From 708052ec0a6bacf41702b41c7ccfb22a46bf959e Mon Sep 17 00:00:00 2001
From: surdeus <surdeus@gmail.com>
Date: Fri, 27 Jan 2023 22:05:46 +0500
Subject: [PATCH] Includes mk now.

---
 readme                 |   6 +
 src/cmd/goblin/main.go |   2 +
 src/tool/mk/expand.go  | 328 ++++++++++++++++++++++++++++++++
 src/tool/mk/graph.go   | 371 ++++++++++++++++++++++++++++++++++++
 src/tool/mk/lex.go     | 409 ++++++++++++++++++++++++++++++++++++++++
 src/tool/mk/main.go    | 417 +++++++++++++++++++++++++++++++++++++++++
 src/tool/mk/parse.go   | 384 +++++++++++++++++++++++++++++++++++++
 src/tool/mk/recipe.go  | 208 ++++++++++++++++++++
 src/tool/mk/rules.go   | 215 +++++++++++++++++++++
 9 files changed, 2340 insertions(+)
 create mode 100644 src/tool/mk/expand.go
 create mode 100644 src/tool/mk/graph.go
 create mode 100644 src/tool/mk/lex.go
 create mode 100644 src/tool/mk/main.go
 create mode 100644 src/tool/mk/parse.go
 create mode 100644 src/tool/mk/recipe.go
 create mode 100644 src/tool/mk/rules.go

diff --git a/readme b/readme
index b5d5644..0fa33ee 100644
--- a/readme
+++ b/readme
@@ -11,3 +11,9 @@ Inspired by Plan9, Suckless and cat-v software.
 Not Posix compatible since it's implemented thousand times.
 Lack of a few features is a feature too.
 
+Since Golang is so good at static files it makes sense to
+put many programs into one, so now it is gonna include many
+suckless stuff, including:
+
+	mk
+
diff --git a/src/cmd/goblin/main.go b/src/cmd/goblin/main.go
index 838fa1f..95d373d 100644
--- a/src/cmd/goblin/main.go
+++ b/src/cmd/goblin/main.go
@@ -26,6 +26,7 @@ import(
 	"github.com/surdeus/goblin/src/tool/in"
 	"github.com/surdeus/goblin/src/tool/useprog"
 	"github.com/surdeus/goblin/src/tool/path"
+	"github.com/surdeus/goblin/src/tool/mk"
 )
 
 func main() {
@@ -54,6 +55,7 @@ func main() {
 		"in" : mtool.Tool{in.Run, "filter strings from stdin that aren not in arguments"},
 		"useprog" : mtool.Tool{useprog.Run, "print the name of the first existing program in arg list"},
 		"path" : mtool.Tool{path.Run, "print cross platform path based on cmd arguments"},
+		"mk" : mtool.Tool{mk.Run, "file dependency system"},
 	}
 
 	mtool.Main("goblin", tools)
diff --git a/src/tool/mk/expand.go b/src/tool/mk/expand.go
new file mode 100644
index 0000000..8bbe6dc
--- /dev/null
+++ b/src/tool/mk/expand.go
@@ -0,0 +1,328 @@
+// String substitution and expansion.
+
+package mk
+
+import (
+	"regexp"
+	"strings"
+	"unicode/utf8"
+	"os"
+)
+
+// Expand a word. This includes substituting variables and handling quotes.
+func expand(input string, vars map[string][]string, expandBackticks bool) []string {
+	parts := make([]string, 0)
+	expanded := ""
+	var i, j int
+	for i = 0; i < len(input); {
+		j = strings.IndexAny(input[i:], "\"'`$\\")
+
+		if j < 0 {
+			expanded += input[i:]
+			break
+		}
+		j += i
+
+		expanded += input[i:j]
+		c, w := utf8.DecodeRuneInString(input[j:])
+		i = j + w
+
+		var off int
+		var out string
+		switch c {
+		case '\\':
+			out, off = expandEscape(input[i:])
+			expanded += out
+
+		case '"':
+			out, off = expandDoubleQuoted(input[i:], vars, expandBackticks)
+			expanded += out
+
+		case '\'':
+			out, off = expandSingleQuoted(input[i:])
+			expanded += out
+
+		case '`':
+			if expandBackticks {
+				var outparts []string
+				outparts, off = expandBackQuoted(input[i:], vars)
+				if len(outparts) > 0 {
+					outparts[0] = expanded + outparts[0]
+					expanded = outparts[len(outparts)-1]
+					parts = append(parts, outparts[:len(outparts)-1]...)
+				}
+			} else {
+				out = input
+				off = len(input)
+				expanded += out
+			}
+
+		case '$':
+			var outparts []string
+			outparts, off = expandSigil(input[i:], vars)
+			if len(outparts) > 0 {
+				firstpart := expanded + outparts[0]
+				if len(outparts) > 1 {
+					parts = append(parts, firstpart)
+					if len(outparts) > 2 {
+						parts = append(parts, outparts[1:len(outparts)-1]...)
+					}
+					expanded = outparts[len(outparts)-1]
+				} else {
+					expanded = firstpart
+				}
+			}
+		}
+
+		i += off
+	}
+
+	if len(expanded) > 0 {
+		parts = append(parts, expanded)
+	}
+
+	return parts
+}
+
+// Expand following a '\\'
+func expandEscape(input string) (string, int) {
+	c, w := utf8.DecodeRuneInString(input)
+	if c == '\t' || c == ' ' {
+		return string(c), w
+	}
+	return "\\" + string(c), w
+}
+
+// Expand a double quoted string starting after a '\"'
+func expandDoubleQuoted(input string, vars map[string][]string, expandBackticks bool) (string, int) {
+	// find the first non-escaped "
+	j := 0
+	for {
+		j = strings.IndexAny(input[j:], "\"\\")
+		if j < 0 {
+			break
+		}
+
+		c, w := utf8.DecodeRuneInString(input[j:])
+		j += w
+
+		if c == '"' {
+			return strings.Join(expand(input[:j], vars, expandBackticks), " "), (j + w)
+		}
+
+		if c == '\\' {
+			if j+w < len(input) {
+				j += w
+				_, w := utf8.DecodeRuneInString(input[j:])
+				j += w
+			} else {
+				break
+			}
+		}
+	}
+
+	return input, len(input)
+}
+
+// Expand a single quoted string starting after a '\''
+func expandSingleQuoted(input string) (string, int) {
+	j := strings.Index(input, "'")
+	if j < 0 {
+		return input, len(input)
+	}
+	return input[:j], (j + 1)
+}
+
+// Expand something starting with at '$'.
+func expandSigil(input string, vars map[string][]string) ([]string, int) {
+	c, w := utf8.DecodeRuneInString(input)
+	var offset int
+	var varname string
+
+	// escaping of "$" with "$$"
+	if c == '$' {
+		return []string{"$"}, 2
+		// match bracketed expansions: ${foo}, or ${foo:a%b=c%d}
+	} else if c == '{' {
+		var namelist_pattern = regexp.MustCompile(
+			`^\s*([^:]+)\s*:\s*([^%]*)%([^=]*)\s*=\s*([^%]*)%([^%]*)\s*`)
+		j := strings.IndexRune(input[w:], '}')
+		if j < 0 {
+			return []string{"$" + input}, len(input)
+		}
+		varname = input[w : w+j]
+		offset = w + j + 1
+
+		// is this a namelist?
+		mat := namelist_pattern.FindStringSubmatch(varname)
+		if mat != nil && isValidVarName(mat[1]) {
+			// ${varname:a%b=c%d}
+			varname = mat[1]
+			a, b, c, d := mat[2], mat[3], mat[4], mat[5]
+			values, ok := vars[varname]
+			if !ok {
+				return []string{}, offset
+			}
+
+			pat := regexp.MustCompile(strings.Join([]string{`^\Q`, a, `\E(.*)\Q`, b, `\E$`}, ""))
+			expanded_values := make([]string, len(values))
+			for i, value := range values {
+				value_match := pat.FindStringSubmatch(value)
+				if value_match != nil {
+					expanded_values[i] = strings.Join([]string{c, value_match[1], d}, "")
+				} else {
+					expanded_values[i] = value
+				}
+			}
+
+			return expanded_values, offset
+		}
+		// bare variables: $foo
+	} else if c == '(' { // Environment variables.
