From 68cde88125e1f016c5706ca8d0b3db6ba06624a2 Mon Sep 17 00:00:00 2001
From: Adam Scarr <adam@vektah.net>
Date: Sun, 6 Aug 2017 14:31:35 +1000
Subject: [PATCH] Initial commit

---
 .editorconfig      |   9 ++
 .gitignore         |   2 +
 combinator.go      | 114 ++++++++++++++++++++++++
 combinator_test.go | 215 +++++++++++++++++++++++++++++++++++++++++++++
 examples/html.go   |  35 ++++++++
 nodes.go           |  43 +++++++++
 parser.go          | 122 +++++++++++++++++++++++++
 parser_test.go     | 107 ++++++++++++++++++++++
 pointer.go         |  81 +++++++++++++++++
 pointer_test.go    |  86 ++++++++++++++++++
 10 files changed, 814 insertions(+)
 create mode 100644 .editorconfig
 create mode 100644 .gitignore
 create mode 100644 combinator.go
 create mode 100644 combinator_test.go
 create mode 100644 examples/html.go
 create mode 100644 nodes.go
 create mode 100644 parser.go
 create mode 100644 parser_test.go
 create mode 100644 pointer.go
 create mode 100644 pointer_test.go

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..eef10cc
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,9 @@
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true
+
+[*.go]
+indent_style = tab
+indent_size = 4
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..29b636a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.idea
+*.iml
\ No newline at end of file
diff --git a/combinator.go b/combinator.go
new file mode 100644
index 0000000..2b6b8a3
--- /dev/null
+++ b/combinator.go
@@ -0,0 +1,114 @@
+package parsec
+
+func Nil(p Pointer) (Node, Pointer) {
+	return nil, p
+}
+
+func Never(p Pointer) (Node, Pointer) {
+	return Error{p.pos, "Never matches"}, p
+}
+
+func And(parsers ...Parserish) Parser {
+	if len(parsers) == 0 {
+		return Nil
+	}
+
+	ps := ParsifyAll(parsers...)
+
+	return func(p Pointer) (Node, Pointer) {
+		var nodes = make([]Node, 0, len(ps))
+		var node Node
+		newP := p
+		for _, parser := range ps {
+			node, newP = parser(newP)
+			if node == nil {
+				continue
+			}
+			if IsError(node) {
+				return node, p
+			}
+			nodes = append(nodes, node)
+		}
+		return NewSequence(p.pos, nodes...), newP
+	}
+}
+
+func Any(parsers ...Parserish) Parser {
+	if len(parsers) == 0 {
+		return Nil
+	}
+
+	ps := ParsifyAll(parsers...)
+
+	return func(p Pointer) (Node, Pointer) {
+		errors := []Error{}
+		for _, parser := range ps {
+			node, newP := parser(p)
+			if err, isErr := node.(Error); isErr {
+				errors = append(errors, err)
+				continue
+			}
+			return node, newP
+		}
+
+		longestError := errors[0]
+		for _, e := range errors[1:] {
+			if e.pos > longestError.pos {
+				longestError = e
+			}
+		}
+
+		return longestError, p
+	}
+}
+
+func Kleene(opScan Parserish, sepScan ...Parserish) Parser {
+	return manyImpl(0, opScan, Never, sepScan...)
+}
+
+func KleeneUntil(opScan Parserish, untilScan Parserish, sepScan ...Parserish) Parser {
+	return manyImpl(0, opScan, untilScan, sepScan...)
+}
+
+func Many(opScan Parserish, sepScan ...Parserish) Parser {
+	return manyImpl(1, opScan, Never, sepScan...)
+}
+
+func ManyUntil(opScan Parserish, untilScan Parserish, sepScan ...Parserish) Parser {
+	return manyImpl(1, opScan, untilScan, sepScan...)
