Move the seeded randomness and the {seq()} counters into internal/drawstate

builtins.go

@@ -7,6 +7,8 @@ import (
 	"math"
 	"strconv"
 	"strings"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // maxLen caps sample output lengths (hex, nanoid, base64, digits, upper, lower)
@@ -40,19 +42,19 @@ var builtins = withTransforms(map[string]builtin{
 	"lower": {arity: 1, checkArgs: posIntArg, prep: chars("abcdefghijklmnopqrstuvwxyz")},
 	"base64": {arity: 1, checkArgs: posIntArg, prep: func(a []string) callFn {
 		n := atoi(a[0])
-		return func(s *generatorState, _ string, _ []string) string {
+		return func(s *drawstate.State, _ string, _ []string) string {
 			return base64.StdEncoding.EncodeToString(randBytes(s, n))
 		}
 	}},
 	"int": {arity: 2, checkArgs: intRangeArgs, prep: func(a []string) callFn {
 		lo, span := atoi(a[0]), atoi(a[1])-atoi(a[0])+1
-		return func(s *generatorState, _ string, _ []string) string { return strconv.Itoa(lo + s.IntN(span)) }
+		return func(s *drawstate.State, _ string, _ []string) string { return strconv.Itoa(lo + s.IntN(span)) }
 	}, prints: DataTypeInteger, proveNumber: func(token string, prints DataType, a []string) proven {
 		return printing(token, prints, bounded(float64(atoi(a[0])), float64(atoi(a[1])), true))
 	}},
 	"float": {arity: 3, checkArgs: floatArgs, prep: func(a []string) callFn {
 		lo, hi, dp := atof(a[0]), atof(a[1]), atoi(a[2])
-		return func(s *generatorState, _ string, _ []string) string {
+		return func(s *drawstate.State, _ string, _ []string) string {
 			return formatFloat(lo+s.Float64()*(hi-lo), dp)
 		}
 	}, prints: DataTypeNumber, proveNumber: func(token string, _ DataType, a []string) proven {
@@ -60,7 +62,7 @@ var builtins = withTransforms(map[string]builtin{
 	}},
 	"iban": {arity: 1, checkArgs: ibanArg, prep: func(a []string) callFn {
 		cc := a[0]
-		return func(s *generatorState, _ string, _ []string) string { return iban(s, cc) }
+		return func(s *drawstate.State, _ string, _ []string) string { return iban(s, cc) }
 	}},
 	"date": {arity: -1, checkArgs: dateArgs, prep: datePrep},
 	"time": {arity: -1, checkArgs: timeArg, prep: timePrep},
@@ -73,8 +75,8 @@ var builtins = withTransforms(map[string]builtin{
 		if len(a) == 1 {
 			key = a[0]
 		}
-		return func(s *generatorState, _ string, _ []string) string {
+		return func(s *drawstate.State, _ string, _ []string) string {
-			return strconv.FormatUint(s.next(key), 10)
+			return strconv.FormatUint(s.Next(key), 10)
 		}
 	}, prints: DataTypeInteger, proveNumber: func(token string, prints DataType, _ []string) proven {
 		return printing(token, prints, bounded(1, math.MaxInt64, true))
@@ -86,18 +88,18 @@ var builtins = withTransforms(map[string]builtin{
 // sample of n characters drawn from an alphabet.
 func derive(f func(emitted string) string) func([]string) callFn {
 	return func([]string) callFn {
-		return func(_ *generatorState, emitted string, _ []string) string { return f(emitted) }
+		return func(_ *drawstate.State, emitted string, _ []string) string { return f(emitted) }
 	}
 }
 func sample(f func(rng) string) func([]string) callFn {
 	return func([]string) callFn {
-		return func(s *generatorState, _ string, _ []string) string { return f(s) }
+		return func(s *drawstate.State, _ string, _ []string) string { return f(s) }
 	}
 }
 func chars(alphabet string) func([]string) callFn {
 	return func(a []string) callFn {
 		n := atoi(a[0])
-		return func(s *generatorState, _ string, _ []string) string { return randChars(s, n, alphabet) }
+		return func(s *drawstate.State, _ string, _ []string) string { return randChars(s, n, alphabet) }
 	}
 }
 