+		j := strings.IndexRune(input[w:], ')')
+		if j < 0 {
+			return []string{"$" + input}, len(input)
+		}
+		varname = input[w : w+j]
+		offset = w + j + 1
+
+		return []string{os.Getenv(varname)}, offset
+	} else {
+		// try to match a variable name
+		i := 0
+		j := i
+		for j < len(input) {
+			c, w = utf8.DecodeRuneInString(input[j:])
+			if !(isalpha(c) || c == '_' || (j > i && isdigit(c))) {
+				break
+			}
+			j += w
+		}
+
+		if j > i {
+			varname = input[i:j]
+			offset = j
+		} else {
+			return []string{"$" + input}, len(input)
+		}
+	}
+
+	if isValidVarName(varname) {
+		varvals, ok := vars[varname]
+		if ok {
+			return varvals, offset
+		} else {
+			return []string{"$" + input[:offset]}, offset
+		}
+	}
+
+	return []string{"$" + input}, len(input)
+}
+
+// Find and expand all sigils.
+func expandSigils(input string, vars map[string][]string) []string {
+	parts := make([]string, 0)
+	expanded := ""
+	for i := 0; i < len(input); {
+		j := strings.IndexRune(input[i:], '$')
+		if j < 0 {
+			expanded += input[i:]
+			break
+		}
+
+		ex, k := expandSigil(input[j+1:], vars)
+		if len(ex) > 0 {
+			ex[0] = expanded + ex[0]
+			expanded = ex[len(ex)-1]
+			parts = append(parts, ex[:len(ex)-1]...)
+		}
+		i = k
+	}
+
+	if len(expanded) > 0 {
+		parts = append(parts, expanded)
+	}
+
+	return parts
+}
+
+// Find and expand all sigils in a recipe, producing a flat string.
+func expandRecipeSigils(input string, vars map[string][]string) string {
+	expanded := ""
+	for i := 0; i < len(input); {
+		off := strings.IndexAny(input[i:], "$\\")
+		if off < 0 {
+			expanded += input[i:]
+			break
+		}
+		expanded += input[i : i+off]
+		i += off
+
+		c, w := utf8.DecodeRuneInString(input[i:])
+		if c == '$' {
+			i += w
+			ex, k := expandSigil(input[i:], vars)
+			expanded += strings.Join(ex, " ")
+			i += k
+		} else if c == '\\' {
+			i += w
+			c, w := utf8.DecodeRuneInString(input[i:])
+			if c == '$' {
+				expanded += "$"
+			} else {
+				expanded += "\\" + string(c)
+			}
+			i += w
+		}
+	}
+
+	return expanded
+}
+
+// Expand all unescaped '%' characters.
+func expandSuffixes(input string, stem string) string {
+	expanded := make([]byte, 0)
+	for i := 0; i < len(input); {
+		j := strings.IndexAny(input[i:], "\\%")
+		if j < 0 {
+			expanded = append(expanded, input[i:]...)
+			break
+		}
+
+		c, w := utf8.DecodeRuneInString(input[j:])
+		expanded = append(expanded, input[i:j]...)
+		if c == '%' {
+			expanded = append(expanded, stem...)
+			i = j + w
+		} else {
+			j += w
+			c, w := utf8.DecodeRuneInString(input[j:])
+			if c == '%' {
+				expanded = append(expanded, '%')
+				i = j + w
+			}
+		}
+	}
+
+	return string(expanded)
+}
+
+// Expand a backtick quoted string, by executing the contents.
+func expandBackQuoted(input string, vars map[string][]string) ([]string, int) {
+	// TODO: expand sigils?
+	j := strings.Index(input, "`")
+	if j < 0 {
+		return []string{input}, len(input)
+	}
+
+	// TODO: handle errors
+	output, _ := subprocess("sh", nil, input[:j], true)
+
+	parts := make([]string, 0)
+	_, tokens := lexWords(output)
+	for t := range tokens {
+		parts = append(parts, t.val)
+	}
+
+	return parts, (j + 1)
+}
diff --git a/src/tool/mk/graph.go b/src/tool/mk/graph.go
new file mode 100644
index 0000000..a5bc60b
--- /dev/null
+++ b/src/tool/mk/graph.go
@@ -0,0 +1,371 @@
+package mk
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"sync"
+	"time"
+)
+
+// A dependency graph
+type graph struct {
+	root  *node            // the intial target's node
+	nodes map[string]*node // map targets to their nodes
+}
+
+// An edge in the graph.
+type edge struct {
+	v       *node    // node this edge directs to
+	stem    string   // stem matched for meta-rule applications
+	matches []string // regular expression matches
+	togo    bool     // this edge is going to be pruned
+	r       *rule
+}
+
+// Current status of a node in the build.
+type nodeStatus int
+
+const (
+	nodeStatusReady nodeStatus = iota
+	nodeStatusStarted
+	nodeStatusNop
+	nodeStatusDone
+	nodeStatusFailed
+)
+
+type nodeFlag int
+
+const (
+	nodeFlagCycle    nodeFlag = 0x0002
+	nodeFlagReady             = 0x0004
+	nodeFlagProbable          = 0x0100
+	nodeFlagVacuous           = 0x0200
+)
+
+// A node in the dependency graph
+type node struct {
+	r         *rule             // rule to be applied
+	name      string            // target name
+	prog      string            // custom program to compare times
+	t         time.Time         // file modification time
+	exists    bool              // does a non-virtual target exist
+	prereqs   []*edge           // prerequisite rules
+	status    nodeStatus        // current state of the node in the build
+	mutex     sync.Mutex        // exclusivity for the status variable
+	listeners []chan nodeStatus // channels to notify of completion
+	flags     nodeFlag          // bitwise combination of node flags
+}
+
+// Update a node's timestamp and 'exists' flag.
+func (u *node) updateTimestamp() {
+	info, err := os.Stat(u.name)
+	if err == nil {
+		u.t = info.ModTime()
+		u.exists = true
+		u.flags |= nodeFlagProbable
+	} else {
+		_, ok := err.(*os.PathError)
+		if ok {
+			u.t = time.Unix(0, 0)
+			u.exists = false
+		} else {
+			mkError(err.Error())
+		}
+	}
+
+	if rebuildall {
+		u.flags |= nodeFlagProbable
+	}
+}
+
+// Create a new node
+func (g *graph) newnode(name string) *node {
+	u := &node{name: name}
+	u.updateTimestamp()
+	g.nodes[name] = u
+	return u
+}
+
+// Print a graph in graphviz format.
+func (g *graph) visualize(w io.Writer) {
+	fmt.Fprintln(w, "digraph mk {")
+	for t, u := range g.nodes {
+		for i := range u.prereqs {
+			if u.prereqs[i].v != nil {
+				fmt.Fprintf(w, "    \"%s\" -> \"%s\";\n", t, u.prereqs[i].v.name)
+			}
+		}
+	}
+	fmt.Fprintln(w, "}")
+}
+
+// Create a new arc.
+func (u *node) newedge(v *node, r *rule) *edge {
+	e := &edge{v: v, r: r}
+	u.prereqs = append(u.prereqs, e)
+	return e
+}
+
+// Create a dependency graph for the given target.
+func buildgraph(rs *ruleSet, target string) *graph {
+	g := &graph{nil, make(map[string]*node)}
+
+	// keep track of how many times each rule is visited, to avoid cycles.
+	rulecnt := make([]int, len(rs.rules))
+	g.root = applyrules(rs, g, target, rulecnt)
+	g.cyclecheck(g.root)
+	g.root.flags |= nodeFlagProbable
+	g.vacuous(g.root)
+	g.ambiguous(g.root)
+
+	return g
+}
+
+// Recursively match the given target to a rule in the rule set to construct the
+// full graph.
+func applyrules(rs *ruleSet, g *graph, target string, rulecnt []int) *node {
+	u, ok := g.nodes[target]
+	if ok {
+		return u
+	}
+	u = g.newnode(target)
+
+	// does the target match a concrete rule?