+}
+
+func manyImpl(min int, op Parserish, until Parserish, sep ...Parserish) Parser {
+	opParser := Parsify(op)
+	untilParser := Parsify(until)
+	sepParser := Nil
+	if len(sep) > 0 {
+		sepParser = Parsify(sep[0])
+	}
+
+	return func(p Pointer) (Node, Pointer) {
+		var node Node
+		nodes := make([]Node, 0)
+		newP := p
+		for {
+			if node, _ := untilParser(newP); !IsError(node) {
+				if len(nodes) < min {
+					return NewError(newP.pos, "Unexpected input"), p
+				}
+				break
+			}
+
+			if node, newP = opParser(newP); IsError(node) {
+				if len(nodes) < min {
+					return node, p
+				}
+				break
+			}
+			nodes = append(nodes, node)
+			if node, newP = sepParser(newP); IsError(node) {
+				break
+			}
+		}
+		return NewSequence(p.pos, nodes...), newP
+	}
+}
diff --git a/combinator_test.go b/combinator_test.go
new file mode 100644
index 0000000..8c0bab0
--- /dev/null
+++ b/combinator_test.go
@@ -0,0 +1,215 @@
+package parsec
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNil(t *testing.T) {
+	p := Pointer{"hello world", 0}
+
+	node, p2 := Nil(p)
+	require.Equal(t, nil, node)
+	require.Equal(t, p, p2)
+}
+
+func TestAnd(t *testing.T) {
+	p := Pointer{"hello world", 0}
+
+	t.Run("matches sequence", func(t *testing.T) {
+		node, p2 := And("hello", WS, "world")(p)
+		require.Equal(t, NewSequence(0, NewToken(0, "hello"), NewToken(6, "world")), node)
+		require.Equal(t, 0, p2.Remaining())
+	})
+
+	t.Run("returns errors", func(t *testing.T) {
+		e, p3 := And("hello", WS, "there")(p)
+		require.Equal(t, NewError(6, "Expected there"), e)
+		require.Equal(t, 0, p3.pos)
+	})
+
+	t.Run("No parsers", func(t *testing.T) {
+		assertNilParser(t, And())
+	})
+}
+
+func TestAny(t *testing.T) {
+	p := Pointer{"hello world!", 0}
+
+	t.Run("Matches any", func(t *testing.T) {
+		node, p2 := Any("hello", "world")(p)
+		require.Equal(t, NewToken(0, "hello"), node)
+		require.Equal(t, 5, p2.pos)
+	})
+
+	t.Run("Returns longest error", func(t *testing.T) {
+		err, p2 := Any(
+			Exact("nope"),
+			And(Exact("hello"), WS, Exact("world"), Exact(".")),
+			And(Exact("hello"), WS, Exact("brother")),
+		)(p)
+		require.Equal(t, NewError(11, "Expected ."), err)
+		require.Equal(t, 0, p2.pos)
+	})
+
+	t.Run("Accepts nil matches", func(t *testing.T) {
+		node, p2 := Any(Exact("ffffff"), WS)(p)
+		require.Equal(t, nil, node)
+		require.Equal(t, 0, p2.pos)
+	})
+
+	t.Run("No parsers", func(t *testing.T) {
+		assertNilParser(t, Any())
+	})
+}
+
+func TestKleene(t *testing.T) {
+	p := Pointer{"a,b,c,d,e,", 0}
+
+	t.Run("Matches sequence with sep", func(t *testing.T) {
+		node, p2 := Kleene(CharRun("abcdefg"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+			NewToken(6, "d"),
+			NewToken(8, "e"),
+		), node)
+		require.Equal(t, 10, p2.pos)
+	})
+
+	t.Run("Matches sequence without sep", func(t *testing.T) {
+		node, p2 := Kleene(Any(CharRun("abcdefg"), Exact(",")))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(1, ","),
+			NewToken(2, "b"),
+			NewToken(3, ","),
+			NewToken(4, "c"),
+			NewToken(5, ","),
+			NewToken(6, "d"),
+			NewToken(7, ","),
+			NewToken(8, "e"),
+			NewToken(9, ","),
+		), node)
+		require.Equal(t, 10, p2.pos)
+	})
+
+	t.Run("Stops on error", func(t *testing.T) {
+		node, p2 := Kleene(CharRun("abc"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+		), node)
+		require.Equal(t, 6, p2.pos)
+		require.Equal(t, "d,e,", p2.Get())
+	})
+}
+
+func TestMany(t *testing.T) {
+	p := Pointer{"a,b,c,d,e,", 0}
+
+	t.Run("Matches sequence with sep", func(t *testing.T) {
+		node, p2 := Many(CharRun("abcdefg"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+			NewToken(6, "d"),
+			NewToken(8, "e"),
+		), node)
+		require.Equal(t, 10, p2.pos)
+	})
+
+	t.Run("Matches sequence without sep", func(t *testing.T) {
+		node, p2 := Many(Any(CharRun("abcdefg"), Exact(",")))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(1, ","),
+			NewToken(2, "b"),
+			NewToken(3, ","),
+			NewToken(4, "c"),
+			NewToken(5, ","),
+			NewToken(6, "d"),
+			NewToken(7, ","),
