format.go

@@ -204,8 +204,7 @@ type arm struct {
 	head        string
 	writtenHead string // head as written, sigil included
 	tail        []string
-	levels      []string // the path at each level the tail passes through, the head first
-	path        string   // head and tail, the one path every way of writing this read shares
+	levels      []pickKey // the key of each level the steps pass, from the head they start at to the leaf
 	steps       []pathStep
 	leaves      []node // every node the path may land on, one per variant it passes
 	kind        armKind
@@ -230,7 +229,7 @@ func splitArm(name string, refs map[string]refBinding) arm {
 			if linked {
 				head = b.head
 			}
-			return arm{spelling: name, head: head, path: head}
+			return arm{spelling: name, head: head, levels: []pickKey{pickKey(head)}}
 		}
 		sigil, rest, _ := grammar.RefShape(name) // resolveLink proved it, and took b.tail as a suffix of its segments
 		written, _ := grammar.SplitPath(rest)
@@ -238,19 +237,27 @@ func splitArm(name string, refs map[string]refBinding) arm {
 	}
 	segs, err := grammar.SplitPath(name)
 	if err != nil || len(segs) == 1 {
-		return arm{spelling: name, head: name, path: name}
+		return arm{spelling: name, head: name, levels: []pickKey{pickKey(name)}}
 	}
 	return pathArm(name, segs[0], segs[0], segs[1:])
 }
 
 func pathArm(name, head, writtenHead string, segs []string) arm {
-	levels := []string{head}
-	for i := 0; i < len(segs)-1; i++ {
-		levels = append(levels, head+"."+strings.Join(segs[:i+1], "."))
-	}
-	return arm{spelling: name, head: head, writtenHead: writtenHead, tail: segs, levels: levels, path: head + "." + strings.Join(segs, ".")}
+	return arm{spelling: name, head: head, writtenHead: writtenHead, tail: segs, levels: levelKeys(append([]string{head}, segs...), 1)}
 }
 
+// levelKeys is the key of each level path passes, the first after its first from segments.
+func levelKeys(path []string, from int) []pickKey {
+	levels := make([]pickKey, len(path)-from+1)
+	for i := range levels {
+		levels[i] = pickKey(grammar.JoinSegments(path[:from+i]))
+	}
+	return levels
+}
+
+// key is the key of the leaf a lands on, the one key every way of writing this read shares.
+func (a arm) key() pickKey { return a.levels[len(a.levels)-1] }
+
 func checkSegments(a arm) error {
 	if len(a.tail) == 0 {
 		return nil
@@ -340,10 +347,6 @@ func (t *template) compileArm(name string, targets map[*nameBinding]nameTarget)
 	}
 	w := compilePath(target.head, full)
 	a.kind, a.named, a.steps, a.leaves = namedRead, b, w.steps, w.leaves
-	a.levels = make([]string, len(full)+1)
-	for i := range a.levels {
-		a.levels[i] = grammar.JoinSegments(full[:i])
-	}
-	a.path = grammar.JoinSegments(full)
+	a.levels = levelKeys(full, 0)
 	return a, nil
 }

link.go

@@ -57,7 +57,7 @@ type nameTarget struct {
 // target, the keys its reads address, and its reads.
 type linkedNames struct {
 	targets   map[*nameBinding]nameTarget
-	addressed map[*nameBinding]map[string]string
+	addressed map[*nameBinding]map[pickKey]string
 	uses      map[*nameBinding][]nameUse
 }
 
@@ -117,15 +117,15 @@ func nameTargets(ts []linkSite) map[*nameBinding]nameTarget {
 
 // addressedKeys is every key the reads of each name in ts land on or pass, from the name, with the
 // spelling of the first read reaching it.
-func addressedKeys(ts []linkSite, targets map[*nameBinding]nameTarget) map[*nameBinding]map[string]string {
-	keys := map[*nameBinding]map[string]string{}
+func addressedKeys(ts []linkSite, targets map[*nameBinding]nameTarget) map[*nameBinding]map[pickKey]string {
+	keys := map[*nameBinding]map[pickKey]string{}
 	for _, s := range ts {
 		for _, r := range namedReads(s.t) {
 			b := r.a.named
 			if keys[b] == nil {
-				keys[b] = map[string]string{}
+				keys[b] = map[pickKey]string{}
 			}
-			for _, key := range append(r.a.levels[len(targets[b].tail):], r.a.path) {
+			for _, key := range r.a.levels[len(targets[b].tail):] {
 				if _, seen := keys[b][key]; !seen {
 					keys[b][key] = r.a.spelling
 				}