+
+	ks, ok := rs.targetrules[target]
+	if ok {
+		for ki := range ks {
+			k := ks[ki]
+			if rulecnt[k] > maxRuleCnt {
+				continue
+			}
+
+			r := &rs.rules[k]
+
+			// skip meta-rules
+			if r.ismeta {
+				continue
+			}
+
+			// skip rules that have no effect
+			if r.recipe == "" && len(r.prereqs) == 0 {
+				continue
+			}
+
+			u.flags |= nodeFlagProbable
+			rulecnt[k] += 1
+			if len(r.prereqs) == 0 {
+				u.newedge(nil, r)
+			} else {
+				for i := range r.prereqs {
+					u.newedge(applyrules(rs, g, r.prereqs[i], rulecnt), r)
+				}
+			}
+			rulecnt[k] -= 1
+		}
+	}
+
+	// find applicable metarules
+	for k := range rs.rules {
+		if rulecnt[k] >= maxRuleCnt {
+			continue
+		}
+
+		r := &rs.rules[k]
+
+		if !r.ismeta {
+			continue
+		}
+
+		// skip rules that have no effect
+		if r.recipe == "" && len(r.prereqs) == 0 {
+			continue
+		}
+
+		for j := range r.targets {
+			mat := r.targets[j].match(target)
+			if mat == nil {
+				continue
+			}
+
+			var stem string
+			var matches []string
+			var match_vars = make(map[string][]string)
+
+			if r.attributes.regex {
+				matches = mat
+				for i := range matches {
+					key := fmt.Sprintf("stem%d", i)
+					match_vars[key] = matches[i : i+1]
+				}
+			} else {
+				stem = mat[1]
+			}
+
+			rulecnt[k] += 1
+			if len(r.prereqs) == 0 {
+				e := u.newedge(nil, r)
+				e.stem = stem
+				e.matches = matches
+			} else {
+				for i := range r.prereqs {
+					var prereq string
+					if r.attributes.regex {
+						prereq = expandRecipeSigils(r.prereqs[i], match_vars)
+					} else {
+						prereq = expandSuffixes(r.prereqs[i], stem)
+					}
+
+					e := u.newedge(applyrules(rs, g, prereq, rulecnt), r)
+					e.stem = stem
+					e.matches = matches
+				}
+			}
+			rulecnt[k] -= 1
+		}
+	}
+
+	return u
+}
+
+// Remove edges marked as togo.
+func (g *graph) togo(u *node) {
+	n := 0
+	for i := range u.prereqs {
+		if !u.prereqs[i].togo {
+			n++
+		}
+	}
+	prereqs := make([]*edge, n)
+	j := 0
+	for i := range u.prereqs {
+		if !u.prereqs[i].togo {
+			prereqs[j] = u.prereqs[i]
+			j++
+		}
+	}
+
+	// TODO: We may have to delete nodes from g.nodes, right?
+
+	u.prereqs = prereqs
+}
+
+// Remove vacous children of n.
+func (g *graph) vacuous(u *node) bool {
+	vac := u.flags&nodeFlagProbable == 0
+	if u.flags&nodeFlagReady != 0 {
+		return vac
+	}
+	u.flags |= nodeFlagReady
+
+	for i := range u.prereqs {
+		e := u.prereqs[i]
+		if e.v != nil && g.vacuous(e.v) && e.r.ismeta {
+			e.togo = true
+		} else {
+			vac = false
+		}
+	}
+
+	// if a rule generated edges that are not togo, keep all of its edges
+	for i := range u.prereqs {
+		e := u.prereqs[i]
+		if !e.togo {
+			for j := range u.prereqs {
+				f := u.prereqs[j]
+				if e.r == f.r {
+					f.togo = false
+				}
+			}
+		}
+	}
+
+	g.togo(u)
+	if vac {
+		u.flags |= nodeFlagVacuous
+	}
+
+	return vac
+}
+
+// Check for cycles
+func (g *graph) cyclecheck(u *node) {
+	if u.flags&nodeFlagCycle != 0 && len(u.prereqs) > 0 {
+		mkError(fmt.Sprintf("cycle in the graph detected at target %s", u.name))
+	}
+	u.flags |= nodeFlagCycle
+	for i := range u.prereqs {
+		if u.prereqs[i].v != nil {
+			g.cyclecheck(u.prereqs[i].v)
+		}
+	}
+	u.flags &= ^nodeFlagCycle
+
+}
+
+// Deal with ambiguous rules.
+func (g *graph) ambiguous(u *node) {
+	bad := 0
+	var le *edge
+	for i := range u.prereqs {
+		e := u.prereqs[i]
+
+		if e.v != nil {
+			g.ambiguous(e.v)
+		}
+		if e.r.recipe == "" {
+			continue
+		}
+		if le == nil || le.r == nil {
+			le = e
+		} else {
+			if !le.r.equivRecipe(e.r) {
+				if le.r.ismeta && !e.r.ismeta {
+					mkPrintRecipe(u.name, le.r.recipe, false)
+					le.togo = true
+					le = e
+				} else if !le.r.ismeta && e.r.ismeta {
+					mkPrintRecipe(u.name, e.r.recipe, false)
+					e.togo = true
+					continue
+				}
+			}
+			if !le.r.equivRecipe(e.r) {
+				if bad == 0 {
+					mkPrintError(fmt.Sprintf("mk: ambiguous recipes for %s\n", u.name))
+					bad = 1
+					g.trace(u.name, le)
+				}
+				g.trace(u.name, e)
+			}
+		}
+	}
+	if bad > 0 {
+		mkError("")
+	}
+	g.togo(u)
+}
+
+// Print a trace of rules, k
+func (g *graph) trace(name string, e *edge) {
+	fmt.Fprintf(os.Stderr, "\t%s", name)
+	for true {
+		prereqname := ""
+		if e.v != nil {
+			prereqname = e.v.name
+		}
+		fmt.Fprintf(os.Stderr, " <-(%s:%d)- %s", e.r.file, e.r.line, prereqname)
+		if e.v != nil {
+			for i := range e.v.prereqs {
+				if e.v.prereqs[i].r.recipe != "" {
+					e = e.v.prereqs[i]
+					continue
+				}
+			}
+			break
+		} else {
+			break
+		}
+	}
+}
diff --git a/src/tool/mk/lex.go b/src/tool/mk/lex.go
new file mode 100644
index 0000000..c0f0b23
--- /dev/null
+++ b/src/tool/mk/lex.go
@@ -0,0 +1,409 @@
+package mk
+
+import (
+	"fmt"
+	"strings"
+	"unicode/utf8"
+)
+
+type tokenType int
+
+const eof rune = '\000'
+
+// Rune's that cannot be part of a bare (unquoted) string.
+const nonBareRunes = " \t\n\r\\=:#'\"$"
+
+// Return true if the string contains whitespace only.
+func onlyWhitespace(s string) bool {
+	return strings.IndexAny(s, " \t\r\n") < 0
+}
+
+const (
+	tokenError tokenType = iota
+	tokenNewline
+	tokenWord
+	tokenPipeInclude
+	tokenRedirInclude
+	tokenColon
+	tokenAssign
+	tokenRecipe
+)
+
+func (typ tokenType) String() string {
+	switch typ {
+	case tokenError:
+		return "[Error]"
+	case tokenNewline:
+		return "[Newline]"
+	case tokenWord:
+		return "[Word]"
+	case tokenPipeInclude:
+		return "[PipeInclude]"
+	case tokenRedirInclude:
+		return "[RedirInclude]"
+	case tokenColon:
+		return "[Colon]"
+	case tokenAssign:
+		return "[Assign]"
+	case tokenRecipe:
+		return "[Recipe]"
+	}
+	return "[MysteryToken]"
+}
+
+type token struct {
+	typ  tokenType // token type
+	val  string    // token string
+	line int       // line where it was found
+	col  int       // column on which the token began
+}
+
+func (t *token) String() string {
+	if t.typ == tokenError {
+		return t.val
+	} else if t.typ == tokenNewline {
+		return "\\n"
+	}
+
+	return t.val
+}
+
+type lexer struct {
+	input     string     // input string to be lexed
+	output    chan token // channel on which tokens are sent
+	start     int        // token beginning
+	startcol  int        // column on which the token begins
+	pos       int        // position within input
+	line      int        // line within input
+	col       int        // column within input
+	errmsg    string     // set to an appropriate error message when necessary
+	indented  bool       // true if the only whitespace so far on this line
+	barewords bool       // lex only a sequence of words
+}
+
+// A lexerStateFun is simultaneously the the state of the lexer and the next
+// action the lexer will perform.
+type lexerStateFun func(*lexer) lexerStateFun
+
+func (l *lexer) lexerror(what string) {
+	if l.errmsg == "" {
+		l.errmsg = what
+	}
+	l.emit(tokenError)
+}
+
+// Return the nth character without advancing.
+func (l *lexer) peekN(n int) (c rune) {
+	pos := l.pos
+	var width int
+	i := 0
+	for ; i <= n && pos < len(l.input); i++ {
+		c, width = utf8.DecodeRuneInString(l.input[pos:])
+		pos += width
+	}
+
+	if i <= n {
+		return eof
+	}
+
+	return
+}
+
+// Return the next character without advancing.
+func (l *lexer) peek() rune {
+	return l.peekN(0)
+}
+
+// Consume and return the next character in the lexer input.
+func (l *lexer) next() rune {
+	if l.pos >= len(l.input) {
+		return eof
+	}
+	c, width := utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += width
+
+	if c == '\n' {
+		l.col = 0
+		l.line += 1
+		l.indented = true
+	} else {
+		l.col += 1
+		if strings.IndexRune(" \t", c) < 0 {
+			l.indented = false
+		}
+	}
+
+	return c
+}
+
+// Skip and return the next character in the lexer input.
