Give maxLen its own literal and repeats MaxRepeat; arg errors name the spelling and the range; write's comment says what Flush reports; assert 64-bit at compile time

README.md

@@ -247,7 +247,8 @@ hyphenated field can't be an operand.
 Renders e.g. `19.99 x 3 = 59.97`. An operand that can never be a number (`"abc"`,
 or a choice of such) is rejected at load, as is a division by a constant zero
 (`1/0`, or a fixed `"0"` field); an operand that sometimes is not a number yields
-`NaN`, and a division by a sometimes-zero one `Inf` — both print rather than fail.
+`NaN`, and a division by one that is not constant `Inf` — both print rather than
+fail.
 
 ### Transforms
 
@@ -390,14 +391,16 @@ tokens add cost in proportion to the output.
 - **64-bit targets only.** The gate builds amd64, and the buffer sizing a render
   pre-computes (renders × bytes) assumes a 64-bit int; on a 32-bit target it could
   overflow and panic.
-- **A constant zero divisor is a load error; a sometimes-zero one prints `Inf`.**
-  `1/0` and a fixed `"0"` field are decidable, so they join the never-numeric
-  operand as a load error; a divisor that is only sometimes zero is data, and
-  `Inf` printing visibly is the never-fail rule.
-- **A default written out, and a constant spelled as a sample, are load errors.**
-  `weight: 1`, `repeat: 1`, `separator: ""`, `int(5,5)`, `float(1,1,2)`, `+5`
-  and `05` each spell what a shorter form already spells, so each is rejected
-  naming that form.
+- **A constant zero divisor is a load error; a divisor that is not constant prints
+  `Inf`.** `1/0` and a fixed `"0"` field are decidable, so they join the
+  never-numeric operand as a load error; the fold stops where an operand varies,
+  so `a/(b*c)` with `b` fixed at `0` and `c` varying loads and prints `Inf` every
+  draw — catching it needs zero-absorbing algebra for a shape nobody writes.
+- **In data, a default written out and a constant spelled as a sample are load
+  errors.** `weight: 1`, `repeat: 1`, `separator: ""`, `int(5,5)`, `float(1,1,2)`,
+  `+5` and `05` each spell what a shorter form already spells, so each is rejected
+  naming that form. The CLI's numbers follow the shell instead: `--seed 007` and
+  `--repeat +3` are 7 and 3, as every command line reads them.
 - **Samples say what they emit, transforms what they do.** `{upper(2)}` is two
   letters, `{uppercase(x)}` is `x` upper-cased; one name for both would turn on
   whether the argument looks like a number.

builtins.go

@@ -2,6 +2,7 @@ package fejkdata
 
 import (
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"math"
 	"strconv"
@@ -9,12 +10,12 @@ import (
 	"unicode"
 )
 
-// maxLen caps sample output lengths (hex, nanoid, base64) and the renders a repeat
-// multiplies to along any path; maxDecimals caps float/calc decimal places. So a
-// fat-fingered or overflowing argument fails at New instead of trying to allocate
-// gigabytes — or panicking — at render.
+// maxLen caps sample output lengths (hex, nanoid, base64, digits, upper, lower)
+// and maxDecimals float/calc decimal places, so a fat-fingered or overflowing
+// argument fails at New instead of trying to allocate gigabytes — or panicking —
+// at render.
 const (
-	maxLen      = MaxRepeat
+	maxLen      = 1 << 20
 	maxDecimals = 1024
 )
 
@@ -224,6 +225,9 @@ func randChars(r rng, n int, alphabet string) string {
 // plainInt parses an integer arg written the one way: no sign, no leading zero.
 func plainInt(s string) (int, error) {
 	n, err := strconv.Atoi(s)
+	if errors.Is(err, strconv.ErrRange) {
+		return 0, fmt.Errorf("%q is past the integer range: %w", s, err)
+	}
 	if err != nil {
 		return 0, fmt.Errorf("%q is not an integer", s)
 	}
@@ -235,6 +239,9 @@ func plainInt(s string) (int, error) {
 
 func posIntArg(_ map[string]node, a []string) error {
 	n, err := plainInt(a[0])
+	if errors.Is(err, strconv.ErrRange) {
+		return fmt.Errorf("count %q exceeds the maximum %d", a[0], maxLen)
+	}
 	if err != nil {
 		return fmt.Errorf("count %w", err)
 	}
@@ -248,10 +255,13 @@ func posIntArg(_ map[string]node, a []string) error {
 }
 