calc.go

@@ -7,6 +7,8 @@ import (
 	"strconv"
 	"strings"
 	"unicode"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // calcNode is a parsed expression node. It evaluates over the operand values expand
@@ -235,7 +237,7 @@ func calcPrep(args []string) callFn {
 	}
 	placed := indexVars(expr, at)
 	dp := calcDecimals(args)
-	return func(_ *generatorState, _ string, operands []string) string {
+	return func(_ *drawstate.State, _ string, operands []string) string {
 		return formatFloat(placed.eval(operands), dp)
 	}
 }

fejkdata.go

@@ -6,11 +6,12 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
-	"math/rand/v2"
 	"os"
 	"reflect"
 	"sort"
 	"sync"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // MaxRepeat caps a repeat, and caps the renders nested repeats multiply to along
@@ -26,27 +27,15 @@ var ErrNoData = errors.New("no data: WithoutShippedData needs at least one WithD
 // It is safe for concurrent use; a seeded sequence is reproducible only when drawn
 // from one goroutine.
 type Generator struct {
-	// mu guards rand, records, structs and root, which gains a shipped category on the
+	// mu guards draws, records, structs and root, which gains a shipped category on the
 	// first call reaching it.
 	mu      sync.Mutex
-	rand    *generatorState
+	draws   *drawstate.State
 	root    folder // the categories as the node a path walks from, owned here so a walk allocates none
 	records map[node]recordShape
 	structs map[reflect.Type]structResult
 }
 
-// generatorState is one generator's draw state, kept across its renders: the seeded rng plus
-// the {seq()} counters.
-type generatorState struct {
-	*rand.Rand
-	counters map[string]uint64
-}
-
-func (s *generatorState) next(key string) uint64 {
-	s.counters[key]++
-	return s.counters[key]
-}
-
 type config struct {
 	seed    uint64
 	seeded  bool
@@ -97,11 +86,11 @@ func New(opts ...Option) (*Generator, error) {
 	if err != nil {
 		return nil, fmt.Errorf("fejkdata: %w", err)
 	}
-	rng, err := newRand(c.seed, c.seeded)
+	seed, err := c.drawSeed()
 	if err != nil {
 		return nil, fmt.Errorf("fejkdata: %w", err)
 	}
-	return &Generator{rand: rng, root: root}, nil
+	return &Generator{draws: drawstate.New(seed), root: root}, nil
 }
 
 // load is the tree New starts from.
@@ -231,18 +220,16 @@ func join(prefix, name string) string {
 // randomBytes seeds an unseeded generator.
 var randomBytes = crand.Read
 
-func newRand(seed uint64, seeded bool) (*generatorState, error) {
+// drawSeed is the seed WithSeed gave, or one read from the system's entropy.
-	var r *rand.Rand
+func (c config) drawSeed() (uint64, error) {
-	if seeded {
+	if c.seeded {
-		r = rand.New(rand.NewPCG(seed, seed^0x9e3779b97f4a7c15))
+		return c.seed, nil
-	} else {
-		var b [16]byte
-		if _, err := randomBytes(b[:]); err != nil {
-			return nil, fmt.Errorf("seeding from crypto/rand: %w", err)
-		}
-		r = rand.New(rand.NewPCG(binary.LittleEndian.Uint64(b[:8]), binary.LittleEndian.Uint64(b[8:])))
 	}
-	return &generatorState{Rand: r, counters: map[string]uint64{}}, nil
+	var b [8]byte
+	if _, err := randomBytes(b[:]); err != nil {
+		return 0, fmt.Errorf("seeding from crypto/rand: %w", err)
+	}
+	return binary.LittleEndian.Uint64(b[:]), nil
 }
 
 func internalError(format string, a ...any) string {

format.go

@@ -3,6 +3,8 @@ package fejkdata
 import (
 	"fmt"
 	"strings"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // scanUnit is one unit of a scanned format string: a literal rune or the body of a
@@ -119,7 +121,7 @@ func parseFormat(format string) ([]formatToken, error) {
 }
 
 // builtin is a format-string function invoked as {name(args)}. It receives the
-// generatorState, the output emitted so far in the current expansion (for derivations
+// draw state, the output emitted so far in the current expansion (for derivations
 // such as a checksum over preceding digits), and the values of the operands it named
 // (calc and the transforms name them). All must stay pure over (rng, emitted, args) so
 // seeded output is reproducible; seq advances per-generator counter state, which is
@@ -461,7 +463,7 @@ func checkSegments(a arm) error {
 // callFn is a builtin prepared for one call site: its args already parsed. It reads the
 // output emitted so far in the current expansion (a derivation's payload) and the
 // values of the operands it named, which expand read for it.
-type callFn func(s *generatorState, emitted string, operands []string) string
+type callFn func(s *drawstate.State, emitted string, operands []string) string
 