+func (l *lexer) skip() {
+	l.next()
+	l.start = l.pos
+	l.startcol = l.col
+}
+
+func (l *lexer) emit(typ tokenType) {
+	l.output <- token{typ, l.input[l.start:l.pos], l.line, l.startcol}
+	l.start = l.pos
+	l.startcol = 0
+}
+
+// Consume the next run if it is in the given string.
+func (l *lexer) accept(valid string) bool {
+	if strings.IndexRune(valid, l.peek()) >= 0 {
+		l.next()
+		return true
+	}
+	return false
+}
+
+// Skip the next rune if it is in the valid string. Return true if it was
+// skipped.
+func (l *lexer) ignore(valid string) bool {
+	if strings.IndexRune(valid, l.peek()) >= 0 {
+		l.skip()
+		return true
+	}
+	return false
+}
+
+// Consume characters from the valid string until the next is not.
+func (l *lexer) acceptRun(valid string) int {
+	prevpos := l.pos
+	for strings.IndexRune(valid, l.peek()) >= 0 {
+		l.next()
+	}
+	return l.pos - prevpos
+}
+
+// Accept until something from the given string is encountered.
+func (l *lexer) acceptUntil(invalid string) {
+	for l.pos < len(l.input) && strings.IndexRune(invalid, l.peek()) < 0 {
+		l.next()
+	}
+
+	if l.peek() == eof {
+		l.lexerror(fmt.Sprintf("end of file encountered while looking for one of: %s", invalid))
+	}
+}
+
+// Accept until something from the given string is encountered, or the end of th
+// file
+func (l *lexer) acceptUntilOrEof(invalid string) {
+	for l.pos < len(l.input) && strings.IndexRune(invalid, l.peek()) < 0 {
+		l.next()
+	}
+}
+
+// Skip characters from the valid string until the next is not.
+func (l *lexer) skipRun(valid string) int {
+	prevpos := l.pos
+	for strings.IndexRune(valid, l.peek()) >= 0 {
+		l.skip()
+	}
+	return l.pos - prevpos
+}
+
+// Skip until something from the given string is encountered.
+func (l *lexer) skipUntil(invalid string) {
+	for l.pos < len(l.input) && strings.IndexRune(invalid, l.peek()) < 0 {
+		l.skip()
+	}
+
+	if l.peek() == eof {
+		l.lexerror(fmt.Sprintf("end of file encountered while looking for one of: %s", invalid))
+	}
+}
+
+// Start a new lexer to lex the given input.
+func lex(input string) (*lexer, chan token) {
+	l := &lexer{input: input, output: make(chan token), line: 1, col: 0, indented: true}
+	go l.run()
+	return l, l.output
+}
+
+func lexWords(input string) (*lexer, chan token) {
+	l := &lexer{input: input, output: make(chan token), line: 1, col: 0, indented: true, barewords: true}
+	go l.run()
+	return l, l.output
+}
+
+func (l *lexer) run() {
+	for state := lexTopLevel; state != nil; {
+		state = state(l)
+	}
+	close(l.output)
+}
+
+func lexTopLevel(l *lexer) lexerStateFun {
+	for {
+		l.skipRun(" \t\r")
+		// emit a newline token if we are ending a non-empty line.
+		if l.peek() == '\n' && !l.indented {
+			l.next()
+			if l.barewords {
+				return nil
+			} else {
+				l.emit(tokenNewline)
+			}
+		}
+		l.skipRun(" \t\r\n")
+
+		if l.peek() == '\\' && l.peekN(1) == '\n' {
+			l.next()
+			l.next()
+			l.indented = false
+		} else {
+			break
+		}
+	}
+
+	if l.indented && l.col > 0 {
+		return lexRecipe
+	}
+
+	c := l.peek()
+	switch c {
+	case eof:
+		return nil
+	case '#':
+		return lexComment
+	case '<':
+		return lexInclude
+	case ':':
+		return lexColon
+	case '=':
+		return lexAssign
+	case '"':
+		return lexDoubleQuotedWord
+	case '\'':
+		return lexSingleQuotedWord
+	case '`':
+		return lexBackQuotedWord
+	}
+
+	return lexBareWord
+}
+
+func lexColon(l *lexer) lexerStateFun {
+	l.next()
+	l.emit(tokenColon)
+	return lexTopLevel
+}
+
+func lexAssign(l *lexer) lexerStateFun {
+	l.next()
+	l.emit(tokenAssign)
+	return lexTopLevel
+}
+
+func lexComment(l *lexer) lexerStateFun {
+	l.skip() // '#'
+	l.skipUntil("\n")
+	return lexTopLevel
+}
+
+func lexInclude(l *lexer) lexerStateFun {
+	l.next() // '<'
+	if l.accept("|") {
+		l.emit(tokenPipeInclude)
+	} else {
+		l.emit(tokenRedirInclude)
+	}
+	return lexTopLevel
+}
+
+func lexDoubleQuotedWord(l *lexer) lexerStateFun {
+	l.next() // '"'
+	for l.peek() != '"' && l.peek() != eof {
+		l.acceptUntil("\\\"")
+		if l.accept("\\") {
+			l.accept("\"")
+		}
+	}
+
+	if l.peek() == eof {
+		l.lexerror("end of file encountered while parsing a quoted string.")
+	}
+
+	l.next() // '"'
+	return lexBareWord
+}
+
+func lexBackQuotedWord(l *lexer) lexerStateFun {
+	l.next() // '`'
+	l.acceptUntil("`")
+	l.next() // '`'
+	return lexBareWord
+}
+
+func lexSingleQuotedWord(l *lexer) lexerStateFun {
+	l.next() // '\''
+	l.acceptUntil("'")
+	l.next() // '\''
+	return lexBareWord
+}
+
+func lexRecipe(l *lexer) lexerStateFun {
+	for {
+		l.acceptUntilOrEof("\n")
+		l.acceptRun(" \t\n\r")
+		if !l.indented || l.col == 0 {
+			break
+		}
+	}
+
+	if !onlyWhitespace(l.input[l.start:l.pos]) {
+		l.emit(tokenRecipe)
+	}
+	return lexTopLevel
+}
+
+func lexBareWord(l *lexer) lexerStateFun {
+	l.acceptUntil(nonBareRunes)
+	c := l.peek()
+	if c == '"' {
+		return lexDoubleQuotedWord
+	} else if c == '\'' {
+		return lexSingleQuotedWord
+	} else if c == '`' {
+		return lexBackQuotedWord
+	} else if c == '\\' {
+		c1 := l.peekN(1)
+		if c1 == '\n' || c1 == '\r' {
+			if l.start < l.pos {
+				l.emit(tokenWord)
+			}
+			l.skip()
+			l.skip()
+			return lexTopLevel
+		} else {
+			l.next()
+			l.next()
+			return lexBareWord
+		}
+	} else if c == '$' {
+		c1 := l.peekN(1)
+		if c1 == '{' {
+			return lexBracketExpansion
+		} else {
+			l.next()
+			return lexBareWord
+		}
+	}
+
+	if l.start < l.pos {
+		l.emit(tokenWord)
+	}
+
+	return lexTopLevel
+}
+
+func lexBracketExpansion(l *lexer) lexerStateFun {
+	l.next() // '$'
+	l.next() // '{'
+	l.acceptUntil("}")
+	l.next() // '}'
+	return lexBareWord
+}
diff --git a/src/tool/mk/main.go b/src/tool/mk/main.go
new file mode 100644
index 0000000..91d6254
--- /dev/null
+++ b/src/tool/mk/main.go
@@ -0,0 +1,417 @@
+package mk
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+)
+
+// True if messages should be printed without fancy colors.
+var nocolor bool = false
+
+// True if we are ignoring timestamps and rebuilding everything.
+var rebuildall bool = false
+
+// Set of targets for which we are forcing rebuild
+var rebuildtargets map[string]bool = make(map[string]bool)
+
+// Lock on standard out, messages don't get interleaved too much.
+var mkMsgMutex sync.Mutex
+
+// The maximum number of times an rule may be applied.
+const maxRuleCnt = 1
+
+// Limit the number of recipes executed simultaneously.
+var subprocsAllowed int
+
+// Current subprocesses being executed
+var subprocsRunning int
+
+// Wakeup on a free subprocess slot.
+var subprocsRunningCond *sync.Cond = sync.NewCond(&sync.Mutex{})
+
+// Prevent more than one recipe at a time from trying to take over
+var exclusiveSubproc = sync.Mutex{}
+
+// Wait until there is an available subprocess slot.
