east

name

east

description

East programming language - a statically typed, expression-based language embedded in TypeScript. Use when writing East programs with @elaraai/east. Triggers for: (1) Writing East functions with East.function() or East.asyncFunction(), (2) Defining types (IntegerType, StringType, ArrayType, StructType, VariantType, etc.), (3) Using platform functions with East.platform() or East.asyncPlatform(), (4) Compiling East programs with East.compile(), (5) Working with East expressions (arithmetic, collections, control flow), (6) Serializing East IR with .toIR() and EastIR.fromJSON(), (7) Standard library operations (formatting, rounding, generation).

East Language

A statically typed, expression-based programming language embedded in TypeScript. Write programs using a fluent API, compile to portable IR.

Quick Start

// Types and helpers are direct imports (NOT East.IntegerType)
import { East, IntegerType, StringType, ArrayType, NullType } from "@elaraai/east";

// 1. Define platform functions (East.platform)
const log = East.platform("log", [StringType], NullType);
const platform = [log.implement(console.log)];

// 2. Define East function (East.function)
const sumArray = East.function([ArrayType(IntegerType)], IntegerType, ($, arr) => {
    const total = $.let(arr.sum());
    $(log(East.str`Sum: ${total}`));
    $.return(total);
});

// 3. Compile and execute (East.compile)
const compiled = East.compile(sumArray, platform);
compiled([1n, 2n, 3n]);  // logs "Sum: 6", returns 6n

Decision Tree: What Do You Need?

