Create quads hierarchy

* Move nquads into quad.
* Create cquads simplified parser in quad.
* Move Triple (renamed Quad) to quad.

Also made sure mongo actually implements BulkLoader.

quad/cquads/actions.rl

@@ -0,0 +1,95 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+%%{
+	machine quads;
+
+	action Escape {
+		isEscaped = true
+	}
+
+	action Quote {
+		isQuoted = true
+	}
+
+	action StartSubject {
+		subject = p
+	}
+
+	action StartPredicate {
+		predicate = p
+	}
+
+	action StartObject {
+		object = p
+	}
+
+	action StartLabel {
+		label = p
+	}
+
+	action SetSubject {
+		if subject < 0 {
+			panic("unexpected parser state: subject start not set")
+		}
+		q.Subject = unEscape(data[subject:p], isQuoted, isEscaped)
+		isEscaped = false
+		isQuoted = false
+	}
+
+	action SetPredicate {
+		if predicate < 0 {
+			panic("unexpected parser state: predicate start not set")
+		}
+		q.Predicate = unEscape(data[predicate:p], isQuoted, isEscaped)
+		isEscaped = false
+		isQuoted = false
+	}
+
+	action SetObject {
+		if object < 0 {
+			panic("unexpected parser state: object start not set")
+		}
+		q.Object = unEscape(data[object:p], isQuoted, isEscaped)
+		isEscaped = false
+		isQuoted = false
+	}
+
+	action SetLabel {
+		if label < 0 {
+			panic("unexpected parser state: label start not set")
+		}
+		q.Provenance = unEscape(data[label:p], isQuoted, isEscaped)
+		isEscaped = false
+		isQuoted = false
+	}
+
+	action Return {
+		return q, nil
+	}
+
+	action Comment {
+	}
+
+	action Error {
+		if p < len(data) {
+			if r := data[p]; r < unicode.MaxASCII {
+				return q, fmt.Errorf("%v: unexpected rune %q at %d", quad.ErrInvalid, data[p], p)
+			} else {
+				return q, fmt.Errorf("%v: unexpected rune %q (\\u%04x) at %d", quad.ErrInvalid, data[p], data[p], p)
+			}
+		}
+		return q, quad.ErrIncomplete
+	}
+}%%

quad/cquads/cquads.go

@@ -0,0 +1,141 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package cquads implements parsing N-Quads like line-based syntax
+// for RDF datasets.
+//
+// N-Quad parsing is performed as based on a simplified grammar derived from
+// the N-Quads grammar defined by http://www.w3.org/TR/n-quads/.
+//
+// For a complete definition of the grammar, see cquads.rl.
+package cquads
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/google/cayley/quad"
+)
+
+// Parse returns a valid quad.Quad or a non-nil error. Parse does
+// handle comments except where the comment placement does not prevent
+// a complete valid quad.Quad from being defined.
+func Parse(str string) (*quad.Quad, error) {
+	q, err := parse([]rune(str))
+	return &q, err
+}
+
+// Decoder implements simplified N-Quad document parsing.
+type Decoder struct {
+	r    *bufio.Reader
+	line []byte
+}
+
+// NewDecoder returns an N-Quad decoder that takes its input from the
+// provided io.Reader.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r: bufio.NewReader(r)}
+}
+
+// Unmarshal returns the next valid N-Quad as a quad.Quad, or an error.
+func (dec *Decoder) Unmarshal() (*quad.Quad, error) {
+	dec.line = dec.line[:0]
+	var line []byte
+	for {
+		for {
+			l, pre, err := dec.r.ReadLine()
+			if err != nil {
+				return nil, err
+			}
+			dec.line = append(dec.line, l...)
+			if !pre {
+				break
+			}
+		}
+		if line = bytes.TrimSpace(dec.line); len(line) != 0 && line[0] != '#' {
+			break
+		}
+		dec.line = dec.line[:0]
+	}
+	triple, err := Parse(string(line))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse %q: %v", dec.line, err)
+	}
+	if triple == nil {
+		return dec.Unmarshal()
+	}
+	return triple, nil
+}
+
+func unEscape(r []rune, isQuoted, isEscaped bool) string {
+	if isQuoted {
+		r = r[1 : len(r)-1]
+	}
+	if !isEscaped {
+		return string(r)
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 0, len(r)))
+
+	for i := 0; i < len(r); {
+		switch r[i] {
+		case '\\':
+			i++
+			var c byte
+			switch r[i] {
+			case 't':
+				c = '\t'
+			case 'b':
+				c = '\b'
+			case 'n':
+				c = '\n'
+			case 'r':
+				c = '\r'
+			case 'f':
+				c = '\f'
+			case '"':
+				c = '"'
+			case '\'':
+				c = '\''
+			case '\\':
+				c = '\\'
+			case 'u':
+				rc, err := strconv.ParseInt(string(r[i+1:i+5]), 16, 32)
+				if err != nil {
+					panic(fmt.Errorf("internal parser error: %v", err))
+				}
+				buf.WriteRune(rune(rc))
+				i += 5
+				continue
+			case 'U':
+				rc, err := strconv.ParseInt(string(r[i+1:i+9]), 16, 32)
+				if err != nil {
+					panic(fmt.Errorf("internal parser error: %v", err))
+				}
+				buf.WriteRune(rune(rc))
+				i += 9
+				continue
+			}
+			buf.WriteByte(c)
+		default:
+			buf.WriteRune(r[i])
+		}
+		i++
+	}
+
+	return buf.String()
+}

