thirdparty/gcc.git] / libgo / go / template / template.go

// Copyright 2009 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.

/*
        Data-driven templates for generating textual output such as
        HTML.

        Templates are executed by applying them to a data structure.
        Annotations in the template refer to elements of the data
        structure (typically a field of a struct or a key in a map)
        to control execution and derive values to be displayed.
        The template walks the structure as it executes and the
        "cursor" @ represents the value at the current location
        in the structure.

        Data items may be values or pointers; the interface hides the
        indirection.

        In the following, 'field' is one of several things, according to the data.

                - The name of a field of a struct (result = data.field),
                - The value stored in a map under that key (result = data[field]), or
                - The result of invoking a niladic single-valued method with that name
                  (result = data.field())

        Major constructs ({} are metacharacters; [] marks optional elements):

                {# comment }

        A one-line comment.

                {.section field} XXX [ {.or} YYY ] {.end}

        Set @ to the value of the field.  It may be an explicit @
        to stay at the same point in the data. If the field is nil
        or empty, execute YYY; otherwise execute XXX.

                {.repeated section field} XXX [ {.alternates with} ZZZ ] [ {.or} YYY ] {.end}

        Like .section, but field must be an array or slice.  XXX
        is executed for each element.  If the array is nil or empty,
        YYY is executed instead.  If the {.alternates with} marker
        is present, ZZZ is executed between iterations of XXX.

                {field}
                {field|formatter}

        Insert the value of the field into the output. Field is
        first looked for in the cursor, as in .section and .repeated.
        If it is not found, the search continues in outer sections
        until the top level is reached.

        If a formatter is specified, it must be named in the formatter
        map passed to the template set up routines or in the default
        set ("html","str","") and is used to process the data for
        output.  The formatter function has signature
                func(wr io.Writer, data interface{}, formatter string)
        where wr is the destination for output, data is the field
        value, and formatter is its name at the invocation site.
*/
package template

import (
        "container/vector"
        "fmt"
        "io"
        "io/ioutil"
        "os"
        "reflect"
        "strings"
)

// Errors returned during parsing and execution.  Users may extract the information and reformat
// if they desire.
type Error struct {
        Line int
        Msg  string
}

func (e *Error) String() string { return fmt.Sprintf("line %d: %s", e.Line, e.Msg) }

// Most of the literals are aces.
var lbrace = []byte{'{'}
var rbrace = []byte{'}'}
var space = []byte{' '}
var tab = []byte{'\t'}

// The various types of "tokens", which are plain text or (usually) brace-delimited descriptors
const (
        tokAlternates = iota
        tokComment
        tokEnd
        tokLiteral
        tokOr
        tokRepeated
        tokSection
        tokText
        tokVariable
)

// FormatterMap is the type describing the mapping from formatter
// names to the functions that implement them.
type FormatterMap map[string]func(io.Writer, interface{}, string)

// Built-in formatters.
var builtins = FormatterMap{
        "html": HTMLFormatter,
        "str":  StringFormatter,
        "":     StringFormatter,
}

// The parsed state of a template is a vector of xxxElement structs.
// Sections have line numbers so errors can be reported better during execution.

// Plain text.
type textElement struct {
        text []byte
}

// A literal such as .meta-left or .meta-right
type literalElement struct {
        text []byte
}

// A variable to be evaluated
type variableElement struct {
        linenum   int
        name      string
        formatter string // TODO(r): implement pipelines
}

// A .section block, possibly with a .or
type sectionElement struct {
        linenum int    // of .section itself
        field   string // cursor field for this block
        start   int    // first element
        or      int    // first element of .or block
        end     int    // one beyond last element
}

// A .repeated block, possibly with a .or and a .alternates
type repeatedElement struct {
        sectionElement     // It has the same structure...
        altstart       int // ... except for alternates
        altend         int
}