Task → What do you need?
    │
    ├─ Create East Expressions (East.*)
    │   ├─ From TypeScript value → East.value(tsValue) or East.value(tsValue, Type)
    │   ├─ String interpolation → East.str`Hello ${name}!`
    │   └─ Inside function body → $.let(value), $.const(value)
    │
    ├─ Define a Type (import from package, NOT East.*)
    │   ├─ Primitive → IntegerType, FloatType, StringType, BooleanType, DateTimeType, BlobType, NullType
    │   ├─ Collection → ArrayType(T), SetType(K), DictType(K, V), RefType(T)
    │   ├─ Numeric → VectorType(T), MatrixType(T) where T is FloatType, IntegerType, or BooleanType
    │   ├─ Compound → StructType({...}), VariantType({...}), RecursiveType(...)
    │   ├─ Function → FunctionType<I, O>, AsyncFunctionType<I, O>
    │   └─ Patch → PatchType(T) (compute patch type for any East type)
    │
    ├─ Create TypeScript Values for East Types
    │   ├─ NullType → null
    │   ├─ BooleanType → true, false
    │   ├─ IntegerType → 42n (bigint literal)
    │   ├─ FloatType → 3.14 (number literal)
    │   ├─ StringType → "hello"
    │   ├─ DateTimeType → new Date("2025-01-01T00:00:00Z")
    │   ├─ BlobType → new Uint8Array([...])
    │   ├─ ArrayType(T) → [1n, 2n, 3n]
    │   ├─ SetType(K) → new Set([1n, 2n, 3n])
    │   ├─ DictType(K, V) → new Map([["a", 1n], ["b", 2n]])
    │   ├─ StructType({...}) → { field1: value1, field2: value2 }
    │   ├─ VariantType({...}) (use helpers from package)
    │   │   ├─ Option type → some(value), none  ← preferred for Option/Maybe
    │   │   └─ Other variants → variant("caseName", value)
    │   ├─ VectorType(FloatType) → new Float64Array([1.0, 2.0, 3.0])
    │   ├─ VectorType(IntegerType) → new BigInt64Array([1n, 2n, 3n])
    │   ├─ VectorType(BooleanType) → new Uint8ClampedArray([1, 0, 1])
    │   ├─ MatrixType(FloatType) → matrix(Float64Array.from([1.0, 2.0, 3.0, 4.0]), 2, 2)
    │   ├─ MatrixType(IntegerType) → matrix(BigInt64Array.from([1n, 2n, 3n, 4n]), 2, 2)
    │   ├─ MatrixType(BooleanType) → matrix(Uint8ClampedArray.from([1, 0, 0, 1]), 2, 2)
    │   └─ RefType(T) (use helper from package) → ref(value)
    │
    ├─ Write a Function (East.*)
    │   ├─ Synchronous → East.function([inputs], output, ($, ...args) => { ... })
    │   └─ Asynchronous → East.asyncFunction([inputs], output, ($, ...args) => { ... })
    │
    ├─ Compile and Execute (East.*)
    │   ├─ Sync function → East.compile(fn, platform)
    │   └─ Async function → East.compileAsync(fn, platform)
    │
    ├─ Use Platform Effects (East.*)
    │   ├─ Sync effect → East.platform("name", [inputs], output).implement(fn)
    │   └─ Async effect → East.asyncPlatform("name", [inputs], output).implement(fn)
    │
    ├─ Block Operations ($)
    │   ├─ Variables → $.let(value), $.const(value), $.assign(var, value)
    │   ├─ Execute → $(expr), $.return(value), $.error(message)
    │   ├─ Control Flow → $.if(...), $.while(...), $.for(...), $.match(...), $.matchTag(...)
    │   └─ Error Handling → $.try(...).catch(...).finally(...)
    │
    ├─ Expression Operations
    │   ├─ Boolean
    │   │   ├─ Logic → .and($=>), .or($=>), .not(), .ifElse($=>,$=>)
    │   │   ├─ Bitwise → .bitAnd(), .bitOr(), .bitXor()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   ├─ Integer
    │   │   ├─ Math → .add()/.plus(), .subtract()/.sub()/.minus(), .multiply()/.mul()/.times(), .divide()/.div(), .remainder()/.mod()/.rem()/.modulo(), .pow(), .abs(), .sign(), .negate(), .log()
    │   │   ├─ Convert → .toFloat()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne(), .lessThan()/.less()/.lt(), .greaterThan()/.greater()/.gt(), .lessThanOrEqual()/.lessEqual()/.lte()/.le(), .greaterThanOrEqual()/.greaterEqual()/.gte()/.ge()
    │   ├─ Float
    │   │   ├─ Math → .add()/.plus(), .subtract()/.sub()/.minus(), .multiply()/.mul()/.times(), .divide()/.div(), .remainder()/.mod()/.rem()/.modulo(), .pow(), .abs(), .sign(), .negate()