 // op is one compiled unit of a format string: a literal run, a name read,
 // or a builtin already prepared with its args.

inline.go

@@ -20,7 +20,7 @@ type Template struct {
 func (t *Template) Fake() string {
 	t.g.mu.Lock()
 	defer t.g.mu.Unlock()
-	return renderOnce(t.g.rand, t.n)
+	return renderOnce(t.g.draws, t.n)
 }
 
 // NewTemplate compiles an inline template — a format string or a JSON value — and

internal/drawstate/drawstate.go

@@ -0,0 +1,22 @@
+// Package drawstate holds what a generator draws through: the seeded randomness and the
+// {seq()} counters.
+package drawstate
+
+import "math/rand/v2"
+
+// State is one generator's draw state, kept across its renders.
+type State struct {
+	*rand.Rand
+	counters map[string]uint64
+}
+
+// New builds the state a seed reproduces.
+func New(seed uint64) *State {
+	return &State{Rand: rand.New(rand.NewPCG(seed, seed^0x9e3779b97f4a7c15)), counters: map[string]uint64{}}
+}
+
+// Next advances the counter key names, the one {seq()} or {seq(key)} reads, and returns it.
+func (s *State) Next(key string) uint64 {
+	s.counters[key]++
+	return s.counters[key]
+}

layout.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"strings"
 	"time"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 const dayLayout = "2006-01-02"
@@ -135,13 +137,13 @@ func datePrep(a []string) callFn {
 		panic(internalError("builtin arg %q reached prep unvalidated: %v", a[1], err))
 	}
 	layout, start, span := layoutOf(a[2]), from.Unix(), int(to.Unix()-from.Unix())+86400
-	return func(s *generatorState, _ string, _ []string) string {
+	return func(s *drawstate.State, _ string, _ []string) string {
 		return time.Unix(start+int64(s.IntN(span)), 0).UTC().Format(layout)
 	}
 }
 func timePrep(a []string) callFn {
 	layout := layoutOf(a[0])
-	return func(s *generatorState, _ string, _ []string) string {
+	return func(s *drawstate.State, _ string, _ []string) string {
 		return time.Unix(int64(s.IntN(86400)), 0).UTC().Format(layout)
 	}
 }

path.go

@@ -3,6 +3,8 @@ package fejkdata
 import (
 	"fmt"
 	"strings"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // splitPath splits a dotted path into segments, a selector — [key or name] after a
@@ -430,7 +432,7 @@ 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 *generatorState, 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 []string) (node, *pinSet) {
 	var climbed *table
 	for _, st := range steps {
 		if c, ok := n.(*choice); ok {
@@ -458,7 +460,7 @@ func drawSteps(s *generatorState, n node, steps []pathStep, pins *pinSet, memo *
 	return n, pins
 }
 
-func (t *table) drawStep(s *generatorState, st pathStep, pins *pinSet) node {
+func (t *table) drawStep(s *drawstate.State, st pathStep, pins *pinSet) node {
 	switch st.kind {
 	case stepSelect:
 		if err := pins.pinRow(t, st.row); err != nil {
@@ -480,7 +482,7 @@ func (t *table) drawStep(s *generatorState, st pathStep, pins *pinSet) node {
 	panic(internalError("drawStep has no case for step kind %d", st.kind))
 }
 
-func drawVariant(s *generatorState, c *choice, memo *drawMemo, levels []string, at int) node {
+func drawVariant(s *drawstate.State, c *choice, memo *drawMemo, levels []string, at int) node {
 	if memo == nil {
 		return resolveChoice(s, c)
 	}

pick.go

@@ -1,5 +1,7 @@
 package fejkdata
 
+import "github.com/larvit/fejkdata/internal/drawstate"
+
 // 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.
@@ -135,7 +137,7 @@ func (sc renderScope) frameOf(scope *nameScope) *pickFrame {
 	return nil
 }
 
-func readName(s *generatorState, sc renderScope, a arm) readValue {
+func readName(s *drawstate.State, sc renderScope, a arm) readValue {
 	f := sc.frameOf(a.named.scope)
 	if f == nil {
 		panic(internalError("name %q is read where no frame of its scope renders", a.named.name))
@@ -155,7 +157,7 @@ func readName(s *generatorState, sc renderScope, a arm) readValue {
 }
 