name.go

@@ -33,7 +33,7 @@ type nameBinding struct {
 	nameTarget
 	// addressed is every key a read of the name lands on or passes, the spelling of the
 	// first read reaching it beside it; a pick keeps the draws at these keys, and only these.
-	addressed map[string]string
+	addressed map[pickKey]string
 }
 
 // nameUse is one read of a name: the path it reads into the name, "" for the name itself; the

namefence.go

@@ -28,7 +28,7 @@ func checkNameReads(label string, t *template, names linkedNames) error {
 			return fmt.Errorf("%s: token {%s}: name %q is read inside %q, the field bound to it; read the name outside that field", label, r.o.Body, b.name, b.ref)
 		}
 		for _, leaf := range r.a.leaves {
-			if err := checkOnce(names.addressed[b], r.a.spelling, leaf, r.a.path); err != nil {
+			if err := checkOnce(names.addressed[b], r.a.spelling, leaf, r.a.key()); err != nil {
 				return fmt.Errorf("%s: token {%s}: %w", label, r.o.Body, err)
 			}
 		}
@@ -122,7 +122,7 @@ func calcReads(spelling string) bool {
 
 // checkOnce walks n, rendering at key under a pick, into each level a read of the name addresses:
 // the keys of addressed.
-func checkOnce(addressed map[string]string, read string, n node, key string) error {
+func checkOnce(addressed map[pickKey]string, read string, n node, key pickKey) error {
 	switch n := n.(type) {
 	case *choice:
 		for _, item := range n.items {
@@ -136,7 +136,7 @@ func checkOnce(addressed map[string]string, read string, n node, key string) err
 	return nil
 }
 
-func checkTemplateOnce(addressed map[string]string, read string, t *template, key string) error {
+func checkTemplateOnce(addressed map[pickKey]string, read string, t *template, key pickKey) error {
 	reads := map[string]int{}
 	var into []arm
 	for _, o := range t.compiled.ops {
@@ -144,20 +144,20 @@ func checkTemplateOnce(addressed map[string]string, read string, t *template, ke
 			if grammar.IsRef(a.head) || a.kind == namedRead {
 				continue
 			}
-			if _, kept := addressed[join(key, a.path)]; kept {
+			if _, kept := addressed[key.under(a.key())]; kept {
 				into = append(into, a)
 			}
 			reads[a.head]++
 		}
 	}
 	for _, head := range sortedNames(reads) {
-		if by, kept := addressed[join(key, head)]; kept && reads[head] > 1 {
+		if by, kept := addressed[key.under(pickKey(head))]; kept && reads[head] > 1 {
 			return fmt.Errorf("{%s} renders field %q twice, so {%s} cannot say which draw it reads; drop {%s} or {%s}", read, head, by, read, by)
 		}
 	}
 	for _, a := range into {
 		for _, leaf := range a.leaves {
-			if err := checkOnce(addressed, read, leaf, join(key, a.path)); err != nil {
+			if err := checkOnce(addressed, read, leaf, key.under(a.key())); err != nil {
 				return err
 			}
 		}

path.go

@@ -263,7 +263,7 @@ func probePath(n node, tail []string, steps []pathStep) ([]pathStep, error) {
 // For a read through a name, memo keeps the variant drawn at each of levels, so paths sharing a
 // prefix share it. It returns the leaf and the pins its row is in: a step down after a step up draws
 // afresh, into pins of its own, which memo shares with every path stepping down there.
-func drawSteps(s *drawstate.State, n node, steps []pathStep, pins *pinSet, memo *drawMemo, levels []string) (node, *pinSet) {
+func drawSteps(s *drawstate.State, n node, steps []pathStep, pins *pinSet, memo *drawMemo, levels []pickKey) (node, *pinSet) {
 	var climbed *rowsTable
 	for _, st := range steps {
 		if c, ok := n.(*choice); ok {
@@ -313,7 +313,7 @@ func (t *table) drawStep(s *drawstate.State, st pathStep, pins *pinSet) node {
 	panic(invariant.Broken("drawStep has no case for step kind %d", st.kind))
 }
 