    │   │   ├─ Advanced → .sqrt(), .exp(), .log(), .sin(), .cos(), .tan()
    │   │   ├─ Convert → .toInteger()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne(), .lessThan()/.less()/.lt(), .greaterThan()/.greater()/.gt(), .lessThanOrEqual()/.lessEqual()/.lte()/.le(), .greaterThanOrEqual()/.greaterEqual()/.gte()/.ge()
    │   ├─ String
    │   │   ├─ Transform → .concat(), .repeat(), .substring(), .upperCase(), .lowerCase(), .trim(), .trimStart(), .trimEnd()
    │   │   ├─ Replace → .replace(), .replaceAll(), .split()
    │   │   ├─ Query → .length(), .startsWith(), .endsWith(), .contains(), .indexOf(), .charAt()
    │   │   ├─ Parse → .parse(), .parseJson()
    │   │   ├─ Encode → .encodeUtf8(), .encodeUtf16()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne(), .lessThan()/.less()/.lt(), .greaterThan()/.greater()/.gt(), .lessThanOrEqual()/.lessEqual()/.lte()/.le(), .greaterThanOrEqual()/.greaterEqual()/.gte()/.ge()
    │   ├─ DateTime
    │   │   ├─ Components → .getYear(), .getMonth(), .getDayOfMonth(), .getDayOfWeek(), .getHour(), .getMinute(), .getSecond(), .getMillisecond()
    │   │   ├─ Arithmetic → .addDays(), .subtractDays(), .addHours(), .subtractHours(), .addMinutes(), .addSeconds(), .addMilliseconds(), .addWeeks()
    │   │   ├─ Duration → .durationDays(), .durationHours(), .durationMinutes(), .durationSeconds(), .durationMilliseconds(), .durationWeeks()
    │   │   ├─ Convert → .toEpochMilliseconds(), .printFormatted()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne(), .lessThan()/.less()/.lt(), .greaterThan()/.greater()/.gt(), .lessThanOrEqual()/.lessEqual()/.lte()/.le(), .greaterThanOrEqual()/.greaterEqual()/.gte()/.ge()
    │   ├─ Blob
    │   │   ├─ Read → .size(), .getUint8()
    │   │   ├─ Decode → .decodeUtf8(), .decodeUtf16(), .decodeBeast(), .decodeCsv(rowType, { nullStrings: [] by default (empty field == empty string; opt in for none), defaults: per-column fallback/constant-fill, trimFields, … })
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   ├─ Array
    │   │   ├─ Read → .size(), .length(), .has(), .get(), .at(), .tryGet(), .getKeys()
    │   │   ├─ Mutate → .update(), .pushLast(), .popLast(), .pushFirst(), .popFirst(), .append(), .prepend(), .clear(), .sortInPlace(), .reverseInPlace()
    │   │   ├─ Transform → .copy(), .slice(), .concat(), .sort(), .reverse(), .map(), .filter(), .filterMap(), .flatMap()
    │   │   ├─ Search → .findFirst(), .findAll(), .firstMap(), .isSorted()
    │   │   ├─ Reduce → .reduce(), .every(), .some(), .sum(), .mean(), .maximum(), .minimum(), .findMaximum(), .findMinimum()
    │   │   ├─ Convert → .stringJoin(), .toSet(), .toDict(), .flattenToSet(), .flattenToDict(), .encodeCsv()
    │   │   ├─ Group → .groupReduce(), .groupSize(), .groupSum(), .groupMean(), .groupMinimum(), .groupMaximum(), .groupToArrays(), .groupToSets(), .groupToDicts(), .groupEvery(), .groupSome()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   ├─ Set
    │   │   ├─ Read → .size(), .has()
    │   │   ├─ Mutate → .insert(), .tryInsert(), .delete(), .tryDelete(), .clear(), .unionInPlace()
    │   │   ├─ Set Ops → .copy(), .union(), .intersection(), .difference(), .symmetricDifference(), .isSubsetOf(), .isSupersetOf(), .isDisjointFrom()
    │   │   ├─ Transform → .filter(), .filterMap(), .map(), .forEach(), .firstMap()
    │   │   ├─ Reduce → .reduce(), .every(), .some(), .sum(), .mean()
    │   │   ├─ Convert → .toArray(), .toSet(), .toDict(), .flattenToArray(), .flattenToSet(), .flattenToDict()
    │   │   ├─ Group → .groupReduce(), .groupSize(), .groupSum(), .groupMean(), .groupToArrays(), .groupToSets(), .groupToDicts(), .groupEvery(), .groupSome()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   ├─ Dict
    │   │   ├─ Read → .size(), .has(), .get(), .tryGet(), .keys(), .getKeys()
    │   │   ├─ Mutate → .insert(), .insertOrUpdate(), .update(), .merge(), .getOrInsert(), .delete(), .tryDelete(), .pop(), .swap(), .clear(), .unionInPlace()