 // drawRowOf draws the row a render of t reads: inside the pick's rows where t renders as part of one.
-func (sc renderScope) drawRowOf(s *generatorState, t *table) int {
+func (sc renderScope) drawRowOf(s *drawstate.State, t *table) int {
 	if sc.pick != nil {
 		return t.drawIn(s, &sc.pick.pins)
 	}
@@ -170,7 +172,7 @@ func (sc renderScope) keeps(a arm) bool {
 
 // 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.
-func readUnder(s *generatorState, t *template, sc renderScope, a arm) readValue {
+func readUnder(s *drawstate.State, t *template, sc renderScope, a arm) readValue {
 	p, key := sc.pick, underKey(sc.pickKey, a.path)
 	if r, done := p.memo.value[key]; done {
 		return r
@@ -194,7 +196,7 @@ func underKey(prefix, path string) string {
 
 // 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 *generatorState, head node, steps []pathStep, levels []string, key string) (node, *pinSet) {
+func (p *namedPick) draw(s *drawstate.State, head node, steps []pathStep, levels []string, key string) (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)
@@ -203,7 +205,7 @@ func (p *namedPick) draw(s *generatorState, head node, steps []pathStep, levels
 }
 
 // renderAt renders leaf, drawn at key into pins, as part of p, and keeps what it rendered.
-func (p *namedPick) renderAt(s *generatorState, leaf node, pins *pinSet, key string, sc renderScope) readValue {
+func (p *namedPick) renderAt(s *drawstate.State, leaf node, pins *pinSet, key string, sc renderScope) readValue {
 	sc = sc.at(leaf, pins)
 	sc.pick, sc.pickKey = p, key
 	r := renderLeaf(s, leaf, sc)
@@ -215,7 +217,7 @@ func (p *namedPick) renderAt(s *generatorState, leaf node, pins *pinSet, key str
 }
 
 // variantOf is the variant of c drawn at level, drawn now where none was.
-func (m *drawMemo) variantOf(s *generatorState, c *choice, level string) node {
+func (m *drawMemo) variantOf(s *drawstate.State, c *choice, level string) node {
 	n, drew := m.variant[level]
 	if !drew {
 		n = resolveChoice(s, c)

record.go

@@ -7,6 +7,8 @@ import (
 	"strings"
 	"unicode"
 	"unicode/utf8"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // Column is one rendered column of a record. Value is the rendered text, which a
@@ -133,7 +135,7 @@ func (f *Generator) FakeRecord(path string) (*Record, error) {
 	var frames frameStack
 	sc := renderScope{frames: &frames}
 	if t, isTable := n.(*table); isTable {
-		if n, sc.row, err = tableRecord(f.rand, t, tail); err != nil {
+		if n, sc.row, err = tableRecord(f.draws, t, tail); err != nil {
 			return nil, fmt.Errorf("fejkdata: %s: %w", path, err)
 		}
 	} else if len(tail) > 0 {
@@ -147,12 +149,12 @@ func (f *Generator) FakeRecord(path string) (*Record, error) {
 	if shape.err != nil {
 		return nil, fmt.Errorf("fejkdata: %s %w", path, shape.err)
 	}
-	return renderRecord(f.rand, shape.template, shape.columns, sc), nil
+	return renderRecord(f.draws, shape.template, shape.columns, sc), nil
 }
 
 // tableRecord walks a path's tail from a table to the table whose row is the record, and that
 // row, selected or drawn.
-func tableRecord(s *generatorState, t *table, tail []string) (node, renderedRow, error) {
+func tableRecord(s *drawstate.State, t *table, tail []string) (node, renderedRow, error) {
 	n, pins, err := descend(s, t, tail)
 	if err != nil {
 		return nil, renderedRow{}, err
@@ -204,7 +206,7 @@ func (t *RecordTemplate) Fake() *Record {
 	t.g.mu.Lock()
 	defer t.g.mu.Unlock()
 	var frames frameStack
-	return renderRecord(t.g.rand, t.template, t.columns, renderScope{frames: &frames})
+	return renderRecord(t.g.draws, t.template, t.columns, renderScope{frames: &frames})
 }
 
 // NewRecordTemplate compiles an inline record — a JSON object with a format and
@@ -260,7 +262,7 @@ func recordOf(n node) (*template, []Column, error) {
 