// Template is the type that represents a template definition.
// It is unchanged after parsing.
type Template struct {
        fmap FormatterMap // formatters for variables
        // Used during parsing:
        ldelim, rdelim []byte // delimiters; default {}
        buf            []byte // input text to process
        p              int    // position in buf
        linenum        int    // position in input
        // Parsed results:
        elems *vector.Vector
}

// Internal state for executing a Template.  As we evaluate the struct,
// the data item descends into the fields associated with sections, etc.
// Parent is used to walk upwards to find variables higher in the tree.
type state struct {
        parent *state        // parent in hierarchy
        data   reflect.Value // the driver data for this section etc.
        wr     io.Writer     // where to send output
}

func (parent *state) clone(data reflect.Value) *state {
        return &state{parent, data, parent.wr}
}

// New creates a new template with the specified formatter map (which
// may be nil) to define auxiliary functions for formatting variables.
func New(fmap FormatterMap) *Template {
        t := new(Template)
        t.fmap = fmap
        t.ldelim = lbrace
        t.rdelim = rbrace
        t.elems = new(vector.Vector)
        return t
}

// Report error and stop executing.  The line number must be provided explicitly.
func (t *Template) execError(st *state, line int, err string, args ...interface{}) {
        panic(&Error{line, fmt.Sprintf(err, args...)})
}

// Report error, panic to terminate parsing.
// The line number comes from the template state.
func (t *Template) parseError(err string, args ...interface{}) {
        panic(&Error{t.linenum, fmt.Sprintf(err, args...)})
}

// -- Lexical analysis

// Is c a white space character?
func white(c uint8) bool { return c == ' ' || c == '\t' || c == '\r' || c == '\n' }

// Safely, does s[n:n+len(t)] == t?
func equal(s []byte, n int, t []byte) bool {
        b := s[n:]
        if len(t) > len(b) { // not enough space left for a match.
                return false
        }
        for i, c := range t {
                if c != b[i] {
                        return false
                }
        }
        return true
}

// nextItem returns the next item from the input buffer.  If the returned
// item is empty, we are at EOF.  The item will be either a
// delimited string or a non-empty string between delimited
// strings. Tokens stop at (but include, if plain text) a newline.
// Action tokens on a line by themselves drop any space on
// either side, up to and including the newline.
func (t *Template) nextItem() []byte {
        startOfLine := t.p == 0 || t.buf[t.p-1] == '\n'
        start := t.p
        var i int
        newline := func() {
                t.linenum++
                i++
        }
        // Leading white space up to but not including newline
        for i = start; i < len(t.buf); i++ {
                if t.buf[i] == '\n' || !white(t.buf[i]) {
                        break
                }
        }
        leadingSpace := i > start
        // What's left is nothing, newline, delimited string, or plain text
Switch:
        switch {
        case i == len(t.buf):
                // EOF; nothing to do
        case t.buf[i] == '\n':
                newline()
        case equal(t.buf, i, t.ldelim):
                left := i         // Start of left delimiter.
                right := -1       // Will be (immediately after) right delimiter.
                haveText := false // Delimiters contain text.
                i += len(t.ldelim)
                // Find the end of the action.
                for ; i < len(t.buf); i++ {
                        if t.buf[i] == '\n' {
                                break
                        }
                        if equal(t.buf, i, t.rdelim) {
                                i += len(t.rdelim)
                                right = i
                                break
                        }
                        haveText = true
                }
                if right < 0 {
                        t.parseError("unmatched opening delimiter")
                        return nil
                }
                // Is this a special action (starts with '.' or '#') and the only thing on the line?
                if startOfLine && haveText {
                        firstChar := t.buf[left+len(t.ldelim)]
                        if firstChar == '.' || firstChar == '#' {
                                // It's special and the first thing on the line. Is it the last?
                                for j := right; j < len(t.buf) && white(t.buf[j]); j++ {
                                        if t.buf[j] == '\n' {
                                                // Yes it is. Drop the surrounding space and return the {.foo}
                                                t.linenum++
                                                t.p = j + 1
                                                return t.buf[left:right]
                                        }
                                }
                        }
                }
                // No it's not. If there's leading space, return that.
                if leadingSpace {
                        // not trimming space: return leading white space if there is some.
                        t.p = left
                        return t.buf[start:left]
                }
                // Return the word, leave the trailing space.
                start = left
                break
        default:
                for ; i < len(t.buf); i++ {
                        if t.buf[i] == '\n' {
                                newline()
                                break
                        }
                        if equal(t.buf, i, t.ldelim) {
                                break
                        }
                }
        }
        item := t.buf[start:i]
        t.p = i
        return item
}