+func reserveSubproc() {
+	subprocsRunningCond.L.Lock()
+	for subprocsRunning >= subprocsAllowed {
+		subprocsRunningCond.Wait()
+	}
+	subprocsRunning++
+	subprocsRunningCond.L.Unlock()
+}
+
+// Free up another subprocess to run.
+func finishSubproc() {
+	subprocsRunningCond.L.Lock()
+	subprocsRunning--
+	subprocsRunningCond.Signal()
+	subprocsRunningCond.L.Unlock()
+}
+
+// Make everyone wait while we
+func reserveExclusiveSubproc() {
+	exclusiveSubproc.Lock()
+	// Wait until everything is done running
+	stolen_subprocs := 0
+	subprocsRunningCond.L.Lock()
+	stolen_subprocs = subprocsAllowed - subprocsRunning
+	subprocsRunning = subprocsAllowed
+	for stolen_subprocs < subprocsAllowed {
+		subprocsRunningCond.Wait()
+		stolen_subprocs += subprocsAllowed - subprocsRunning
+		subprocsRunning = subprocsAllowed
+	}
+}
+
+func finishExclusiveSubproc() {
+	subprocsRunning = 0
+	subprocsRunningCond.Broadcast()
+	subprocsRunningCond.L.Unlock()
+	exclusiveSubproc.Unlock()
+}
+
+// Ansi color codes.
+const (
+	ansiTermDefault   = "\033[0m"
+	ansiTermBlack     = "\033[30m"
+	ansiTermRed       = "\033[31m"
+	ansiTermGreen     = "\033[32m"
+	ansiTermYellow    = "\033[33m"
+	ansiTermBlue      = "\033[34m"
+	ansiTermMagenta   = "\033[35m"
+	ansiTermBright    = "\033[1m"
+	ansiTermUnderline = "\033[4m"
+)
+
+// Build a node's prereqs. Block until completed.
+//
+func mkNodePrereqs(g *graph, u *node, e *edge, prereqs []*node, dryrun bool,
+	required bool) nodeStatus {
+	prereqstat := make(chan nodeStatus)
+	pending := 0
+
+	// build prereqs that need building
+	for i := range prereqs {
+		prereqs[i].mutex.Lock()
+		switch prereqs[i].status {
+		case nodeStatusReady, nodeStatusNop:
+			go mkNode(g, prereqs[i], dryrun, required)
+			fallthrough
+		case nodeStatusStarted:
+			prereqs[i].listeners = append(prereqs[i].listeners, prereqstat)
+			pending++
+		}
+		prereqs[i].mutex.Unlock()
+	}
+
+	// wait until all the prereqs are built
+	status := nodeStatusDone
+	for pending > 0 {
+		s := <-prereqstat
+		pending--
+		if s == nodeStatusFailed {
+			status = nodeStatusFailed
+		}
+	}
+	return status
+}
+
+// Build a target in the graph.
+//
+// This selects an appropriate rule (edge) and builds all prerequisites
+// concurrently.
+//
+// Args:
+//  g: Graph in which the node lives.
+//  u: Node to (possibly) build.
+//  dryrun: Don't actually build anything, just pretend.
+//  required: Avoid building this node, unless its prereqs are out of date.
+//
+func mkNode(g *graph, u *node, dryrun bool, required bool) {
+	// try to claim on this node
+	u.mutex.Lock()
+	if u.status != nodeStatusReady && u.status != nodeStatusNop {
+		u.mutex.Unlock()
+		return
+	} else {
+		u.status = nodeStatusStarted
+	}
+	u.mutex.Unlock()
+
+	// when finished, notify the listeners
+	finalstatus := nodeStatusDone
+	defer func() {
+		u.mutex.Lock()
+		u.status = finalstatus
+		for i := range u.listeners {
+			u.listeners[i] <- u.status
+		}
+		u.listeners = u.listeners[0:0]
+		u.mutex.Unlock()
+	}()
+
+	// there's no fucking rules, dude
+	if len(u.prereqs) == 0 {
+		if !(u.r != nil && u.r.attributes.virtual) && !u.exists {
+			wd, _ := os.Getwd()
+			mkError(fmt.Sprintf("don't know how to make %s in %s\n", u.name, wd))
+		}
+		finalstatus = nodeStatusNop
+		return
+	}
+
+	// there should otherwise be exactly one edge with an associated rule
+	prereqs := make([]*node, 0)
+	var e *edge = nil
+	for i := range u.prereqs {
+		if u.prereqs[i].r != nil {
+			e = u.prereqs[i]
+		}
+		if u.prereqs[i].v != nil {
+			prereqs = append(prereqs, u.prereqs[i].v)
+		}
+	}
+
+	// this should have been caught during graph building
+	if e == nil {
+		wd, _ := os.Getwd()
+		mkError(fmt.Sprintf("don't know how to make %s in %s", u.name, wd))
+	}
+
+	prereqs_required := required && (e.r.attributes.virtual || !u.exists)
+	mkNodePrereqs(g, u, e, prereqs, dryrun, prereqs_required)
+
+	uptodate := true
+	if !e.r.attributes.virtual {
+		u.updateTimestamp()
+		if !u.exists && required {
+			uptodate = false
+		} else if u.exists || required {
+			for i := range prereqs {
+				if u.t.Before(prereqs[i].t) || prereqs[i].status == nodeStatusDone {
+					uptodate = false
+				}
+			}
+		} else if required {
+			uptodate = false
+		}
+	} else {
+		uptodate = false
+	}
+
+	_, isrebuildtarget := rebuildtargets[u.name]
+	if isrebuildtarget || rebuildall {
+		uptodate = false
+	}
+
+	// make another pass on the prereqs, since we know we need them now
+	if !uptodate {
+		mkNodePrereqs(g, u, e, prereqs, dryrun, true)
+	}
+
+	// execute the recipe, unless the prereqs failed
+	if !uptodate && finalstatus != nodeStatusFailed && len(e.r.recipe) > 0 {
+		if e.r.attributes.exclusive {
+			reserveExclusiveSubproc()
+		} else {
+			reserveSubproc()
+		}
+
+		if !dorecipe(u.name, u, e, dryrun) {
+			finalstatus = nodeStatusFailed
+		}
+		u.updateTimestamp()
+
+		if e.r.attributes.exclusive {
+			finishExclusiveSubproc()
+		} else {
+			finishSubproc()
+		}
+	} else if finalstatus != nodeStatusFailed {
+		finalstatus = nodeStatusNop
+	}
+}
+
+func mkWarn(msg string) {
+	mkPrintWarn(msg)
+}
+
+func mkPrintWarn(msg string) {
+	if !nocolor {
+		os.Stderr.WriteString(ansiTermYellow)
+	}
+
+	fmt.Fprintf(os.Stderr, "%s\n", msg)
+
+	if !nocolor {
+		os.Stderr.WriteString(ansiTermDefault)
+	}
+}
+
+func mkError(msg string) {
+	mkPrintError(msg)
+	os.Exit(1)
+}
+
+func mkPrintError(msg string) {
+	if !nocolor {
+		os.Stderr.WriteString(ansiTermRed)
+	}
+	fmt.Fprintf(os.Stderr, "%s\n", msg)
+	if !nocolor {
+		os.Stderr.WriteString(ansiTermDefault)
+	}
+}
+
+func mkPrintSuccess(msg string) {
+	if nocolor {
+		fmt.Println(msg)
+	} else {
+		fmt.Printf("%s%s%s\n", ansiTermGreen, msg, ansiTermDefault)
+	}
+}
+
+func mkPrintMessage(msg string) {
+	mkMsgMutex.Lock()
+	if nocolor {
+		fmt.Println(msg)
+	} else {
+		fmt.Printf("%s%s%s\n", ansiTermBlue, msg, ansiTermDefault)
+	}
+	mkMsgMutex.Unlock()
+}
+
+func mkPrintRecipe(target string, recipe string, quiet bool) {
+	mkMsgMutex.Lock()
+	if nocolor {
+		fmt.Printf("%s: ", target)
+	} else {
+		fmt.Printf("%s%s%s → %s",
+			ansiTermBlue+ansiTermBright+ansiTermUnderline, target,
+			ansiTermDefault, ansiTermBlue)
+	}
+	if quiet {
+		if nocolor {
+			fmt.Println("...")