quad/cquads/cquads.rl

@@ -0,0 +1,106 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Ragel gramar definition derived from http://www.w3.org/TR/n-quads/#sec-grammar.
+
+%%{
+	machine quads;
+
+	alphtype rune;
+
+	PN_CHARS_BASE           = [A-Za-z]
+							| 0x00c0 .. 0x00d6
+							| 0x00d8 .. 0x00f6
+							| 0x00f8 .. 0x02ff
+							| 0x0370 .. 0x037d
+							| 0x037f .. 0x1fff
+							| 0x200c .. 0x200d
+							| 0x2070 .. 0x218f
+							| 0x2c00 .. 0x2fef
+							| 0x3001 .. 0xd7ff
+							| 0xf900 .. 0xfdcf
+							| 0xfdf0 .. 0xfffd
+							| 0x10000 .. 0xeffff
+							;
+
+	PN_CHARS_U              = PN_CHARS_BASE | '_' | ':' ;
+
+	PN_CHARS                = PN_CHARS_U
+							| '-'
+							| [0-9]
+							| 0xb7
+							| 0x0300 .. 0x036f
+							| 0x203f .. 0x2040
+							;
+
+	ECHAR                   = ('\\' [tbnrf"'\\]) %Escape ;
+
+	UCHAR                   = ('\\u' xdigit {4}
+							| '\\U' xdigit {8}) %Escape
+							;
+
+	BLANK_NODE_LABEL        = '_:' (PN_CHARS_U | [0-9]) ((PN_CHARS | '.')* PN_CHARS)? ;
+
+	STRING_LITERAL          = (
+							  '!'
+							| '#' .. '['
+							| ']' .. 0x7e
+							| 0x80 .. 0x10ffff
+							| ECHAR
+							| UCHAR)+ - ('_:' | any* '.' | '#' any*)
+							;
+
+	STRING_LITERAL_QUOTE    = '"' (
+							  0x00 .. 0x09
+							| 0x0b .. 0x0c
+							| 0x0e .. '!'
+							| '#' .. '['
+							| ']' .. 0x10ffff
+							| ECHAR
+							| UCHAR)*
+							  '"'
+							;
+
+	IRIREF                  = '<' (
+							  '!' .. ';'
+							| '='
+							| '?' .. '['
+							| ']'
+							| '_'
+							| 'a' .. 'z'
+							| '~'
+							| 0x80 .. 0x10ffff
+							| UCHAR)*
+							  '>'
+							;
+
+	LANGTAG                 = '@' [a-zA-Z]+ ('-' [a-zA-Z0-9]+)* ;
+
+	whitespace              = [ \t] ;
+
+	literal                 = STRING_LITERAL | STRING_LITERAL_QUOTE % Quote | STRING_LITERAL_QUOTE ('^^' IRIREF | LANGTAG) ;
+
+	subject                 = (literal | BLANK_NODE_LABEL) ;
+	predicate               = literal ;
+	object                  = (literal | BLANK_NODE_LABEL) ;
+	graphLabel              = (literal | BLANK_NODE_LABEL) ;
+
+	statement := (
+					whitespace*  subject    >StartSubject   %SetSubject
+					whitespace+  predicate  >StartPredicate %SetPredicate
+					whitespace+  object     >StartObject    %SetObject
+					(whitespace+ graphLabel >StartLabel     %SetLabel)?
+					whitespace*  '.' whitespace* ('#' any*)? >Comment
+				 ) %Return @!Error ;
+}%%