-func drawVariant(s *drawstate.State, c *choice, memo *drawMemo, levels []string, at int) node {
+func drawVariant(s *drawstate.State, c *choice, memo *drawMemo, levels []pickKey, at int) node {
 	if memo == nil {
 		return resolveChoice(s, c)
 	}

pick.go

@@ -5,6 +5,20 @@ import (
 	"github.com/larvit/fejkdata/internal/invariant"
 )
 
+// pickKey is where a level sits in a named pick: its path from the head the name's target starts
+// at, which is "". A fresh read keys its levels from its own head until readUnder keys them under
+// the pick.
+type pickKey string
+
+// under is the key of rel, a fresh read's key, in what renders at k. It never returns k itself: k
+// is sc.pickAt, and a memo keeping it would move every render's scope to the heap.
+func (k pickKey) under(rel pickKey) pickKey {
+	if k == "" {
+		return rel
+	}
+	return k + "." + rel
+}
+
 // namedPick is one draw of a name: the variant drawn at each level a read of it addresses, the
 // value each read there produced, keyed by the path from the name, and the table rows they
 // pinned.
@@ -19,15 +33,15 @@ type namedPick struct {
 // twice reads one value; the frames a read opens for the name scopes around where it lands
 // (enter); and the rows drawn by each step down after a "..", by level.
 type drawMemo struct {
-	variant       map[string]node
-	value         map[string]readValue
+	variant       map[pickKey]node
+	value         map[pickKey]readValue
 	enteredFrames map[*nameScope]*pickFrame
-	steppedDown   map[string]*pinSet
+	steppedDown   map[pickKey]*pinSet
 }
 
 // stepDownPins is the pins a path steps down into after stepping up to t: kept in m where there
 // is one, so every path stepping down there reads one draw.
-func (m *drawMemo) stepDownPins(pins *pinSet, t *rowsTable, levels []string, at int) *pinSet {
+func (m *drawMemo) stepDownPins(pins *pinSet, t *rowsTable, levels []pickKey, at int) *pinSet {
 	if m == nil {
 		return pins.Above(t)
 	}
@@ -35,7 +49,7 @@ func (m *drawMemo) stepDownPins(pins *pinSet, t *rowsTable, levels []string, at
 	if !ok {
 		p = pins.Above(t)
 		if m.steppedDown == nil {
-			m.steppedDown = map[string]*pinSet{}
+			m.steppedDown = map[pickKey]*pinSet{}
 		}
 		m.steppedDown[levels[at]] = p
 	}
@@ -153,15 +167,15 @@ func readName(s *drawstate.State, sc renderScope, a arm) readValue {
 		panic(invariant.Broken("name %q is read where no frame of its scope renders", a.named.name))
 	}
 	p := &f.picks[a.named.index]
-	if r, done := p.memo.value[a.path]; done {
+	if r, done := p.memo.value[a.key()]; done {
 		return r
 	}
-	leaf, pins := p.draw(s, a.named.head, a.steps, a.levels, a.path)
+	leaf, pins := p.draw(s, a.named.head, a.steps, a.levels)
 	if a.named.bindsField() {
-		return p.renderAt(s, leaf, pins, a.path, sc)
+		return p.renderAt(s, leaf, pins, a.key(), sc)
 	}
 	sc, mark := sc.enter(leaf, &p.memo)
-	r := p.renderAt(s, leaf, pins, a.path, sc)
+	r := p.renderAt(s, leaf, pins, a.key(), sc)
 	sc.frames.pop(mark)
 	return r
 }
@@ -176,63 +190,54 @@ func (sc renderScope) drawRowOf(s *drawstate.State, t *table) int {
 
 // keeps reports whether a read of sc's name addresses the level a starts at.
 func (sc renderScope) keeps(a arm) bool {
-	_, kept := sc.pick.named.addressed[underKey(sc.pickKey, a.head)]
+	_, kept := sc.pick.named.addressed[sc.pickAt.under(a.levels[0])]
 	return kept
 }
 