// Turn a byte array into a white-space-split array of strings.
func words(buf []byte) []string {
        s := make([]string, 0, 5)
        p := 0 // position in buf
        // one word per loop
        for i := 0; ; i++ {
                // skip white space
                for ; p < len(buf) && white(buf[p]); p++ {
                }
                // grab word
                start := p
                for ; p < len(buf) && !white(buf[p]); p++ {
                }
                if start == p { // no text left
                        break
                }
                s = append(s, string(buf[start:p]))
        }
        return s
}

// Analyze an item and return its token type and, if it's an action item, an array of
// its constituent words.
func (t *Template) analyze(item []byte) (tok int, w []string) {
        // item is known to be non-empty
        if !equal(item, 0, t.ldelim) { // doesn't start with left delimiter
                tok = tokText
                return
        }
        if !equal(item, len(item)-len(t.rdelim), t.rdelim) { // doesn't end with right delimiter
                t.parseError("internal error: unmatched opening delimiter") // lexing should prevent this
                return
        }
        if len(item) <= len(t.ldelim)+len(t.rdelim) { // no contents
                t.parseError("empty directive")
                return
        }
        // Comment
        if item[len(t.ldelim)] == '#' {
                tok = tokComment
                return
        }
        // Split into words
        w = words(item[len(t.ldelim) : len(item)-len(t.rdelim)]) // drop final delimiter
        if len(w) == 0 {
                t.parseError("empty directive")
                return
        }
        if len(w) == 1 && w[0][0] != '.' {
                tok = tokVariable
                return
        }
        switch w[0] {
        case ".meta-left", ".meta-right", ".space", ".tab":
                tok = tokLiteral
                return
        case ".or":
                tok = tokOr
                return
        case ".end":
                tok = tokEnd
                return
        case ".section":
                if len(w) != 2 {
                        t.parseError("incorrect fields for .section: %s", item)
                        return
                }
                tok = tokSection
                return
        case ".repeated":
                if len(w) != 3 || w[1] != "section" {
                        t.parseError("incorrect fields for .repeated: %s", item)
                        return
                }
                tok = tokRepeated
                return
        case ".alternates":
                if len(w) != 2 || w[1] != "with" {
                        t.parseError("incorrect fields for .alternates: %s", item)
                        return
                }
                tok = tokAlternates
                return
        }
        t.parseError("bad directive: %s", item)
        return
}

// -- Parsing

// Allocate a new variable-evaluation element.
func (t *Template) newVariable(name_formatter string) (v *variableElement) {
        name := name_formatter
        formatter := ""
        bar := strings.Index(name_formatter, "|")
        if bar >= 0 {
                name = name_formatter[0:bar]
                formatter = name_formatter[bar+1:]
        }
        // Probably ok, so let's build it.
        v = &variableElement{t.linenum, name, formatter}

        // We could remember the function address here and avoid the lookup later,
        // but it's more dynamic to let the user change the map contents underfoot.
        // We do require the name to be present, though.