quad/cquads/parse.rl

@@ -0,0 +1,58 @@
+// GO SOURCE FILE MACHINE GENERATED BY RAGEL; DO NOT EDIT
+
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cquads
+
+import (
+	"fmt"
+	"unicode"
+
+	"github.com/google/cayley/quad"
+)
+
+%%{
+	machine quads;
+
+	include "actions.rl";
+
+	include "cquads.rl";
+
+	write data;
+}%%
+
+func parse(data []rune) (quad.Quad, error) {
+	var (
+		cs, p int
+		pe    = len(data)
+		eof   = pe
+
+		subject   = -1
+		predicate = -1
+		object    = -1
+		label     = -1
+
+		isEscaped bool
+		isQuoted  bool
+
+		q quad.Quad
+	)
+
+	%%write init;
+
+	%%write exec;
+
+	return quad.Quad{}, quad.ErrInvalid
+}

quad/nquads/actions.rl

@@ -0,0 +1,87 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+%%{
+	machine quads;
+
+	action Escape {
+		isEscaped = true
+	}
+
+	action StartSubject {
+		subject = p
+	}
+
+	action StartPredicate {
+		predicate = p
+	}
+
+	action StartObject {
+		object = p
+	}
+
+	action StartLabel {
+		label = p
+	}
+
+	action SetSubject {
+		if subject < 0 {
+			panic("unexpected parser state: subject start not set")
+		}
+		q.Subject = unEscape(data[subject:p], isEscaped)
+		isEscaped = false
+	}
+
+	action SetPredicate {
+		if predicate < 0 {
+			panic("unexpected parser state: predicate start not set")
+		}
+		q.Predicate = unEscape(data[predicate:p], isEscaped)
+		isEscaped = false
+	}
+
+	action SetObject {
+		if object < 0 {
+			panic("unexpected parser state: object start not set")
+		}
+		q.Object = unEscape(data[object:p], isEscaped)
+		isEscaped = false
+	}
+
+	action SetLabel {
+		if label < 0 {
+			panic("unexpected parser state: label start not set")
+		}
+		q.Provenance = unEscape(data[label:p], isEscaped)
+		isEscaped = false
+	}
+
+	action Return {
+		return q, nil
+	}
+
+	action Comment {
+	}
+
+	action Error {
+		if p < len(data) {
+			if r := data[p]; r < unicode.MaxASCII {
+				return q, fmt.Errorf("%v: unexpected rune %q at %d", quad.ErrInvalid, data[p], p)
+			} else {
+				return q, fmt.Errorf("%v: unexpected rune %q (\\u%04x) at %d", quad.ErrInvalid, data[p], data[p], p)
+			}
+		}
+		return q, quad.ErrIncomplete
+	}
+}%%