-// readUnder reads a of t, which renders as part of the pick sc.pick at sc.pickKey, where a read of
-// the name addresses it: once per pick, by its path from the name.
+// readUnder reads a of t, which renders as part of the pick sc.pick at sc.pickAt, where a read of
+// the name addresses it: once per pick, by its key in the pick.
 func readUnder(s *drawstate.State, t *template, sc renderScope, a arm) readValue {
-	p, key := sc.pick, underKey(sc.pickKey, a.path)
+	p, key := sc.pick, sc.pickAt.under(a.key())
 	if r, done := p.memo.value[key]; done {
 		return r
 	}
-	levels := make([]string, len(a.levels))
+	levels := make([]pickKey, len(a.levels))
 	for i, l := range a.levels {
-		levels[i] = underKey(sc.pickKey, l)
+		levels[i] = sc.pickAt.under(l)
 	}
-	leaf, pins := p.draw(s, t.head(a.head), a.steps, levels, key)
+	leaf, pins := p.draw(s, t.head(a.head), a.steps, levels)
 	return p.renderAt(s, leaf, pins, key, sc)
 }
 
-// underKey is the key of path under the pick key prefix. It never returns prefix itself: prefix is
-// sc.pickKey, and a memo keeping it would move every render's scope to the heap.
-func underKey(prefix, path string) string {
-	if prefix == "" {
-		return path
-	}
-	return prefix + "." + path
-}
-
-// draw draws the path key names under p, its variant at key kept too, returning the leaf and the
-// pins its row is in.
-func (p *namedPick) draw(s *drawstate.State, head node, steps []pathStep, levels []string, key string) (node, *pinSet) {
+// draw draws the path from head under p, keeping the variant drawn at each of levels, the leaf's
+// last, and returns the leaf and the pins its row is in.
+func (p *namedPick) draw(s *drawstate.State, head node, steps []pathStep, levels []pickKey) (node, *pinSet) {
 	leaf, pins := drawSteps(s, head, steps, &p.pins, &p.memo, levels)
 	if c, isChoice := leaf.(*choice); isChoice {
-		leaf = p.memo.variantOf(s, c, key)
+		leaf = p.memo.variantOf(s, c, levels[len(levels)-1])
 	}
 	return leaf, pins
 }
 
 // renderAt renders leaf, drawn at key into pins, as part of p, and keeps what it rendered.
-func (p *namedPick) renderAt(s *drawstate.State, leaf node, pins *pinSet, key string, sc renderScope) readValue {
+func (p *namedPick) renderAt(s *drawstate.State, leaf node, pins *pinSet, key pickKey, sc renderScope) readValue {
 	sc = sc.at(leaf, pins)
-	sc.pick, sc.pickKey = p, key
+	sc.pick, sc.pickAt = p, key
 	r := renderLeaf(s, leaf, sc)
 	if p.memo.value == nil {
-		p.memo.value = map[string]readValue{}
+		p.memo.value = map[pickKey]readValue{}
 	}
 	p.memo.value[key] = r
 	return r
 }
 
 // variantOf is the variant of c drawn at level, drawn now where none was.
-func (m *drawMemo) variantOf(s *drawstate.State, c *choice, level string) node {
+func (m *drawMemo) variantOf(s *drawstate.State, c *choice, level pickKey) node {
 	n, drew := m.variant[level]
 	if !drew {
 		n = resolveChoice(s, c)
 		if m.variant == nil {
-			m.variant = map[string]node{}
+			m.variant = map[pickKey]node{}
 		}
 		m.variant[level] = n
 	}

record.go

@@ -300,4 +300,4 @@ func renderRecord(s *drawstate.State, t *template, sc renderScope) *Record {
 }
 