+		} else {
+			fmt.Println("…")
+		}
+	} else {
+		printIndented(os.Stdout, recipe, len(target)+3)
+		if len(recipe) == 0 {
+			os.Stdout.WriteString("\n")
+		}
+	}
+	if !nocolor {
+		os.Stdout.WriteString(ansiTermDefault)
+	}
+	mkMsgMutex.Unlock()
+}
+
+func Run(args []string) {
+	var mkfilepath string
+	var interactive bool
+	var dryrun bool
+	var shallowrebuild bool
+	var quiet bool
+
+	arg0 := args[0]
+	args = args[1:]
+
+	if mkincdir := os.Getenv("MKINCDIR") ; mkincdir == "" {
+		homeDir, _ := os.UserHomeDir()
+		os.Setenv("MKINCDIR", homeDir + "/app/mk/inc" )
+	}
+
+	flags := flag.NewFlagSet(arg0, flag.ExitOnError)
+
+	flags.StringVar(&mkfilepath, "f", "mkfile", "use the given file as mkfile")
+	flags.BoolVar(&dryrun, "n", false, "print commands without actually executing")
+	flags.BoolVar(&shallowrebuild, "r", false, "force building of just targets")
+	flags.BoolVar(&rebuildall, "a", false, "force building of all dependencies")
+	flags.IntVar(&subprocsAllowed, "p", 4, "maximum number of jobs to execute in parallel")
+	flags.BoolVar(&interactive, "i", false, "prompt before executing rules")
+	flags.BoolVar(&quiet, "q", false, "don't print recipes before executing them")
+	flags.Parse(args)
+
+	mkfile, err := os.Open(mkfilepath)
+	if err != nil {
+		mkError("no mkfile found")
+	}
+	input, _ := ioutil.ReadAll(mkfile)
+	mkfile.Close()
+
+	abspath, err := filepath.Abs(mkfilepath)
+	if err != nil {
+		mkError("unable to find mkfile's absolute path")
+	}
+
+	rs := parse(string(input), mkfilepath, abspath)
+	if quiet {
+		for i := range rs.rules {
+			rs.rules[i].attributes.quiet = true
+		}
+	}
+
+	targets := flags.Args()
+
+	// build the first non-meta rule in the makefile, if none are given explicitly
+	if len(targets) == 0 {
+		for i := range rs.rules {
+			if !rs.rules[i].ismeta {
+				for j := range rs.rules[i].targets {
+					targets = append(targets, rs.rules[i].targets[j].spat)
+				}
+				break
+			}
+		}
+	}
+
+	if len(targets) == 0 {
+		fmt.Println("mk: nothing to mk")
+		return
+	}
+
+	if shallowrebuild {
+		for i := range targets {
+			rebuildtargets[targets[i]] = true
+		}
+	}
+
+	// Create a dummy virtual rule that depends on every target
+	root := rule{}
+	root.targets = []pattern{pattern{false, "", nil}}
+	root.attributes = attribSet{false, false, false, false, false, false, false, true, false}
+	root.prereqs = targets
+	rs.add(root)
+
+	if interactive {
+		g := buildgraph(rs, "")
+		mkNode(g, g.root, true, true)
+		fmt.Print("Proceed? ")
+		in := bufio.NewReader(os.Stdin)
+		for {
+			c, _, err := in.ReadRune()
+			if err != nil {
+				return
+			} else if strings.IndexRune(" \n\t\r", c) >= 0 {
+				continue
+			} else if c == 'y' {
+				break
+			} else {
+				return
+			}
+		}
+	}
+
+	g := buildgraph(rs, "")
+	mkNode(g, g.root, dryrun, true)
+}
diff --git a/src/tool/mk/parse.go b/src/tool/mk/parse.go
new file mode 100644
index 0000000..ef6c2d8
--- /dev/null
+++ b/src/tool/mk/parse.go
@@ -0,0 +1,384 @@
+// This is a mkfile parser. It executes assignments and includes as it goes, and
+// collects a set of rules, which are returned as a ruleSet object.
+
+package mk
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+type parser struct {
+	l        *lexer   // underlying lexer
+	name     string   // name of the file being parsed
+	path     string   // full path of the file being parsed
+	tokenbuf []token  // tokens consumed on the current statement
+	rules    *ruleSet // current ruleSet
+}
+
+// Pretty errors.
+func (p *parser) parseError(context string, expected string, found token) {
+	mkPrintError(fmt.Sprintf("%s:%d: syntax error: ", p.name, found.line))
+	mkPrintError(fmt.Sprintf("while %s, expected %s but found '%s'.\n",
+		context, expected, found.String()))
+	mkError("")
+}
+
+func (p *parser) basicWarnAtToken(what string, found token) {
+	p.basicWarnAtLine(what, found.line)
+}
+
+func (p *parser) basicWarnAtLine(what string, line int) {
+	mkWarn(fmt.Sprintf("%s:%d: warning: %s\n", p.name, line, what))
+}
+
+// More basic errors.
+func (p *parser) basicErrorAtToken(what string, found token) {
+	p.basicErrorAtLine(what, found.line)
+}
+
+func (p *parser) basicErrorAtLine(what string, line int) {
+	mkError(fmt.Sprintf("%s:%d: syntax error: %s\n", p.name, line, what))
+}
+
+// Accept a token for use in the current statement being parsed.
+func (p *parser) push(t token) {
+	p.tokenbuf = append(p.tokenbuf, t)
+}
+
+// Clear all the accepted tokens. Called when a statement is finished.
+func (p *parser) clear() {
+	p.tokenbuf = p.tokenbuf[:0]
+}
+
+// A parser state function takes a parser and the next token and returns a new
+// state function, or nil if there was a parse error.
+type parserStateFun func(*parser, token) parserStateFun
+
+// Parse a mkfile, returning a new ruleSet.
+func parse(input string, name string, path string) *ruleSet {
+	rules := &ruleSet{make(map[string][]string),
+		make([]rule, 0),
+		make(map[string][]int)}
+	parseInto(input, name, rules, path)
+	return rules
+}
+
+// Parse a mkfile inserting rules and variables into a given ruleSet.
+func parseInto(input string, name string, rules *ruleSet, path string) {
+	l, tokens := lex(input)
+	p := &parser{l, name, path, []token{}, rules}
+	oldmkfiledir := p.rules.vars["mkfiledir"]
+	p.rules.vars["mkfiledir"] = []string{filepath.Dir(path)}
+	state := parseTopLevel
+	for t := range tokens {
+		if t.typ == tokenError {
+			p.basicErrorAtLine(l.errmsg, t.line)
+			break
+		}
+
+		state = state(p, t)
+	}
+
+	// insert a dummy newline to allow parsing of any assignments or recipeless
+	// rules to finish.
+	state = state(p, token{tokenNewline, "\n", l.line, l.col})
+
+	p.rules.vars["mkfiledir"] = oldmkfiledir
+
+	// TODO: Error when state != parseTopLevel
+}
+
+// We are at the top level of a mkfile, expecting rules, assignments, or
+// includes.
+func parseTopLevel(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		return parseTopLevel
+	case tokenPipeInclude:
+		return parsePipeInclude
+	case tokenRedirInclude:
+		return parseRedirInclude
+	case tokenWord:
+		return parseAssignmentOrTarget(p, t)
+	default:
+		p.parseError("parsing mkfile",
+			"a rule, include, or assignment", t)
+	}
+
+	return parseTopLevel
+}
+
+// Consumed a '<|'
+func parsePipeInclude(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		if len(p.tokenbuf) == 0 {
+			p.basicErrorAtToken("empty pipe include", t)
+		}
+
+		args := make([]string, len(p.tokenbuf))
+		for i := 0; i < len(p.tokenbuf); i++ {
+			args[i] = p.tokenbuf[i].val
+		}
+
+		output, success := subprocess("sh", args, "", true)
+		if !success {
+			p.basicErrorAtToken("subprocess include failed", t)
+		}
+
+		parseInto(output, fmt.Sprintf("%s:sh", p.name), p.rules, p.path)
+
+		p.clear()
+		return parseTopLevel
+
+	// Almost anything goes. Let the shell sort it out.
+	case tokenPipeInclude:
+		fallthrough
+	case tokenRedirInclude:
+		fallthrough
+	case tokenColon:
+		fallthrough
+	case tokenAssign:
+		fallthrough
+	case tokenWord:
+		p.tokenbuf = append(p.tokenbuf, t)
+
+	default:
+		p.parseError("parsing piped include", "a shell command", t)
+	}
+
+	return parsePipeInclude
+}
+
+// Consumed a '<'
+func parseRedirInclude(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		filename := ""
+		//fmt.Printf("'%v'\n", p.tokenbuf)
+		for i := range p.tokenbuf {
+			filename += expand(p.tokenbuf[i].val, p.rules.vars, true)[0]
+		}
+		file, err := os.Open(filename)
+		if err != nil {
+			p.basicWarnAtToken(fmt.Sprintf("cannot open %s", filename), p.tokenbuf[0])
+			//p.basicErrorAtToken(fmt.Sprintf("cannot open %s", filename), p.tokenbuf[0])
+		}
+		input, _ := ioutil.ReadAll(file)
+
+		path, err := filepath.Abs(filename)
+		if err != nil {
+			mkError("unable to find mkfile's absolute path")
+		}
+
+		parseInto(string(input), filename, p.rules, path)
+
+		p.clear()
+		return parseTopLevel
+
+	case tokenWord:
+		p.tokenbuf = append(p.tokenbuf, t)
+
+	default:
+		p.parseError("parsing include", "a file name", t)
+	}
+
+	return parseRedirInclude
+}
+
+// Encountered a bare string at the beginning of the line.