 // renderRecord draws each column once, in the name order recordOf fixed, as one render, so the
 // columns read one pick of each name; a table's columns read sc's row.
-func renderRecord(s *generatorState, t *template, columns []Column, sc renderScope) *Record {
+func renderRecord(s *drawstate.State, t *template, columns []Column, sc renderScope) *Record {
 	if mark := sc.renderFrame(t); mark >= 0 {
 		defer sc.frames.pop(mark)
 	}

render.go

@@ -3,10 +3,12 @@ package fejkdata
 import (
 	"fmt"
 	"strings"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // rng is the randomness a builtin sample draws from; *rand.Rand satisfies it. The
-// render path takes the concrete *generatorState instead, which keeps the draws of the walk
+// render path takes the concrete *drawstate.State instead, which keeps the draws of the walk
 // drawing through it off the heap.
 type rng interface {
 	IntN(n int) int
@@ -25,7 +27,7 @@ func (f *Generator) Fake(path string) (string, error) {
 		return "", fmt.Errorf("fejkdata: %w", err)
 	}
 	f.loadShippedAt(segments)
-	n, pins, err := descend(f.rand, &f.root, segments)
+	n, pins, err := descend(f.draws, &f.root, segments)
 	if err != nil {
 		return "", fmt.Errorf("fejkdata: %s: %w", path, err)
 	}
@@ -34,11 +36,11 @@ func (f *Generator) Fake(path string) (string, error) {
 	}
 	var frames frameStack
 	sc, _ := renderScope{frames: &frames}.at(n, &pins).enter(n, nil)
-	return render(f.rand, n, sc), nil
+	return render(f.draws, n, sc), nil
 }
 
 // descend walks a caller's path to the node it names, returning the rows its leaf renders in.
-func descend(s *generatorState, root node, segments []string) (node, pinSet, error) {
+func descend(s *drawstate.State, root node, segments []string) (node, pinSet, error) {
 	// docs/decisions.md#a-path-is-walked-once-without-drawing-before-it-is-walked-for-real
 	var buf [16]pathStep
 	steps, err := probePath(root, segments, buf[:0])
@@ -51,7 +53,7 @@ func descend(s *generatorState, root node, segments []string) (node, pinSet, err
 }
 
 // renderOnce renders n as one render, over frames of its own.
-func renderOnce(s *generatorState, n node) string {
+func renderOnce(s *drawstate.State, n node) string {
 	var frames frameStack
 	return render(s, n, renderScope{frames: &frames})
 }
@@ -59,7 +61,7 @@ func renderOnce(s *generatorState, n node) string {
 // render evaluates a compiled node to a string. compile validates every node up
 // front, so rendering a compiled tree cannot fail.
 // A child this switch renders is one renderEdges must list too, or the fences miss it.
-func render(s *generatorState, n node, sc renderScope) string {
+func render(s *drawstate.State, n node, sc renderScope) string {
 	switch n := n.(type) {
 	case *choice:
 		return render(s, pick(s, n), sc)
@@ -94,7 +96,7 @@ func render(s *generatorState, n node, sc renderScope) string {
 
 // renderRepeat renders each iteration of t inside the name scopes rendering t, where a name bound
 // outside t keeps its pick, and a name t binds picks again.
-func renderRepeat(s *generatorState, t *template, sc renderScope) string {
+func renderRepeat(s *drawstate.State, t *template, sc renderScope) string {
 	var b strings.Builder
 	b.Grow(t.repeat * (t.compiled.grow + len(t.separator)))
 	for i := 0; i < t.repeat; i++ {
@@ -114,14 +116,14 @@ func renderRepeat(s *generatorState, t *template, sc renderScope) string {
 
 // pick selects one item. Uniform choices are O(1); weighted choices are an
 // O(log n) search over precomputed cumulative weights.
-func pick(s *generatorState, c *choice) node {
+func pick(s *drawstate.State, c *choice) node {
 	if c.cum == nil {
 		return c.items[s.IntN(len(c.items))]
 	}
 	return c.items[pickCum(s, c.cum)]
 }
 
-func expand(s *generatorState, t *template, sc renderScope) string {
+func expand(s *drawstate.State, t *template, sc renderScope) string {
 	var b strings.Builder
 	b.Grow(t.compiled.grow)
 	for i := range t.compiled.ops {
@@ -148,7 +150,7 @@ func expand(s *generatorState, t *template, sc renderScope) string {
 // readField renders one arm of a token. A read of a name, or of a level a read of the name
 // rendering addresses, is kept in that name's pick; every other read draws afresh, so {word}
 // {word} draws twice and {p.a} {p.b} reads two draws of p.
-func readField(s *generatorState, t *template, sc renderScope, a arm) readValue {
+func readField(s *drawstate.State, t *template, sc renderScope, a arm) readValue {
 	switch {
 	case a.kind == namedRead:
 		return readName(s, sc, a)
@@ -170,7 +172,7 @@ func readField(s *generatorState, t *template, sc renderScope, a arm) readValue
 