quad/nquads/nquads.go

@@ -0,0 +1,138 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package nquads implements parsing the RDF 1.1 N-Quads line-based syntax
+// for RDF datasets.
+//
+// N-Quad parsing is performed as defined by http://www.w3.org/TR/n-quads/
+// with the exception that the nquads package will allow relative IRI values,
+// which are prohibited by the N-Quads quad-Quads specifications.
+package nquads
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/google/cayley/quad"
+)
+
+// Parse returns a valid quad.Quad or a non-nil error. Parse does
+// handle comments except where the comment placement does not prevent
+// a complete valid quad.Quad from being defined.
+func Parse(str string) (*quad.Quad, error) {
+	q, err := parse([]rune(str))
+	return &q, err
+}
+
+// Decoder implements N-Quad document parsing according to the RDF
+// 1.1 N-Quads specification.
+type Decoder struct {
+	r    *bufio.Reader
+	line []byte
+}
+
+// NewDecoder returns an N-Quad decoder that takes its input from the
+// provided io.Reader.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r: bufio.NewReader(r)}
+}
+
+// Unmarshal returns the next valid N-Quad as a quad.Quad, or an error.
+func (dec *Decoder) Unmarshal() (*quad.Quad, error) {
+	dec.line = dec.line[:0]
+	var line []byte
+	for {
+		for {
+			l, pre, err := dec.r.ReadLine()
+			if err != nil {
+				return nil, err
+			}
+			dec.line = append(dec.line, l...)
+			if !pre {
+				break
+			}
+		}
+		if line = bytes.TrimSpace(dec.line); len(line) != 0 && line[0] != '#' {
+			break
+		}
+		dec.line = dec.line[:0]
+	}
+	triple, err := Parse(string(line))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse %q: %v", dec.line, err)
+	}
+	if triple == nil {
+		return dec.Unmarshal()
+	}
+	return triple, nil
+}
+
+func unEscape(r []rune, isEscaped bool) string {
+	if !isEscaped {
+		return string(r)
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 0, len(r)))
+
+	for i := 0; i < len(r); {
+		switch r[i] {
+		case '\\':
+			i++
+			var c byte
+			switch r[i] {
+			case 't':
+				c = '\t'
+			case 'b':
+				c = '\b'
+			case 'n':
+				c = '\n'
+			case 'r':
+				c = '\r'
+			case 'f':
+				c = '\f'
+			case '"':
+				c = '"'
+			case '\'':
+				c = '\''
+			case '\\':
+				c = '\\'
+			case 'u':
+				rc, err := strconv.ParseInt(string(r[i+1:i+5]), 16, 32)
+				if err != nil {
+					panic(fmt.Errorf("internal parser error: %v", err))
+				}
+				buf.WriteRune(rune(rc))
+				i += 5
+				continue
+			case 'U':
+				rc, err := strconv.ParseInt(string(r[i+1:i+9]), 16, 32)
+				if err != nil {
+					panic(fmt.Errorf("internal parser error: %v", err))
+				}
+				buf.WriteRune(rune(rc))
+				i += 9
+				continue
+			}
+			buf.WriteByte(c)
+		default:
+			buf.WriteRune(r[i])
+		}
+		i++
+	}
+
+	return buf.String()
+}