        // Is it in user-supplied map?
        if t.fmap != nil {
                if _, ok := t.fmap[formatter]; ok {
                        return
                }
        }
        // Is it in builtin map?
        if _, ok := builtins[formatter]; ok {
                return
        }
        t.parseError("unknown formatter: %s", formatter)
        return
}

// Grab the next item.  If it's simple, just append it to the template.
// Otherwise return its details.
func (t *Template) parseSimple(item []byte) (done bool, tok int, w []string) {
        tok, w = t.analyze(item)
        done = true // assume for simplicity
        switch tok {
        case tokComment:
                return
        case tokText:
                t.elems.Push(&textElement{item})
                return
        case tokLiteral:
                switch w[0] {
                case ".meta-left":
                        t.elems.Push(&literalElement{t.ldelim})
                case ".meta-right":
                        t.elems.Push(&literalElement{t.rdelim})
                case ".space":
                        t.elems.Push(&literalElement{space})
                case ".tab":
                        t.elems.Push(&literalElement{tab})
                default:
                        t.parseError("internal error: unknown literal: %s", w[0])
                }
                return
        case tokVariable:
                t.elems.Push(t.newVariable(w[0]))
                return
        }
        return false, tok, w
}

// parseRepeated and parseSection are mutually recursive

func (t *Template) parseRepeated(words []string) *repeatedElement {
        r := new(repeatedElement)
        t.elems.Push(r)
        r.linenum = t.linenum
        r.field = words[2]
        // Scan section, collecting true and false (.or) blocks.
        r.start = t.elems.Len()
        r.or = -1
        r.altstart = -1
        r.altend = -1
Loop:
        for {
                item := t.nextItem()
                if len(item) == 0 {
                        t.parseError("missing .end for .repeated section")
                        break
                }
                done, tok, w := t.parseSimple(item)
                if done {
                        continue
                }
                switch tok {
                case tokEnd:
                        break Loop
                case tokOr:
                        if r.or >= 0 {
                                t.parseError("extra .or in .repeated section")
                                break Loop
                        }
                        r.altend = t.elems.Len()
                        r.or = t.elems.Len()
                case tokSection:
                        t.parseSection(w)
                case tokRepeated:
                        t.parseRepeated(w)
                case tokAlternates:
                        if r.altstart >= 0 {
                                t.parseError("extra .alternates in .repeated section")
                                break Loop
                        }
                        if r.or >= 0 {
                                t.parseError(".alternates inside .or block in .repeated section")
                                break Loop
                        }
                        r.altstart = t.elems.Len()
                default:
                        t.parseError("internal error: unknown repeated section item: %s", item)
                        break Loop
                }
        }
        if r.altend < 0 {
                r.altend = t.elems.Len()
        }
        r.end = t.elems.Len()
        return r
}

func (t *Template) parseSection(words []string) *sectionElement {
        s := new(sectionElement)
        t.elems.Push(s)
        s.linenum = t.linenum
        s.field = words[1]
        // Scan section, collecting true and false (.or) blocks.
        s.start = t.elems.Len()
        s.or = -1
Loop:
        for {
                item := t.nextItem()
                if len(item) == 0 {
                        t.parseError("missing .end for .section")
                        break
                }
                done, tok, w := t.parseSimple(item)
                if done {
                        continue
                }
                switch tok {
                case tokEnd:
                        break Loop
                case tokOr:
                        if s.or >= 0 {
                                t.parseError("extra .or in .section")
                                break Loop
                        }
                        s.or = t.elems.Len()
                case tokSection:
                        t.parseSection(w)
                case tokRepeated:
                        t.parseRepeated(w)
                case tokAlternates:
                        t.parseError(".alternates not in .repeated")
                default:
                        t.parseError("internal error: unknown section item: %s", item)
                }
        }
        s.end = t.elems.Len()
        return s
}

func (t *Template) parse() {
        for {
                item := t.nextItem()
                if len(item) == 0 {
                        break
                }
                done, tok, w := t.parseSimple(item)
                if done {
                        continue
                }
                switch tok {
                case tokOr, tokEnd, tokAlternates:
                        t.parseError("unexpected %s", w[0])
                case tokSection:
                        t.parseSection(w)
                case tokRepeated:
                        t.parseRepeated(w)
                default:
                        t.parseError("internal error: bad directive in parse: %s", item)
                }
        }
}