+			NewToken(8, "e"),
+			NewToken(9, ","),
+		), node)
+		require.Equal(t, 10, p2.pos)
+	})
+
+	t.Run("Stops on error", func(t *testing.T) {
+		node, p2 := Many(CharRun("abc"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+		), node)
+		require.Equal(t, 6, p2.pos)
+		require.Equal(t, "d,e,", p2.Get())
+	})
+
+	t.Run("Returns error if nothing matches", func(t *testing.T) {
+		node, p2 := Many(CharRun("def"), Exact(","))(p)
+		require.Equal(t, NewError(0, "Expected some of def"), node)
+		require.Equal(t, 0, p2.pos)
+		require.Equal(t, "a,b,c,d,e,", p2.Get())
+	})
+}
+
+func TestKleeneUntil(t *testing.T) {
+	p := Pointer{"a,b,c,d,e,fg", 0}
+
+	t.Run("Matches sequence with sep", func(t *testing.T) {
+		node, p2 := KleeneUntil(CharRun("abcde"), CharRun("d"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+		), node)
+		require.Equal(t, 6, p2.pos)
+	})
+
+	t.Run("Breaks if separator does not match", func(t *testing.T) {
+		node, p2 := KleeneUntil(Char("abcdefg"), Char("y"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+			NewToken(6, "d"),
+			NewToken(8, "e"),
+			NewToken(10, "f"),
+		), node)
+		require.Equal(t, 11, p2.pos)
+	})
+}
+
+func TestManyUntil(t *testing.T) {
+	p := Pointer{"a,b,c,d,e,", 0}
+
+	t.Run("Matches sequence until", func(t *testing.T) {
+		node, p2 := ManyUntil(CharRun("abcdefg"), Char("d"), Exact(","))(p)
+		require.Equal(t, NewSequence(0,
+			NewToken(0, "a"),
+			NewToken(2, "b"),
+			NewToken(4, "c"),
+		), node)
+		require.Equal(t, 6, p2.pos)
+	})
+
+	t.Run("Returns error until matches early", func(t *testing.T) {
+		node, p2 := ManyUntil(CharRun("abc"), Exact("a"), Exact(","))(p)
+		require.Equal(t, NewError(0, "Unexpected input"), node)
+		require.Equal(t, 0, p2.pos)
+		require.Equal(t, "a,b,c,d,e,", p2.Get())
+	})
+}
+
+func assertNilParser(t *testing.T, parser Parser) {
+	p := Pointer{"fff", 0}
+	node, p2 := parser(p)
+	require.Equal(t, nil, node)
+	require.Equal(t, p, p2)
+}
diff --git a/examples/html.go b/examples/html.go
new file mode 100644
index 0000000..88a3913
--- /dev/null
+++ b/examples/html.go
@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+
+	. "github.com/vektah/goparsify"
+)
+
+func html(p Pointer) (Node, Pointer) {
+	opentag := Exact("<")
+	closetag := Exact(">")
+	equal := Exact("=")
+	slash := Exact("/")
+	identifier := And(Char(Range("a-z")), CharRun(Range("a-zA-Z0-9")))
+	text := CharRunUntil("<>")
+
+	var tag Parser
+
+	element := Any(text, &tag)
+	elements := Kleene(element)
+	//attr := And(identifier, equal, String())
+	attr := And(identifier, equal, Exact(`"test"`))
+	attrws := And(attr, WS)
+	attrs := Kleene(attrws)
+	tstart := And(opentag, identifier, attrs, closetag)
+	tend := And(opentag, slash, identifier, closetag)
+	tag = And(tstart, elements, tend)
+
+	return element(p)
+}
+
+func main() {
+	node, _ := html(Input("<h1>hello world</h1>"))
+	fmt.Printf("%#v\n", node)
+}
diff --git a/nodes.go b/nodes.go
new file mode 100644
index 0000000..c51db6f
--- /dev/null
+++ b/nodes.go
@@ -0,0 +1,43 @@
+package parsec
+
+type Node interface {
+	Pos() int
+}
+
+type Token struct {
+	pos   int
+	Value string
+}
+
+func (e Token) Pos() int { return e.pos }
+
+func NewToken(pos int, value string) Token {
+	return Token{pos, value}
+}
+
+type Error struct {
+	pos   int
+	Error string
+}
+
+func (e Error) Pos() int { return e.pos }
+
+func NewError(pos int, message string) Error {
+	return Error{pos, message}
+}
+
+func IsError(n Node) bool {
+	_, isErr := n.(Error)
+	return isErr
+}
+
+type Sequence struct {
+	pos   int
+	Nodes []Node
+}
+
+func (e Sequence) Pos() int { return e.pos }
+
+func NewSequence(pos int, n ...Node) Sequence {
+	return Sequence{pos, n}
+}
diff --git a/parser.go b/parser.go
new file mode 100644
index 0000000..8066526
--- /dev/null
+++ b/parser.go
@@ -0,0 +1,122 @@
+package parsec
+
+import (
+	"fmt"
+)
+
+type Parser func(Pointer) (Node, Pointer)
+
+// Parserish types are any type that can be turned into a Parser by Parsify
+// These currently include *Parser and string literals.