 // wholeLevels is the levels of a read of a whole name, as compileArm compiles {n}.
-var wholeLevels = []string{""}
+var wholeLevels = []pickKey{""}

render.go

@@ -146,7 +146,7 @@ func expand(s *drawstate.State, t *template, sc renderScope) string {
 // a level that a read of the name being rendered addresses; every other read draws afresh, so
 // {word} {word} draws twice and {p.a} {p.b} reads two draws of p.
 // A fresh read clears sc.pick. Kept, a read nested in the fresh one would key the pick's memo by
-// sc.pickKey, the path from the name to what the pick renders, and share a value with a different
+// sc.pickAt, where in the pick it renders, and share a value with a different
 // node at that path.
 func readField(s *drawstate.State, t *template, sc renderScope, a arm) readValue {
 	switch {

scope.go

@@ -18,10 +18,9 @@ type renderScope struct {
 	// base is the depth of the frame stack when the read rendering the category entered it,
 	// below which no frame is the category's.
 	base int
-	// pick is the named pick being rendered, nil outside one; pickKey is the path from the name
-	// to what renders.
+	// pick is the named pick being rendered, nil outside one; pickAt is where in it this renders.
 	pick   *namedPick
-	pickKey string
+	pickAt pickKey
 }
 
 type renderedRow struct {

todo.md

@@ -76,7 +76,6 @@
 | 91 | 0.1.0 |  | **Accept a path through a name as a `calc` operand, so `{/misc.coordinate as c}{c}: {calc(c.lat * 60)}` computes from the coordinate `{c}` prints.** | 3 | 4 | 6 | 7 | 4.1, 5.3 | 19.9 |
 | 89 | 0.1.0 |  | **Fail `New` without `WithSeed`, naming the option, and seed the CLI from the system.** | 3 | 3 | 6 | 7 | 10.1 | 16.0 |
 | 127 | 0.1.0 |  | **Give a Swedish street only postal codes whose delivery digit means street or rural delivery, dropping codes whose delivery digit is 9, or record why they stay.** | 3 | 3 | 4 | 6 | 4 | 14.4 |
-| 118 | 0.1.0 |  | **Give a pick key one type, so `pathArm`, `compileArm`, `addressedKeys`, `keeps`, `readUnder` and `checkTemplateOnce` spell it one way, and `arm.levels` start at the same level for a fresh read and a named read.** | 5 | 5 | 2 | 9 | 3.2, 3.3 | 13.9 |
 | 110 | 0.1.0 |  | **Refuse an empty segment in a path `Fake`, `FakeRecord` and the CLI take, as a reference does: `sv_SE.person.` reports `path has an empty segment`.** | 1 | 1 | 3 | 6 | 6 | 13.8 |
 | 120 | 0.1.0 |  | **Rename the engine's overloaded nouns, so `scope`, `binding`, `link`, `pick` and `head` each name one thing.** | 2 | 4 | 1 | 8 | 3.3 | 13.4 |
 | 123 | 0.1.0 |  | **Name the name fences by what they refuse, and state each rule at `checkOnce`, `checkTemplateOnce` and `checkUses`, so they read without the README's Names list.** | 1 | 2 | 1 | 7 | 3.4, 3.3 | 13.1 |
@@ -264,10 +263,6 @@ Goal 10.1 has the caller supply the seed, and today `New` without `WithSeed` see
 
 `docs/research/research-geo-se.md` reads delivery digit 0 or 1 as boxes, 2–4 and 6–7 as street, 5 as rural, 8 as reply mail and 9 as competitions or temporary, with exceptions in big cities. `street_delivery` drops 0, 1 and 8 and keeps 9. The panel of 2026-10-05 found it; whether a shipped street carries a 9 code is unchecked.
 
-### 118. Give a pick key one type, so `pathArm`, `compileArm`, `addressedKeys`, `keeps`, `readUnder` and `checkTemplateOnce` spell it one way, and `arm.levels` start at the same level for a fresh read and a named read.
-
-Eight of the nine seats in the panel of 2026-10-05 named the key convention hardest after the named-pick read path itself. A fresh read's `levels` start at the head, `[head, head.a, …]`, while `compileArm` builds a named read's from the name, `["", a, a.b, …]`, so `arm.levels`' comment holds only for fresh reads. `addressedKeys` slices off the target's tail and `readUnder` re-prefixes with `underKey`; no type ties them. Keep the key a string, so the allocation gate holds.
-
 ### 110. Refuse an empty segment in a path `Fake`, `FakeRecord` and the CLI take, as a reference does: `sv_SE.person.` reports `path has an empty segment`.
 
 Today `fejkdata 'sv_SE.person.'` reports `no field ""`, while `{/sv_SE.person.}` reports `path has an empty segment`. `grammar.CheckSegments` is the check a reference, a sibling path and a step up `..` run.