 func intRangeArgs(_ map[string]node, a []string) error {
-	lo, e1 := plainInt(a[0])
-	hi, e2 := plainInt(a[1])
-	if e1 != nil || e2 != nil {
-		return fmt.Errorf("int(min,max) needs plain integers, got %q,%q", a[0], a[1])
+	lo, err := plainInt(a[0])
+	if err != nil {
+		return fmt.Errorf("int(min,max): min %w", err)
+	}
+	hi, err := plainInt(a[1])
+	if err != nil {
+		return fmt.Errorf("int(min,max): max %w", err)
 	}
 	if lo > hi {
 		return fmt.Errorf("int(min,max): min %d > max %d", lo, hi)
@@ -268,9 +278,12 @@ func intRangeArgs(_ map[string]node, a []string) error {
 func floatArgs(_ map[string]node, a []string) error {
 	lo, e1 := strconv.ParseFloat(a[0], 64)
 	hi, e2 := strconv.ParseFloat(a[1], 64)
-	dp, e3 := plainInt(a[2])
-	if e1 != nil || e2 != nil || e3 != nil {
-		return fmt.Errorf("float(min,max,dp) needs numeric bounds and a plain decimals count, got %q,%q,%q", a[0], a[1], a[2])
+	if e1 != nil || e2 != nil {
+		return fmt.Errorf("float(min,max,dp) needs numeric bounds, got %q,%q", a[0], a[1])
+	}
+	dp, err := plainInt(a[2])
+	if err != nil {
+		return fmt.Errorf("float(min,max,dp): decimals %w", err)
 	}
 	if math.IsNaN(lo) || math.IsNaN(hi) || math.IsInf(lo, 0) || math.IsInf(hi, 0) {
 		return fmt.Errorf("float(min,max,dp) needs finite bounds, got %q,%q", a[0], a[1])

calc.go

@@ -82,8 +82,12 @@ func checkCalc(fields map[string]node, args []string) error {
 		return fmt.Errorf("calc(%q) divides by %s, which is always zero", args[0], divisor)
 	}
 	if len(args) == 2 {
-		if dp, err := plainInt(args[1]); err != nil || dp < 0 || dp > maxDecimals {
-			return fmt.Errorf("calc decimals %q must be a plain integer in 0..%d", args[1], maxDecimals)
+		dp, err := plainInt(args[1])
+		if err != nil {
+			return fmt.Errorf("calc decimals %w", err)
+		}
+		if dp < 0 || dp > maxDecimals {
+			return fmt.Errorf("calc decimals %d must be in 0..%d", dp, maxDecimals)
 		}
 	}
 	return nil

cmd/fejkdata/main.go

@@ -215,8 +215,9 @@ func (in invocation) options() []fejkdata.Option {
 }
 
 // write streams the path's renders to w, repeat of them joined by the separator
-// and ended by a newline. A path that renders once renders every time, so the only
-// failure comes before anything is written.
+// and ended by a newline. A path that renders once renders every time, so a Fake
+// failure comes before anything is written; a write failure surfaces from Flush,
+// bufio keeping the first one.
 func (in invocation) write(f *fejkdata.Generator, w io.Writer) error {
 	out := bufio.NewWriter(w)
 	for i := 0; i < in.repeat; i++ {

fejkdata.go

@@ -28,9 +28,12 @@ import (
 //go:embed data
 var shippedFS embed.FS
 
-// MaxRepeat caps a repeat, and the renders nested repeats multiply to along any path.
+// MaxRepeat caps a repeat, and the renders nested repeats multiply to along any
+// path; the CLI's --repeat shares it.
 const MaxRepeat = 1 << 20
 
+var _ [^uint(0)>>63 - 1]struct{} // 64-bit only, per the README's Decisions
+
 // ErrNoData is returned by New when no source is loaded at all.
 var ErrNoData = errors.New("no data: WithoutShippedData needs at least one WithDataPath or WithDataFS")
 
@@ -207,7 +210,7 @@ func join(prefix, name string) string {
 	return prefix + "." + name
 }
 
-// randomBytes seeds an unseeded generator; a failure is an error, never a fixed seed.
+// randomBytes seeds an unseeded generator.
 var randomBytes = crand.Read
 
 func newRand(seed uint64, seeded bool) (*session, error) {

graph.go

@@ -181,8 +181,8 @@ func checkRepeatReach(root map[string]node) error {
 		return r
 	}
 	return walkNodes(root, func(path string, n node) error {
-		if t, ok := n.(*template); ok && t.repeat > 1 && of(n) > maxLen {
-			return fmt.Errorf("%s: repeat %d multiplies to %d renders along one path, above the maximum %d", path, t.repeat, of(n), maxLen)
+		if t, ok := n.(*template); ok && t.repeat > 1 && of(n) > MaxRepeat {
+			return fmt.Errorf("%s: repeat %d multiplies to %d renders along one path, above the maximum %d", path, t.repeat, of(n), MaxRepeat)
 		}
 		return nil
 	})

node.go

@@ -288,8 +288,8 @@ func repeatOf(m map[string]any) (int, error) {
 	if r == 1 {
 		return 0, fmt.Errorf("repeat 1 is the default, so it has no effect; drop it")
 	}
-	if r > maxLen { // caps the renders one repeat asks for; checkRepeatReach bounds what nested ones multiply to
-		return 0, fmt.Errorf("repeat %v exceeds the maximum %d", rv, maxLen)
+	if r > MaxRepeat { // caps the renders one repeat asks for; checkRepeatReach bounds what nested ones multiply to
+		return 0, fmt.Errorf("repeat %v exceeds the maximum %d", rv, MaxRepeat)
 	}
 	return int(r), nil
 }