+//
+// This makes recursive grammars cleaner and allows string literals to be used directly in most contexts.
+// eg, matching balanced paren:
+// ```go
+// var group Parser
+// group = And("(", Maybe(&group), ")")
+// ```
+// vs
+// ```go
+// var group ParserPtr{}
+// group.P = And(Exact("("), Maybe(group.Parse), Exact(")"))
+// ```
+type Parserish interface{}
+
+func Parsify(p Parserish) Parser {
+	switch p := p.(type) {
+	case func(Pointer) (Node, Pointer):
+		return Parser(p)
+	case Parser:
+		return p
+	case *Parser:
+		// Todo: Maybe capture this stack and on nil show it? Is there a good error library to do this?
+		return func(ptr Pointer) (Node, Pointer) {
+			return (*p)(ptr)
+		}
+	case string:
+		return Exact(p)
+	default:
+		panic(fmt.Errorf("cant turn a `%T` into a parser", p))
+	}
+}
+
+func ParsifyAll(parsers ...Parserish) []Parser {
+	ret := make([]Parser, len(parsers))
+	for i, parser := range parsers {
+		ret[i] = Parsify(parser)
+	}
+	return ret
+}
+
+func Exact(match string) Parser {
+	return func(p Pointer) (Node, Pointer) {
+		if !p.HasPrefix(match) {
+			return NewError(p.pos, "Expected "+match), p
+		}
+
+		return NewToken(p.pos, match), p.Advance(len(match))
+	}
+}
+
+func Char(match string) Parser {
+	return func(p Pointer) (Node, Pointer) {
+		r, p2 := p.Accept(match)
+		if r == "" {
+			return NewError(p.pos, "Expected one of "+string(match)), p
+		}
+
+		return NewToken(p.pos, string(r)), p2
+	}
+}
+
+func CharRun(match string) Parser {
+	return func(p Pointer) (Node, Pointer) {
+		s, p2 := p.AcceptRun(match)
+		if s == "" {
+			return NewError(p.pos, "Expected some of "+match), p
+		}
+
+		return NewToken(p.pos, s), p2
+	}
+}
+
+func CharRunUntil(match string) Parser {
+	return func(p Pointer) (Node, Pointer) {
+		s, p2 := p.AcceptUntil(match)
+		if s == "" {
+			return NewError(p.pos, "Expected some of "+match), p
+		}
+
+		return NewToken(p.pos, s), p2
+	}
+}
+
+func Range(r string) string {
+	runes := []rune(r)
+	if len(runes)%3 != 0 {
+		panic("ranges should be in the form a-z0-9")
+	}
+
+	match := ""
+
+	for i := 0; i < len(runes); i += 3 {
+		start := runes[i]
+		end := runes[i+2]
+		if start > end {
+			tmp := start
+			start = end
+			end = tmp
+		}
+		for c := start; c <= end; c++ {
+			match += string(c)
+		}
+	}
+
+	return match
+}
+
+func WS(p Pointer) (Node, Pointer) {
+	_, p2 := p.AcceptRun("\t\n\v\f\r \x85\xA0")
+
+	return nil, p2
+}
diff --git a/parser_test.go b/parser_test.go
new file mode 100644
index 0000000..7c22a76
--- /dev/null
+++ b/parser_test.go
@@ -0,0 +1,107 @@
+package parsec
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParsify(t *testing.T) {
+	p := Pointer{"ffooo", 0}
+
+	t.Run("strings", func(t *testing.T) {
+		node, _ := Parsify("ff")(p)
+		require.Equal(t, NewToken(0, "ff"), node)
+	})
+
+	t.Run("parsers", func(t *testing.T) {
+		node, _ := Parsify(CharRun("f"))(p)
+		require.Equal(t, NewToken(0, "ff"), node)
+	})
+
+	t.Run("*parsers", func(t *testing.T) {
+		var parser Parser