quad/nquads/nquads.rl

@@ -0,0 +1,97 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Ragel gramar definition derived from http://www.w3.org/TR/n-quads/#sec-grammar.
+
+%%{
+	machine quads;
+
+	alphtype rune;
+
+	PN_CHARS_BASE           = [A-Za-z]
+							| 0x00c0 .. 0x00d6
+							| 0x00d8 .. 0x00f6
+							| 0x00f8 .. 0x02ff
+							| 0x0370 .. 0x037d
+							| 0x037f .. 0x1fff
+							| 0x200c .. 0x200d
+							| 0x2070 .. 0x218f
+							| 0x2c00 .. 0x2fef
+							| 0x3001 .. 0xd7ff
+							| 0xf900 .. 0xfdcf
+							| 0xfdf0 .. 0xfffd
+							| 0x10000 .. 0xeffff
+							;
+
+	PN_CHARS_U              = PN_CHARS_BASE | '_' | ':' ;
+
+	PN_CHARS                = PN_CHARS_U
+							| '-'
+							| [0-9]
+							| 0xb7
+							| 0x0300 .. 0x036f
+							| 0x203f .. 0x2040
+							;
+
+	ECHAR                   = ('\\' [tbnrf"'\\]) %Escape ;
+
+	UCHAR                   = ('\\u' xdigit {4}
+							| '\\U' xdigit {8}) %Escape
+							;
+
+	BLANK_NODE_LABEL        = '_:' (PN_CHARS_U | [0-9]) ((PN_CHARS | '.')* PN_CHARS)? ;
+
+	STRING_LITERAL_QUOTE    = '"' (
+							  0x00 .. 0x09
+							| 0x0b .. 0x0c
+							| 0x0e .. '!'
+							| '#' .. '['
+							| ']' .. 0x10ffff
+							| ECHAR
+							| UCHAR)*
+							  '"'
+							;
+
+	IRIREF                  = '<' (
+							  '!' .. ';'
+							| '='
+							| '?' .. '['
+							| ']'
+							| '_'
+							| 'a' .. 'z'
+							| '~'
+							| 0x80 .. 0x10ffff
+							| UCHAR)*
+							  '>'
+							;
+
+	LANGTAG                 = '@' [a-zA-Z]+ ('-' [a-zA-Z0-9]+)* ;
+
+	whitespace              = [ \t] ;
+
+	literal                 = STRING_LITERAL_QUOTE ('^^' IRIREF | LANGTAG)? ;
+
+	subject                 = IRIREF | BLANK_NODE_LABEL ;
+	predicate               = IRIREF ;
+	object                  = IRIREF | BLANK_NODE_LABEL | literal ;
+	graphLabel              = IRIREF | BLANK_NODE_LABEL ;
+
+	statement := (
+					whitespace*  subject    >StartSubject   %SetSubject
+					whitespace*  predicate  >StartPredicate %SetPredicate
+					whitespace*  object     >StartObject    %SetObject
+					(whitespace* graphLabel >StartLabel     %SetLabel)?
+					whitespace*  '.' whitespace* ('#' any*)? >Comment
+				 ) %Return @!Error ;
+}%%

quad/nquads/parse.rl

@@ -0,0 +1,57 @@
+// GO SOURCE FILE MACHINE GENERATED BY RAGEL; DO NOT EDIT
+
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package nquads
+
+import (
+	"fmt"
+	"unicode"
+
+	"github.com/google/cayley/quad"
+)
+
+%%{
+	machine quads;
+
+	include "actions.rl";
+
+	include "nquads.rl";
+
+	write data;
+}%%
+
+func parse(data []rune) (quad.Quad, error) {
+	var (
+		cs, p int
+		pe    = len(data)
+		eof   = pe
+
+		subject   = -1
+		predicate = -1
+		object    = -1
+		label     = -1
+
+		isEscaped bool
+
+		q quad.Quad
+	)
+
+	%%write init;
+
+	%%write exec;
+
+	return quad.Quad{}, quad.ErrInvalid
+}