// -- Execution

// Evaluate interfaces and pointers looking for a value that can look up the name, via a
// struct field, method, or map key, and return the result of the lookup.
func lookup(v reflect.Value, name string) reflect.Value {
        for v != nil {
                typ := v.Type()
                if n := v.Type().NumMethod(); n > 0 {
                        for i := 0; i < n; i++ {
                                m := typ.Method(i)
                                mtyp := m.Type
                                if m.Name == name && mtyp.NumIn() == 1 && mtyp.NumOut() == 1 {
                                        return v.Method(i).Call(nil)[0]
                                }
                        }
                }
                switch av := v.(type) {
                case *reflect.PtrValue:
                        v = av.Elem()
                case *reflect.InterfaceValue:
                        v = av.Elem()
                case *reflect.StructValue:
                        return av.FieldByName(name)
                case *reflect.MapValue:
                        return av.Elem(reflect.NewValue(name))
                default:
                        return nil
                }
        }
        return v
}

// Walk v through pointers and interfaces, extracting the elements within.
func indirect(v reflect.Value) reflect.Value {
loop:
        for v != nil {
                switch av := v.(type) {
                case *reflect.PtrValue:
                        v = av.Elem()
                case *reflect.InterfaceValue:
                        v = av.Elem()
                default:
                        break loop
                }
        }
        return v
}

// If the data for this template is a struct, find the named variable.
// Names of the form a.b.c are walked down the data tree.
// The special name "@" (the "cursor") denotes the current data.
// The value coming in (st.data) might need indirecting to reach
// a struct while the return value is not indirected - that is,
// it represents the actual named field.
func (st *state) findVar(s string) reflect.Value {
        if s == "@" {
                return st.data
        }
        data := st.data
        for _, elem := range strings.Split(s, ".", -1) {
                // Look up field; data must be a struct or map.
                data = lookup(data, elem)
                if data == nil {
                        return nil
                }
        }
        return data
}

// Is there no data to look at?
func empty(v reflect.Value) bool {
        v = indirect(v)
        if v == nil {
                return true
        }
        switch v := v.(type) {
        case *reflect.BoolValue:
                return v.Get() == false
        case *reflect.StringValue:
                return v.Get() == ""
        case *reflect.StructValue:
                return false
        case *reflect.MapValue:
                return false
        case *reflect.ArrayValue:
                return v.Len() == 0
        case *reflect.SliceValue:
                return v.Len() == 0
        }
        return true
}

// Look up a variable or method, up through the parent if necessary.
func (t *Template) varValue(name string, st *state) reflect.Value {
        field := st.findVar(name)
        if field == nil {
                if st.parent == nil {
                        t.execError(st, t.linenum, "name not found: %s in type %s", name, st.data.Type())
                }
                return t.varValue(name, st.parent)
        }
        return field
}

// Evaluate a variable, looking up through the parent if necessary.
// If it has a formatter attached ({var|formatter}) run that too.
func (t *Template) writeVariable(v *variableElement, st *state) {
        formatter := v.formatter
        val := t.varValue(v.name, st).Interface()
        // is it in user-supplied map?
        if t.fmap != nil {
                if fn, ok := t.fmap[formatter]; ok {
                        fn(st.wr, val, formatter)
                        return
                }
        }
        // is it in builtin map?
        if fn, ok := builtins[formatter]; ok {
                fn(st.wr, val, formatter)
                return
        }
        t.execError(st, v.linenum, "missing formatter %s for variable %s", formatter, v.name)
}