+func parseAssignmentOrTarget(p *parser, t token) parserStateFun {
+	p.push(t)
+	return parseEqualsOrTarget
+}
+
+// Consumed one bare string ot the beginning of the line.
+func parseEqualsOrTarget(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenAssign:
+		return parseAssignment
+
+	case tokenWord:
+		p.push(t)
+		return parseTargets
+
+	case tokenColon:
+		p.push(t)
+		return parseAttributesOrPrereqs
+
+	default:
+		p.parseError("reading a target or assignment",
+			"'=', ':', or another target", t)
+	}
+
+	return parseTopLevel // unreachable
+}
+
+// Consumed 'foo='. Everything else is a value being assigned to foo.
+func parseAssignment(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		err := p.rules.executeAssignment(p.tokenbuf)
+		if err != nil {
+			p.basicErrorAtToken(err.what, err.where)
+		}
+		p.clear()
+		return parseTopLevel
+
+	default:
+		p.push(t)
+	}
+
+	return parseAssignment
+}
+
+// Everything up to ':' must be a target.
+func parseTargets(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenWord:
+		p.push(t)
+	case tokenColon:
+		p.push(t)
+		return parseAttributesOrPrereqs
+
+	default:
+		p.parseError("reading a rule's targets",
+			"filename or pattern", t)
+	}
+
+	return parseTargets
+}
+
+// Consume one or more strings followed by a first ':'.
+func parseAttributesOrPrereqs(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		return parseRecipe
+	case tokenColon:
+		p.push(t)
+		return parsePrereqs
+	case tokenWord:
+		p.push(t)
+	default:
+		p.parseError("reading a rule's attributes or prerequisites",
+			"an attribute, pattern, or filename", t)
+	}
+
+	return parseAttributesOrPrereqs
+}
+
+// Targets and attributes and the second ':' have been consumed.
+func parsePrereqs(p *parser, t token) parserStateFun {
+	switch t.typ {
+	case tokenNewline:
+		return parseRecipe
+	case tokenWord:
+		p.push(t)
+
+	default:
+		p.parseError("reading a rule's prerequisites",
+			"filename or pattern", t)
+	}
+
+	return parsePrereqs
+}
+
+// An entire rule has been consumed.
+func parseRecipe(p *parser, t token) parserStateFun {
+	// Assemble the rule!
+	r := rule{}
+
+	// find one or two colons
+	i := 0
+	for ; i < len(p.tokenbuf) && p.tokenbuf[i].typ != tokenColon; i++ {
+	}
+	j := i + 1
+	for ; j < len(p.tokenbuf) && p.tokenbuf[j].typ != tokenColon; j++ {
+	}
+
+	// rule has attributes
+	if j < len(p.tokenbuf) {
+		attribs := make([]string, 0)
+		for k := i + 1; k < j; k++ {
+			exparts := expand(p.tokenbuf[k].val, p.rules.vars, true)
+			attribs = append(attribs, exparts...)
+		}
+		err := r.parseAttribs(attribs)
+		if err != nil {
+			msg := fmt.Sprintf("while reading a rule's attributes expected an attribute but found \"%c\".", err.found)
+			p.basicErrorAtToken(msg, p.tokenbuf[i+1])
+		}
+
+		if r.attributes.regex {
+			r.ismeta = true
+		}
+	} else {
+		j = i
+	}
+
+	// targets
+	r.targets = make([]pattern, 0)
+	for k := 0; k < i; k++ {
+		exparts := expand(p.tokenbuf[k].val, p.rules.vars, true)
+		for i := range exparts {
+			targetstr := exparts[i]
+			r.targets = append(r.targets, pattern{spat: targetstr})
+
+			if r.attributes.regex {
+				rpat, err := regexp.Compile("^" + targetstr + "$")
+				if err != nil {
+					msg := fmt.Sprintf("invalid regular expression: %q", err)
+					p.basicErrorAtToken(msg, p.tokenbuf[k])
+				}
+				r.targets[len(r.targets)-1].rpat = rpat
+			} else {
+				idx := strings.IndexRune(targetstr, '%')
+				if idx >= 0 {
+					var left, right string
+					if idx > 0 {
+						left = regexp.QuoteMeta(targetstr[:idx])
+					}
+					if idx < len(targetstr)-1 {
+						right = regexp.QuoteMeta(targetstr[idx+1:])
+					}
+
+					patstr := fmt.Sprintf("^%s(.*)%s$", left, right)
+					rpat, err := regexp.Compile(patstr)
+					if err != nil {
+						msg := fmt.Sprintf("error compiling suffix rule. This is a bug. Error: %s", err)
+						p.basicErrorAtToken(msg, p.tokenbuf[k])
+					}
+					r.targets[len(r.targets)-1].rpat = rpat
+					r.targets[len(r.targets)-1].issuffix = true
+					r.ismeta = true
+				}
+			}
+		}
+	}
+
+	// prereqs
+	r.prereqs = make([]string, 0)
+	for k := j + 1; k < len(p.tokenbuf); k++ {
+		exparts := expand(p.tokenbuf[k].val, p.rules.vars, true)
+		r.prereqs = append(r.prereqs, exparts...)
+	}
+
+	if t.typ == tokenRecipe {
+		r.recipe = expandRecipeSigils(stripIndentation(t.val, t.col), p.rules.vars)
+	}
+
+	p.rules.add(r)
+	p.clear()
+
+	// the current token doesn't belong to this rule
+	if t.typ != tokenRecipe {
+		return parseTopLevel(p, t)
+	}
+
+	return parseTopLevel
+}
diff --git a/src/tool/mk/recipe.go b/src/tool/mk/recipe.go
new file mode 100644
index 0000000..7765fd8
--- /dev/null
+++ b/src/tool/mk/recipe.go
@@ -0,0 +1,208 @@
+// Various function for dealing with recipes.
+
+package mk
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+	"unicode/utf8"
+)
+
+// Try to unindent a recipe, so that it begins an column 0. (This is mainly for
+// recipes in python, or other indentation-significant languages.)
+func stripIndentation(s string, mincol int) string {
+	// trim leading whitespace
+	reader := bufio.NewReader(strings.NewReader(s))
+	output := ""
+	for {
+		line, err := reader.ReadString('\n')
+		col := 0
+		i := 0
+		for i < len(line) && col < mincol {
+			c, w := utf8.DecodeRuneInString(line[i:])
+			if strings.IndexRune(" \t\n", c) >= 0 {
+				col += 1
+				i += w
+			} else {
+				break
+			}
+		}
+		output += line[i:]
+
+		if err != nil {
+			break
+		}
+	}
+
+	return output
+}
+
+// Indent each line of a recipe.
+func printIndented(out io.Writer, s string, ind int) {
+	indentation := strings.Repeat(" ", ind)
+	reader := bufio.NewReader(strings.NewReader(s))
+	firstline := true
+	for {
+		line, err := reader.ReadString('\n')
+		if len(line) > 0 {
+			if !firstline {
+				io.WriteString(out, indentation)
+			}
+			io.WriteString(out, line)
+		}
+		if err != nil {
+			break
+		}
+		firstline = false
+	}
+}
+
+// Execute a recipe.
+func dorecipe(target string, u *node, e *edge, dryrun bool) bool {
+	vars := make(map[string][]string)
+	vars["target"] = []string{target}
+	if e.r.ismeta {
+		if e.r.attributes.regex {
+			for i := range e.matches {
+				vars[fmt.Sprintf("stem%d", i)] = e.matches[i : i+1]
+			}
+		} else {
+			vars["stem"] = []string{e.stem}
+		}
+	}
+
+	// TODO: other variables to set
+	// alltargets
+	// newprereq
+
+	prereqs := make([]string, 0)
+	for i := range u.prereqs {
+		if u.prereqs[i].r == e.r && u.prereqs[i].v != nil {
+			prereqs = append(prereqs, u.prereqs[i].v.name)
+		}
+	}
+	vars["prereq"] = prereqs
+
+	input := expandRecipeSigils(e.r.recipe, vars)
+	sh := "sh"
+	args := []string{}
+
+	if len(e.r.shell) > 0 {
+		sh = e.r.shell[0]
+		args = e.r.shell[1:]
+	}
+
+	mkPrintRecipe(target, input, e.r.attributes.quiet)
+
+	if dryrun {
+		return true
+	}
+
+	_, success := subprocess(
+		sh,
+		args,
+		input,
+		false)
+
+	return success
+}
+
+// Execute a subprocess (typically a recipe).