 // renderLeaf draws and renders what a read lands on: null on a null item, or on a column that only
 // reads one reference or name whose read drew null.
-func renderLeaf(s *generatorState, n node, sc renderScope) readValue {
+func renderLeaf(s *drawstate.State, n node, sc renderScope) readValue {
 	n = resolveChoice(s, n)
 	switch leaf := n.(type) {
 	case *nullItem:
@@ -185,7 +187,7 @@ func renderLeaf(s *generatorState, n node, sc renderScope) readValue {
 
 // resolveChoice resolves a choice to one variant. Nested choices unwrap too: a draw is one value,
 // not another set to pick from.
-func resolveChoice(s *generatorState, n node) node {
+func resolveChoice(s *drawstate.State, n node) node {
 	for c, ok := n.(*choice); ok; c, ok = n.(*choice) {
 		n = pick(s, c)
 	}

struct.go

@@ -8,6 +8,8 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // FakeStruct fills the struct v points to. Each exported field tagged `fake:"…"` is a
@@ -27,7 +29,7 @@ func (f *Generator) FakeStruct(v any) error {
 	if err != nil {
 		return fmt.Errorf("fejkdata: %w", err)
 	}
-	shape.fill(f.rand, p.Elem())
+	shape.fill(f.draws, p.Elem())
 	return nil
 }
 
@@ -316,7 +318,7 @@ func (k columnKind) holds(v proven) bool {
 }
 
 // fill draws the record into v's tagged fields, then each nested struct as a record of its own.
-func (s *structShape) fill(state *generatorState, v reflect.Value) {
+func (s *structShape) fill(state *drawstate.State, v reflect.Value) {
 	if s.record != nil {
 		var frames frameStack
 		for i, c := range renderRecord(state, s.record, s.columns, renderScope{frames: &frames}).columns {

table.go

@@ -7,6 +7,8 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // table is a category whose rows come from a TSV beside it: the header names the
@@ -470,20 +472,20 @@ func (t *table) builtLookup() *rowLookup {
 	return &t.lookup
 }
 
-func (t *table) drawRow(s *generatorState) int {
+func (t *table) drawRow(s *drawstate.State) int {
 	if t.cum == nil {
 		return s.IntN(t.rowCount())
 	}
 	return pickCum(s, t.cum)
 }
 
-func pickCum(s *generatorState, cum []float64) int {
+func pickCum(s *drawstate.State, cum []float64) int {
 	x := s.Float64() * cum[len(cum)-1]
 	return min(sort.Search(len(cum), func(i int) bool { return cum[i] > x }), len(cum)-1) // x can round up to the total
 }
 
 // drawUnder picks a row among those linked to parent row pr.
-func (t *table) drawUnder(s *generatorState, pr int) int {
+func (t *table) drawUnder(s *drawstate.State, pr int) int {
 	lookup := t.builtLookup()
 	k := t.parentT.cell(pr, t.parentT.keyIndex)
 	rows := lookup.rowsByParent[k]
@@ -496,7 +498,7 @@ func (t *table) drawUnder(s *generatorState, pr int) int {
 // drawIn is the row of t a path or a named pick reads: the one pinned in p, else one drawn inside the nearest
 // pinned ancestor — its parent drawn inside that first where the ancestor is further up — or
 // over the whole table, and pinned with its ancestors.
-func (t *table) drawIn(s *generatorState, p *pinSet) int {
+func (t *table) drawIn(s *drawstate.State, p *pinSet) int {
 	if r, ok := p.pinned(t); ok {
 		return r
 	}

transform.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"strings"
 	"unicode"
+
+	"github.com/larvit/fejkdata/internal/drawstate"
 )
 
 // transforms are the builtins that rewrite one operand's value; they nest, so
@@ -65,7 +67,7 @@ func transformPrep(outer func(string) string) func([]string) callFn {
 		if err != nil {
 			panic(internalError("transform arg %q reached prep unvalidated: %v", a[0], err))
 		}
-		return func(_ *generatorState, _ string, operands []string) string {
+		return func(_ *drawstate.State, _ string, operands []string) string {
 			v := operands[0]
 			for i := len(chain) - 1; i >= 0; i-- {
 				v = chain[i](v)