+		parserfied := Parsify(&parser)
+		parser = CharRun("f")
+
+		node, _ := parserfied(p)
+		require.Equal(t, NewToken(0, "ff"), node)
+	})
+}
+
+func TestExact(t *testing.T) {
+	p := Pointer{"fooo", 0}
+
+	t.Run("success", func(t *testing.T) {
+		node, p2 := Exact("fo")(p)
+		require.Equal(t, NewToken(0, "fo"), node)
+		require.Equal(t, p.Advance(2), p2)
+	})
+
+	t.Run("error", func(t *testing.T) {
+		node, p2 := Exact("bar")(p)
+		require.Equal(t, NewError(0, "Expected bar"), node)
+		require.Equal(t, 0, p2.pos)
+	})
+}
+
+func TestChar(t *testing.T) {
+	p := Pointer{"foobar", 0}
+
+	t.Run("success", func(t *testing.T) {
+		node, p2 := Char("fo")(p)
+		require.Equal(t, NewToken(0, "f"), node)
+		require.Equal(t, p.Advance(1), p2)
+	})
+
+	t.Run("error", func(t *testing.T) {
+		node, p2 := Char("bar")(p)
+		require.Equal(t, NewError(0, "Expected one of bar"), node)
+		require.Equal(t, 0, p2.pos)
+	})
+}
+
+func TestCharRun(t *testing.T) {
+	p := Pointer{"foobar", 0}
+
+	t.Run("success", func(t *testing.T) {
+		node, p2 := CharRun("fo")(p)
+		require.Equal(t, NewToken(0, "foo"), node)
+		require.Equal(t, p.Advance(3), p2)
+	})
+
+	t.Run("error", func(t *testing.T) {
+		node, p2 := CharRun("bar")(p)
+		require.Equal(t, NewError(0, "Expected some of bar"), node)
+		require.Equal(t, 0, p2.pos)
+	})
+}
+
+func TestCharUntil(t *testing.T) {
+	p := Pointer{"foobar", 0}
+
+	t.Run("success", func(t *testing.T) {
+		node, p2 := CharRunUntil("z")(p)
+		require.Equal(t, NewToken(0, "foobar"), node)
+		require.Equal(t, p.Advance(6), p2)
+	})
+
+	t.Run("error", func(t *testing.T) {
+		node, p2 := CharRunUntil("f")(p)
+		require.Equal(t, NewError(0, "Expected some of f"), node)
+		require.Equal(t, 0, p2.pos)
+	})
+}
+
+func TestWS(t *testing.T) {
+	p := Pointer{"  fooo", 0}
+
+	node, p2 := WS(p)
+	require.Equal(t, nil, node)
+	require.Equal(t, p.Advance(2), p2)
+}
+
+func TestRange(t *testing.T) {
+	require.Equal(t, "abcdefg", Range("a-g"))
+	require.Equal(t, "01234abcd", Range("0-4a-d"))
+}
diff --git a/pointer.go b/pointer.go
new file mode 100644
index 0000000..92b2bcb
--- /dev/null
+++ b/pointer.go
@@ -0,0 +1,81 @@
+package parsec
+
+import (
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	EOF rune = -1
+)
+
+func Input(s string) Pointer {
+	return Pointer{s, 0}
+}
+
+type Pointer struct {
+	input string
+	pos   int
+}
+
+func (p Pointer) Advance(i int) Pointer {
+	return Pointer{p.input, p.pos + i}
+}
+
+func (p Pointer) Get() string {
+	return p.input[p.pos:]
+}
+
+func (p Pointer) Remaining() int {
+	remaining := len(p.input) - p.pos
+	if remaining < 0 {
+		return 0
+	}
+	return remaining
+}
+
+func (p Pointer) Next() (rune, Pointer) {
+	if int(p.pos) >= len(p.input) {
+		return EOF, p
+	}
+	r, w := utf8.DecodeRuneInString(p.input[p.pos:])
+	return r, p.Advance(w)
+}
+
+func (p Pointer) HasPrefix(s string) bool {
+	return strings.HasPrefix(p.input[p.pos:], s)
+}
+
+func (p Pointer) Accept(valid string) (string, Pointer) {