    │   │   ├─ Transform → .copy(), .map(), .filter(), .filterMap(), .forEach(), .firstMap()
    │   │   ├─ Reduce → .reduce(), .every(), .some(), .sum(), .mean()
    │   │   ├─ Convert → .toArray(), .toSet(), .toDict(), .flattenToArray(), .flattenToSet(), .flattenToDict()
    │   │   ├─ Group → .groupReduce(), .groupSize(), .groupSum(), .groupMean(), .groupToArrays(), .groupToSets(), .groupToDicts(), .groupEvery(), .groupSome()
    │   │   └─ Compare → .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   ├─ Vector
    │   │   ├─ Read → .length(), .get()
    │   │   ├─ Functional update → .set() (returns a new vector)
    │   │   ├─ Transform → .slice(), .concat(), .map(), .reduce()
    │   │   └─ Convert → .toArray(), .toMatrix()
    │   ├─ Matrix
    │   │   ├─ Read → .rows(), .cols(), .get(), .getRow(), .getCol()
    │   │   ├─ Functional update → .set() (returns a new matrix)
    │   │   ├─ Transform → .transpose()
    │   │   └─ Convert → .toVector(), .toArray()
    │   ├─ Struct → .fieldName (direct property access)
    │   ├─ Variant → .match(), .matchTag(), .unwrap(), .hasTag(), .getTag(), .equals()/.equal()/.eq(), .notEquals()/.notEqual()/.ne()
    │   └─ Ref → .get(), .update(), .merge()
    │
    ├─ Standard Library (East.*)
    │   ├─ Integer → East.Integer.printCommaSeperated(), .roundNearest(), .printOrdinal()
    │   ├─ Float → East.Float.roundToDecimals(), .printCurrency(), .printCompact()
    │   ├─ DateTime → East.DateTime.fromComponents(), .roundDownDay(), .parseFormatted()
    │   ├─ Array → East.Array.range(), .linspace(), .generate()
    │   ├─ Set → East.Set.generate()
    │   ├─ Dict → East.Dict.generate()
    │   ├─ Blob → East.Blob.encodeBeast(), blob.decodeCsv(), array.encodeCsv()
    │   ├─ Vector → East.Vector.zeros(), .ones(), .fill(), .fromArray()
    │   ├─ Matrix → East.Matrix.zeros(), .ones(), .fill(), .fromArray()
    │   └─ String → East.String.printJson(), East.String.printError()
    │
    ├─ Comparisons (East.*)
    │   ├─ Equality → East.equal()/.equals()/.eq(), East.notEqual()/.notEquals()/.ne()
    │   ├─ Ordering → East.less()/.lessThan()/.lt(), East.greater()/.greaterThan()/.gt()
    │   ├─ Bounds → East.lessEqual()/.lte()/.le(), East.greaterEqual()/.gte()/.ge()
    │   ├─ Identity → East.is() (identity equality; use East.equal() for value equality)
    │   └─ Utilities → East.min(), East.max(), East.clamp()
    │
    ├─ Conversion (East.*)
    │   └─ To string → East.print(expr)
    │
    ├─ Patch Operations (East.*)
    │   ├─ Compute diff → East.diff(before, after) → returns patch
    │   ├─ Apply patch → East.applyPatch(value, patch) → returns patched value
    │   ├─ Compose patches → East.composePatch(first, second, type) → returns combined patch
    │   └─ Invert patch → East.invertPatch(patch, type) → returns undo patch
    │
    └─ Serialization
        ├─ IR → fn.toIR(), ir.toJSON(), EastIR.fromJSON(data).compile(platform)
        ├─ Data, INSIDE an East function → East.Blob.encodeBeast(value, 'v2'), blob.decodeBeast(type, 'v2')
        └─ Data, from TypeScript (host side, `@elaraai/east`) — see "Binary serialization (beast2)"
            ├─ Whole value → encodeBeast2For(T)(value) / decodeBeast2For(T)(blob)
            │   └─ Don't know the type? → decodeBeast2(blob) → { type, value }
            ├─ Collection too big for memory
            │   ├─ Write → new Beast2Writer(T, sink); w.write(batch); w.finish()  — memory is ONE batch
            │   │   └─ already in memory → encodeBeast2SegmentsFor(T)(batches)
            │   ├─ Read a batch at a time → iterBeast2SegmentsFor(T)(blob)   — O(segment)
            │   └─ Read whole (batches merge) → decodeBeast2For(T)(blob)
            ├─ Random access by row → openBeast2PagesFor(T)(blob) → .elementCount, .segment(i), .element(row)
            └─ In a browser (no node:zlib) → decodeBeast2ForAsync(T)(blob)