// Execute element i.  Return next index to execute.
func (t *Template) executeElement(i int, st *state) int {
        switch elem := t.elems.At(i).(type) {
        case *textElement:
                st.wr.Write(elem.text)
                return i + 1
        case *literalElement:
                st.wr.Write(elem.text)
                return i + 1
        case *variableElement:
                t.writeVariable(elem, st)
                return i + 1
        case *sectionElement:
                t.executeSection(elem, st)
                return elem.end
        case *repeatedElement:
                t.executeRepeated(elem, st)
                return elem.end
        }
        e := t.elems.At(i)
        t.execError(st, 0, "internal error: bad directive in execute: %v %T\n", reflect.NewValue(e).Interface(), e)
        return 0
}

// Execute the template.
func (t *Template) execute(start, end int, st *state) {
        for i := start; i < end; {
                i = t.executeElement(i, st)
        }
}

// Execute a .section
func (t *Template) executeSection(s *sectionElement, st *state) {
        // Find driver data for this section.  It must be in the current struct.
        field := t.varValue(s.field, st)
        if field == nil {
                t.execError(st, s.linenum, ".section: cannot find field %s in %s", s.field, st.data.Type())
        }
        st = st.clone(field)
        start, end := s.start, s.or
        if !empty(field) {
                // Execute the normal block.
                if end < 0 {
                        end = s.end
                }
        } else {
                // Execute the .or block.  If it's missing, do nothing.
                start, end = s.or, s.end
                if start < 0 {
                        return
                }
        }
        for i := start; i < end; {
                i = t.executeElement(i, st)
        }
}

// Return the result of calling the Iter method on v, or nil.
func iter(v reflect.Value) *reflect.ChanValue {
        for j := 0; j < v.Type().NumMethod(); j++ {
                mth := v.Type().Method(j)
                fv := v.Method(j)
                ft := fv.Type().(*reflect.FuncType)
                // TODO(rsc): NumIn() should return 0 here, because ft is from a curried FuncValue.
                if mth.Name != "Iter" || ft.NumIn() != 1 || ft.NumOut() != 1 {
                        continue
                }
                ct, ok := ft.Out(0).(*reflect.ChanType)
                if !ok || ct.Dir()&reflect.RecvDir == 0 {
                        continue
                }
                return fv.Call(nil)[0].(*reflect.ChanValue)
        }
        return nil
}

// Execute a .repeated section
func (t *Template) executeRepeated(r *repeatedElement, st *state) {
        // Find driver data for this section.  It must be in the current struct.
        field := t.varValue(r.field, st)
        if field == nil {
                t.execError(st, r.linenum, ".repeated: cannot find field %s in %s", r.field, st.data.Type())
        }
        field = indirect(field)

        start, end := r.start, r.or
        if end < 0 {
                end = r.end
        }
        if r.altstart >= 0 {
                end = r.altstart
        }
        first := true

        // Code common to all the loops.
        loopBody := func(newst *state) {
                // .alternates between elements
                if !first && r.altstart >= 0 {
                        for i := r.altstart; i < r.altend; {
                                i = t.executeElement(i, newst)
                        }
                }
                first = false
                for i := start; i < end; {
                        i = t.executeElement(i, newst)
                }
        }

        if array, ok := field.(reflect.ArrayOrSliceValue); ok {
                for j := 0; j < array.Len(); j++ {
                        loopBody(st.clone(array.Elem(j)))
                }
        } else if m, ok := field.(*reflect.MapValue); ok {
                for _, key := range m.Keys() {
                        loopBody(st.clone(m.Elem(key)))
                }
        } else if ch := iter(field); ch != nil {
                for {
                        e := ch.Recv()
                        if ch.Closed() {
                                break
                        }
                        loopBody(st.clone(e))
                }
        } else {
                t.execError(st, r.linenum, ".repeated: cannot repeat %s (type %s)",
                        r.field, field.Type())
        }

        if first {
                // Empty. Execute the .or block, once.  If it's missing, do nothing.
                start, end := r.or, r.end
                if start >= 0 {
                        newst := st.clone(field)
                        for i := start; i < end; {
                                i = t.executeElement(i, newst)
                        }
                }
                return
        }
}