+	c, newP := p.Next()
+	if strings.ContainsRune(valid, c) {
+		return string(c), newP
+	}
+	return "", p
+}
+
+func (p Pointer) AcceptRun(valid string) (string, Pointer) {
+	matched := 0
+	for p.pos+matched < len(p.input) {
+		r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
+		if !strings.ContainsRune(valid, r) {
+			break
+		}
+		matched += w
+	}
+
+	return p.input[p.pos : p.pos+matched], p.Advance(matched)
+}
+
+func (p Pointer) AcceptUntil(invalid string) (string, Pointer) {
+	matched := 0
+	for p.pos+matched < len(p.input) {
+		r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
+		if strings.ContainsRune(invalid, r) {
+			break
+		}
+		matched += w
+	}
+
+	return p.input[p.pos : p.pos+matched], p.Advance(matched)
+}
diff --git a/pointer_test.go b/pointer_test.go
new file mode 100644
index 0000000..e8076d7
--- /dev/null
+++ b/pointer_test.go
@@ -0,0 +1,86 @@
+package parsec
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPointer(t *testing.T) {
+	p := Pointer{"fooo", 0}
+
+	t.Run("Advances", func(t *testing.T) {
+		p2 := p.Advance(2)
+		require.Equal(t, Pointer{"fooo", 2}, p2)
+		require.Equal(t, Pointer{"fooo", 0}, p)
+		require.Equal(t, Pointer{"fooo", 3}, p2.Advance(1))
+	})
+
+	t.Run("Get", func(t *testing.T) {
+		require.Equal(t, "fooo", p.Get())
+		require.Equal(t, "ooo", p.Advance(1).Get())
+	})
+
+	t.Run("Remaining", func(t *testing.T) {
+		require.Equal(t, 4, p.Remaining())
+		require.Equal(t, 0, p.Advance(4).Remaining())
+		require.Equal(t, 0, p.Advance(10).Remaining())
+	})
+
+	t.Run("Next takes one character", func(t *testing.T) {
+		s, p2 := p.Next()
+		require.Equal(t, p.Advance(1), p2)
+		require.Equal(t, 'f', s)
+	})
+
+	t.Run("Next handles EOF", func(t *testing.T) {
+		s, p2 := p.Advance(5).Next()
+		require.Equal(t, p.Advance(5), p2)
+		require.Equal(t, EOF, s)
+	})
+
+	t.Run("HasPrefix", func(t *testing.T) {
+		require.True(t, p.HasPrefix("fo"))
+		require.False(t, p.HasPrefix("ooo"))
+		require.True(t, p.Advance(1).HasPrefix("ooo"))
+		require.False(t, p.Advance(1).HasPrefix("oooo"))
+	})
+
+	t.Run("Accept", func(t *testing.T) {
+		s, p2 := p.Accept("abcdef")
+		require.Equal(t, "f", s)
+		require.Equal(t, p.Advance(1), p2)
+
+		s, p2 = p.Accept("ooooo")
+		require.Equal(t, "", s)
+		require.Equal(t, p.Advance(0), p2)
+
+		s, p2 = p.Advance(4).Accept("ooooo")
+		require.Equal(t, "", s)
+		require.Equal(t, p.Advance(4), p2)
+	})
+
+	t.Run("AcceptRun", func(t *testing.T) {
+		s, p2 := p.AcceptRun("f")
+		require.Equal(t, "f", s)
+		require.Equal(t, p.Advance(1), p2)
+
+		s, p3 := p.AcceptRun("fo")
+		require.Equal(t, "fooo", s)
+		require.Equal(t, p.Advance(4), p3)
+
+		s, p4 := p3.AcceptRun("fo")
+		require.Equal(t, "", s)
+		require.Equal(t, p.Advance(4), p4)
+	})
+
+	t.Run("AcceptUntil", func(t *testing.T) {
+		s, p2 := p.AcceptUntil("o")
+		require.Equal(t, "f", s)
+		require.Equal(t, p.Advance(1), p2)
+
+		s, p3 := p2.AcceptRun("o")
+		require.Equal(t, "ooo", s)
+		require.Equal(t, p.Advance(4), p3)
+	})
+}