quad/nquads/quadfix.go

@@ -0,0 +1,226 @@
+// +build ignore
+
+package main
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/google/cayley/graph"
+)
+
+func main() {
+	dec := NewDecoder(os.Stdin)
+	for {
+		t, err := dec.Unmarshal()
+		if err != nil {
+			if err == io.EOF {
+				return
+			}
+			log.Println(err)
+		}
+		if t.Subject[0] == ':' && t.Subject[1] == '/' {
+			t.Subject = "<" + t.Subject[1:] + ">"
+		} else {
+			t.Subject = "_" + t.Subject
+		}
+		if t.Object[0] == ':' {
+			if t.Object[1] == '/' {
+				t.Object = "<" + t.Object[1:] + ">"
+			} else {
+				t.Object = "_" + t.Object
+			}
+		} else if t.Object[0] == '/' {
+			t.Object = "<" + t.Object + ">"
+		} else {
+			t.Object = fmt.Sprintf(`%q`, t.Object)
+		}
+		fmt.Printf("%s <%s> %s .\n", t.Subject, t.Predicate, t.Object)
+	}
+}
+
+// Historical N-Quads parser code.
+// -------------------------------
+
+var (
+	ErrAbsentSubject   = errors.New("nqauds: absent subject")
+	ErrAbsentPredicate = errors.New("nqauds: absent predicate")
+	ErrAbsentObject    = errors.New("nqauds: absent object")
+	ErrUnterminated    = errors.New("nqauds: unterminated quad")
+)
+
+func Parse(str string) (*graph.Triple, error) {
+	// Skip leading whitespace.
+	str = trimSpace(str)
+	// Check for a comment
+	if str != "" && str[0] == '#' {
+		return nil, nil
+	}
+	sub, remainder := getTripleComponent(str)
+	if sub == "" {
+		return nil, ErrAbsentSubject
+	}
+	str = trimSpace(remainder)
+	pred, remainder := getTripleComponent(str)
+	if pred == "" {
+		return nil, ErrAbsentPredicate
+	}
+	str = trimSpace(remainder)
+	obj, remainder := getTripleComponent(str)
+	if obj == "" {
+		return nil, ErrAbsentObject
+	}
+	str = trimSpace(remainder)
+	prov, remainder := getTripleComponent(str)
+	str = trimSpace(remainder)
+	if str != "" && str[0] == '.' {
+		return &graph.Triple{sub, pred, obj, prov}, nil
+	}
+	return nil, ErrUnterminated
+}
+
+func isSpace(s uint8) bool {
+	return s == ' ' || s == '\t' || s == '\r'
+}
+
+func trimSpace(str string) string {
+	i := 0
+	for i < len(str) && isSpace(str[i]) {
+		i += 1
+	}
+	return str[i:]
+}
+
+func getTripleComponent(str string) (head, tail string) {
+	if len(str) == 0 {
+		return "", str
+	}
+	if str[0] == '<' {
+		return getUriPart(str[1:])
+	} else if str[0] == '"' {
+		return getQuotedPart(str[1:])
+	} else if str[0] == '.' {
+		return "", str
+	} else {
+		// Technically not part of the spec. But we do it anyway for convenience.
+		return getUnquotedPart(str)
+	}
+}
+
+func getUriPart(str string) (head, tail string) {
+	i := 0
+	for i < len(str) && str[i] != '>' {
+		i += 1
+	}
+	if i == len(str) {
+		return "", str
+	}
+	head = str[0:i]
+	return head, str[i+1:]
+}
+
+func getQuotedPart(str string) (head, tail string) {
+	var (
+		i     int
+		start int
+	)
+	for i < len(str) && str[i] != '"' {
+		if str[i] == '\\' {
+			head += str[start:i]
+			switch str[i+1] {
+			case '\\':
+				head += "\\"
+			case 'r':
+				head += "\r"
+			case 'n':
+				head += "\n"
+			case 't':
+				head += "\t"
+			case '"':
+				head += "\""
+			default:
+				return "", str
+			}
+			i += 2
+			start = i
+			continue
+		}
+		i += 1
+	}
+	if i == len(str) {
+		return "", str
+	}
+	head += str[start:i]
+	i += 1
+	switch {
+	case strings.HasPrefix(str[i:], "^^<"):
+		// Ignore type, for now
+		_, tail = getUriPart(str[i+3:])
+	case str[i] == '@':
+		_, tail = getUnquotedPart(str[i+1:])
+	default:
+		tail = str[i:]
+	}
+
+	return head, tail
+}
+
+func getUnquotedPart(str string) (head, tail string) {
+	var (
+		i       int
+		initStr = str
+		start   int
+	)
+	for i < len(str) && !isSpace(str[i]) {
+		if str[i] == '"' {
+			part, remainder := getQuotedPart(str[i+1:])
+			if part == "" {
+				return part, initStr
+			}
+			head += str[start:i]
+			str = remainder
+			i = 0
+			start = 0
+			head += part
+		}
+		i += 1
+	}
+	head += str[start:i]
+	return head, str[i:]
+}
+
+type Decoder struct {
+	r    *bufio.Reader
+	line []byte
+}
+
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r: bufio.NewReader(r)}
+}
+
+func (dec *Decoder) Unmarshal() (*graph.Triple, error) {
+	dec.line = dec.line[:0]
+	for {
+		l, pre, err := dec.r.ReadLine()
+		if err != nil {
+			return nil, err
+		}
+		dec.line = append(dec.line, l...)
+		if !pre {
+			break
+		}
+	}
+	triple, err := Parse(string(dec.line))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse %q: %v", dec.line, err)
+	}
+	if triple == nil {
+		return dec.Unmarshal()
+	}
+	return triple, nil
+}