// A valid delimiter must contain no white space and be non-empty.
func validDelim(d []byte) bool {
        if len(d) == 0 {
                return false
        }
        for _, c := range d {
                if white(c) {
                        return false
                }
        }
        return true
}

// checkError is a deferred function to turn a panic with type *Error into a plain error return.
// Other panics are unexpected and so are re-enabled.
func checkError(error *os.Error) {
        if v := recover(); v != nil {
                if e, ok := v.(*Error); ok {
                        *error = e
                } else {
                        // runtime errors should crash
                        panic(v)
                }
        }
}

// -- Public interface

// Parse initializes a Template by parsing its definition.  The string
// s contains the template text.  If any errors occur, Parse returns
// the error.
func (t *Template) Parse(s string) (err os.Error) {
        if t.elems == nil {
                return &Error{1, "template not allocated with New"}
        }
        if !validDelim(t.ldelim) || !validDelim(t.rdelim) {
                return &Error{1, fmt.Sprintf("bad delimiter strings %q %q", t.ldelim, t.rdelim)}
        }
        defer checkError(&err)
        t.buf = []byte(s)
        t.p = 0
        t.linenum = 1
        t.parse()
        return nil
}

// ParseFile is like Parse but reads the template definition from the
// named file.
func (t *Template) ParseFile(filename string) (err os.Error) {
        b, err := ioutil.ReadFile(filename)
        if err != nil {
                return err
        }
        return t.Parse(string(b))
}

// Execute applies a parsed template to the specified data object,
// generating output to wr.
func (t *Template) Execute(data interface{}, wr io.Writer) (err os.Error) {
        // Extract the driver data.
        val := reflect.NewValue(data)
        defer checkError(&err)
        t.p = 0
        t.execute(0, t.elems.Len(), &state{nil, val, wr})
        return nil
}

// SetDelims sets the left and right delimiters for operations in the
// template.  They are validated during parsing.  They could be
// validated here but it's better to keep the routine simple.  The
// delimiters are very rarely invalid and Parse has the necessary
// error-handling interface already.
func (t *Template) SetDelims(left, right string) {
        t.ldelim = []byte(left)
        t.rdelim = []byte(right)
}

// Parse creates a Template with default parameters (such as {} for
// metacharacters).  The string s contains the template text while
// the formatter map fmap, which may be nil, defines auxiliary functions
// for formatting variables.  The template is returned. If any errors
// occur, err will be non-nil.
func Parse(s string, fmap FormatterMap) (t *Template, err os.Error) {
        t = New(fmap)
        err = t.Parse(s)
        if err != nil {
                t = nil
        }
        return
}

// ParseFile is a wrapper function that creates a Template with default
// parameters (such as {} for metacharacters).  The filename identifies
// a file containing the template text, while the formatter map fmap, which
// may be nil, defines auxiliary functions for formatting variables.
// The template is returned. If any errors occur, err will be non-nil.
func ParseFile(filename string, fmap FormatterMap) (t *Template, err os.Error) {
        b, err := ioutil.ReadFile(filename)
        if err != nil {
                return nil, err
        }
        return Parse(string(b), fmap)
}

// MustParse is like Parse but panics if the template cannot be parsed.
func MustParse(s string, fmap FormatterMap) *Template {
        t, err := Parse(s, fmap)
        if err != nil {
                panic("template.MustParse error: " + err.String())
        }
        return t
}

// MustParseFile is like ParseFile but panics if the file cannot be read
// or the template cannot be parsed.
func MustParseFile(filename string, fmap FormatterMap) *Template {
        b, err := ioutil.ReadFile(filename)
        if err != nil {
                panic("template.MustParseFile error: " + err.String())
        }
        return MustParse(string(b), fmap)
}