+//
+// Args:
+//   program: Program path or name located in PATH
+//   input: String piped into the program's stdin
+//   capture_out: If true, capture and return the program's stdout rather than echoing it.
+//
+// Returns
+//   (output, success)
+//   output is an empty string of catputer_out is false, or the collected output from the profram is true.
+//
+//   success is true if the exit code was 0 and false otherwise
+//
+func subprocess(program string,
+	args []string,
+	input string,
+	capture_out bool) (string, bool) {
+	program_path, err := exec.LookPath(program)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	proc_args := []string{program}
+	proc_args = append(proc_args, args...)
+
+	stdin_pipe_read, stdin_pipe_write, err := os.Pipe()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	attr := os.ProcAttr{Files: []*os.File{stdin_pipe_read, os.Stdout, os.Stderr}}
+
+	output := make([]byte, 0)
+	capture_done := make(chan bool)
+	if capture_out {
+		stdout_pipe_read, stdout_pipe_write, err := os.Pipe()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		attr.Files[1] = stdout_pipe_write
+
+		go func() {
+			buf := make([]byte, 1024)
+			for {
+				n, err := stdout_pipe_read.Read(buf)
+
+				if err == io.EOF && n == 0 {
+					break
+				} else if err != nil {
+					log.Fatal(err)
+				}
+
+				output = append(output, buf[:n]...)
+			}
+
+			capture_done <- true
+		}()
+	}
+
+	proc, err := os.StartProcess(program_path, proc_args, &attr)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	go func() {
+		_, err := stdin_pipe_write.WriteString(input)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		err = stdin_pipe_write.Close()
+		if err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	state, err := proc.Wait()
+
+	if attr.Files[1] != os.Stdout {
+		attr.Files[1].Close()
+	}
+
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// wait until stdout copying in finished
+	if capture_out {
+		<-capture_done
+	}
+
+	return string(output), state.Success()
+}
diff --git a/src/tool/mk/rules.go b/src/tool/mk/rules.go
new file mode 100644
index 0000000..6a246f6
--- /dev/null
+++ b/src/tool/mk/rules.go
@@ -0,0 +1,215 @@
+// Mkfiles are parsed into ruleSets, which as the name suggests, are sets of
+// rules with accompanying recipes, as well as assigned variables which are
+// expanding when evaluating rules and recipes.
+
+package mk
+
+import (
+	"fmt"
+	"regexp"
+	"unicode/utf8"
+)
+
+type attribSet struct {
+	delFailed       bool // delete targets when the recipe fails
+	nonstop         bool // don't stop if the recipe fails
+	forcedTimestamp bool // update timestamp whether the recipe does or not
+	nonvirtual      bool // a meta-rule that will only match files
+	quiet           bool // don't print the recipe
+	regex           bool // regular expression meta-rule
+	update          bool // treat the targets as if they were updated
+	virtual         bool // rule is virtual (does not match files)
+	exclusive       bool // don't execute concurrently with any other rule
+}
+
+// Error parsing an attribute
+type attribError struct {
+	found rune
+}
+
+// target and rereq patterns
+type pattern struct {
+	issuffix bool           // is a suffix '%' rule, so we should define $stem.
+	spat     string         // simple string pattern
+	rpat     *regexp.Regexp // non-nil if this is a regexp pattern
+}
+
+// Match a pattern, returning an array of submatches, or nil if it doesn'm
+// match.
+func (p *pattern) match(target string) []string {
+	if p.rpat != nil {
+		return p.rpat.FindStringSubmatch(target)
+	}
+
+	if target == p.spat {
+		return make([]string, 0)
+	}
+
+	return nil
+}
+
+// A single rule.
+type rule struct {
+	targets    []pattern // non-empty array of targets
+	attributes attribSet // rule attributes
+	prereqs    []string  // possibly empty prerequesites
+	shell      []string  // command used to execute the recipe
+	recipe     string    // recipe source
+	command    []string  // command attribute
+	ismeta     bool      // is this a meta rule
+	file       string    // file where the rule is defined
+	line       int       // line number on which the rule is defined
+}
+
+// Equivalent recipes.
+func (r1 *rule) equivRecipe(r2 *rule) bool {
+	if r1.recipe != r2.recipe {
+		return false
+	}
+
+	if len(r1.shell) != len(r2.shell) {
+		return false
+	}
+
+	for i := range r1.shell {
+		if r1.shell[i] != r2.shell[i] {
+			return false
+		}
+	}
+
+	return true
+}
+
+// A set of rules.
+type ruleSet struct {
+	vars  map[string][]string
+	rules []rule
+	// map a target to an array of indexes into rules
+	targetrules map[string][]int
+}
+
+// Read attributes for an array of strings, updating the rule.
+func (r *rule) parseAttribs(inputs []string) *attribError {
+	for i := 0; i < len(inputs); i++ {
+		input := inputs[i]
+		pos := 0
+		for pos < len(input) {
+			c, w := utf8.DecodeRuneInString(input[pos:])
+			switch c {
+			case 'D':
+				r.attributes.delFailed = true
+			case 'E':
+				r.attributes.nonstop = true
+			case 'N':
+				r.attributes.forcedTimestamp = true
+			case 'n':
+				r.attributes.nonvirtual = true
+			case 'Q':
+				r.attributes.quiet = true
+			case 'R':
+				r.attributes.regex = true
+			case 'U':
+				r.attributes.update = true
+			case 'V':
+				r.attributes.virtual = true
+			case 'X':
+				r.attributes.exclusive = true
+			case 'P':
+				if pos+w < len(input) {
+					r.command = append(r.command, input[pos+w:])
+				}
+				r.command = append(r.command, inputs[i+1:]...)
+				return nil
+
+			case 'S':
+				if pos+w < len(input) {
+					r.shell = append(r.shell, input[pos+w:])
+				}
+				r.shell = append(r.shell, inputs[i+1:]...)
+				return nil
+
+			default:
+				return &attribError{c}
+			}
+
+			pos += w
+		}
+	}
+
+	return nil
+}
+
+// Add a rule to the rule set.
+func (rs *ruleSet) add(r rule) {
+	rs.rules = append(rs.rules, r)
+	k := len(rs.rules) - 1
+	for i := range r.targets {
+		if r.targets[i].rpat == nil {
+			rs.targetrules[r.targets[i].spat] =
+				append(rs.targetrules[r.targets[i].spat], k)
+		}
+	}
+}
+
+func isValidVarName(v string) bool {
+	for i := 0; i < len(v); {
+		c, w := utf8.DecodeRuneInString(v[i:])
+		if i == 0 && !(isalpha(c) || c == '_') {
+			return false
+		} else if !(isalnum(c) || c == '_') {
+			return false
+		}
+		i += w
+	}
+	return true
+}
+
+func isdigit(c rune) bool {
+	return '0' <= c && c <= '9'
+}
+
+func isalpha(c rune) bool {
+	return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z')
+}
+
+func isalnum(c rune) bool {
+	return isalpha(c) || isdigit(c)
+}
+
+type assignmentError struct {
+	what  string
+	where token
+}
+
+// Parse and execute assignment operation.
+func (rs *ruleSet) executeAssignment(ts []token) *assignmentError {
+	assignee := ts[0].val
+	if !isValidVarName(assignee) {
+		return &assignmentError{
+			fmt.Sprintf("target of assignment is not a valid variable name: \"%s\"", assignee),
+			ts[0]}
+	}
+
+	// interpret tokens in assignment context
+	input := make([]string, 0)
+	for i := 1; i < len(ts); i++ {
+		if ts[i].typ != tokenWord || (i > 1 && ts[i-1].typ != tokenWord) {
+			if len(input) == 0 {
+				input = append(input, ts[i].val)
+			} else {
+				input[len(input)-1] += ts[i].val
+			}
+		} else {
+			input = append(input, ts[i].val)
+		}
+	}
+
+	// expanded variables
+	vals := make([]string, 0)
+	for i := 0; i < len(input); i++ {
+		vals = append(vals, expand(input[i], rs.vars, true)...)
+	}
+
+	rs.vars[assignee] = vals
+	return nil
+}