quad/quad.go

@@ -0,0 +1,152 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package quad defines quad and triple handling.
+package quad
+
+// Defines the struct which makes the TripleStore possible -- the triple.
+//
+// At its heart, it consists of three fields -- Subject, Predicate, and Object.
+// Three IDs that relate to each other. That's all there is to it. The triples
+// are the links in the graph, and the existence of node IDs is defined by the
+// fact that some triple in the graph mentions them.
+//
+// This means that a complete representation of the graph is equivalent to a
+// list of triples. The rest is just indexing for speed.
+//
+// Adding fields to the triple is not to be taken lightly. You'll see I mention
+// provenance, but don'q as yet use it in any backing store. In general, there
+// can be features that can be turned on or off for any store, but I haven'q
+// decided how to allow/disallow them yet. Another such example would be to add
+// a forward and reverse index field -- forward being "order the list of
+// objects pointed at by this subject with this predicate" such as first and
+// second children, top billing, what have you.
+//
+// There will never be that much in this file except for the definition, but
+// the consequences are not to be taken lightly. But do suggest cool features!
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrInvalid    = errors.New("invalid N-Quad")
+	ErrIncomplete = errors.New("incomplete N-Quad")
+)
+
+// Our triple struct, used throughout.
+type Quad struct {
+	Subject    string `json:"subject"`
+	Predicate  string `json:"predicate"`
+	Object     string `json:"object"`
+	Provenance string `json:"provenance,omitempty"`
+}
+
+// Direction specifies an edge's type.
+type Direction byte
+
+// List of the valid directions of a triple.
+const (
+	Any Direction = iota
+	Subject
+	Predicate
+	Object
+	Provenance
+)
+
+func (d Direction) Prefix() byte {
+	switch d {
+	case Any:
+		return 'a'
+	case Subject:
+		return 's'
+	case Predicate:
+		return 'p'
+	case Provenance:
+		return 'c'
+	case Object:
+		return 'o'
+	default:
+		return '\x00'
+	}
+}
+
+func (d Direction) String() string {
+	switch d {
+	case Any:
+		return "any"
+	case Subject:
+		return "subject"
+	case Predicate:
+		return "predicate"
+	case Provenance:
+		return "provenance"
+	case Object:
+		return "object"
+	default:
+		return fmt.Sprint("illegal direction:", byte(d))
+	}
+}
+
+// TODO(kortschak) Consider writing methods onto the concrete type
+// instead of the pointer. This needs benchmarking to make the decision.
+
+// Per-field accessor for triples
+func (q *Quad) Get(d Direction) string {
+	switch d {
+	case Subject:
+		return q.Subject
+	case Predicate:
+		return q.Predicate
+	case Provenance:
+		return q.Provenance
+	case Object:
+		return q.Object
+	default:
+		panic(d.String())
+	}
+}
+
+func (q *Quad) Equals(o *Quad) bool {
+	return *q == *o
+}
+
+// Pretty-prints a triple.
+func (q *Quad) String() string {
+	// TODO(kortschak) String methods should generally not terminate in '\n'.
+	return fmt.Sprintf("%s -- %s -> %s\n", q.Subject, q.Predicate, q.Object)
+}
+
+func (q *Quad) IsValid() bool {
+	return q.Subject != "" && q.Predicate != "" && q.Object != ""
+}
+
+// TODO(kortschak) NTriple looks like a good candidate for conversion
+// to MarshalText() (text []byte, err error) and then move parsing code
+// from nquads to here to provide UnmarshalText(text []byte) error.
+
+// Prints a triple in N-Quad format.
+func (q *Quad) NTriple() string {
+	if q.Provenance == "" {
+		//TODO(barakmich): Proper escaping.
+		return fmt.Sprintf("%s %s %s .", q.Subject, q.Predicate, q.Object)
+	} else {
+		return fmt.Sprintf("%s %s %s %s .", q.Subject, q.Predicate, q.Object, q.Provenance)
+	}
+}
+
+type Unmarshaler interface {
+	Unmarshal() (*Quad, error)
+}