Type System Summary

Type	ValueTypeOf<Type>	Mutability
NullType	null	Immutable
BooleanType	boolean	Immutable
IntegerType	bigint	Immutable
FloatType	number	Immutable
StringType	string	Immutable
DateTimeType	Date	Immutable
BlobType	Uint8Array	Immutable
ArrayType<T>	ValueTypeOf<T>[]	Mutable
SetType<K>	Set<ValueTypeOf<K>>	Mutable
DictType<K, V>	Map<ValueTypeOf<K>, ValueTypeOf<V>>	Mutable
RefType<T>	ref<ValueTypeOf<T>>	Mutable
VectorType<FloatType>	Float64Array	Immutable
VectorType<IntegerType>	BigInt64Array	Immutable
VectorType<BooleanType>	Uint8ClampedArray	Immutable
MatrixType<T>	matrix<TypedArray>	Immutable
StructType<Fields>	{...}	Immutable
VariantType<Cases>	variant	Immutable
FunctionType<I, O>	Function	Immutable
PatchType<T>	variant	Immutable

Key Patterns

TypeScript Values vs East Expressions

TypeScript values and East expressions are different. East methods only work on East expressions.

// WRONG - Cannot call East methods on TypeScript values
const THRESHOLD = 100n;  // This is a TypeScript bigint
East.function([IntegerType], BooleanType, ($, x) => {
    $.return(x.greaterThan(THRESHOLD));  // ERROR: THRESHOLD has no .greaterThan()
});

// CORRECT - Wrap TypeScript values with East.value()
const THRESHOLD = 100n;
East.function([IntegerType], BooleanType, ($, x) => {
    $.return(x.greaterThan(East.value(THRESHOLD)));  // OK
});

// ALSO CORRECT - Use $.const() inside the function
East.function([IntegerType], BooleanType, ($, x) => {
    const threshold = $.const(THRESHOLD);  // Creates East expression
    $.return(x.greaterThan(threshold));    // OK
});

Rule: Function parameters are already East expressions. External TypeScript values must be wrapped with East.value() or bound with $.const().

Creating Variant Values

import { variant, some, none, ref } from "@elaraai/east";

// Option types - use some() and none helpers (preferred)
const hasValue = some(42n);      // { type: "some", value: 42n }
const noValue = none;            // { type: "none", value: null }

// AVOID: variant("some", ...) and variant("none", ...) for Option types
// const hasValue = variant("some", 42n);  // works but use some() instead
// const noValue = variant("none", null);  // works but use none instead

// Other variant types - use variant()
const success = variant("ok", "done");
const failure = variant("error", "failed");

// Mutable references - use ref()
const counter = ref(0n);

String Interpolation

// East.str`` creates a StringExpr from a template
// Only East expressions can be interpolated, NOT plain TypeScript values

const MY_CONSTANT = 100n;  // TypeScript value

East.function([IntegerType], StringType, ($, x) => {
    // CORRECT - x is already an East expression (function parameter)
    const msg1 = $.let(East.str`Value: ${x}`);

    // CORRECT - wrap TypeScript constant with East.value()
    const msg2 = $.let(East.str`Threshold: ${East.value(MY_CONSTANT)}`);

    // CORRECT - use $.const() to create East expression first
    const threshold = $.const(MY_CONSTANT);
    const msg3 = $.let(East.str`Threshold: ${threshold}`);

    // WRONG - cannot interpolate plain TypeScript values
    // const msg4 = $.let(East.str`Threshold: ${MY_CONSTANT}`);  // ERROR

    $.return(msg1);
});

Error Handling

$.try($ => {
    $.assign(result, arr.get(index));
}).catch(($, message, stack) => {
    $.assign(result, -1n);
}).finally($ => {
    // cleanup
});

Platform Function Implementations

// Platform implementations are raw TypeScript functions that receive/return the
// `ValueTypeOf<Type>` for each East type — see the Type System Summary table
// above (Integer→bigint, Float→number, String→string, Boolean→boolean,
// DateTime→Date, Blob→Uint8Array, Struct→plain object, Array→array, Dict→Map,
// Set→Set, Variant→variant()). Build them with `variant()`/`some`/`none` etc.

// Sync platform - regular TypeScript function
const log = East.platform("log", [StringType], NullType);
const timeNs = East.platform("time_ns", [], IntegerType);

// Async platform - async TypeScript function
const fetchStatus = East.asyncPlatform("fetch_status", [StringType], StringType);

// Implementations receive/return TypeScript values matching East types
const platform = [
    log.implement(console.log),                          // (msg: string) => void
    timeNs.implement(() => process.hrtime.bigint()),     // () => bigint
    fetchStatus.implement(async (url: string) => {       // async function OK
        const response = await fetch(url);
        return `${response.status}`;
    }),
];

// In East code: NO await needed - async is handled automatically
const myFn = East.asyncFunction([StringType], NullType, ($, url) => {
    const t1 = $.let(timeNs());
    const status = $.let(fetchStatus(url));  // no await, just call it
    const t2 = $.let(timeNs());
    $(log(East.str`Fetched in ${t2.subtract(t1)} ns, status: ${status}`));
});

// Compile async functions with East.compileAsync
const compiled = East.compileAsync(myFn, platform);
await compiled("https://example.com");  // await at the outer TypeScript level

// `{ optional: true }` lets a function compile with NO implementation (it throws
// at runtime if called unimplemented) — useful for declaring an interface:
const maybe = East.platform("maybe", [StringType], StringType, { optional: true });

Project-owned platform functions (calling your own code from e3)

The East.compile(fn, platform) flow above is the in-process path. To call a platform function from an e3 task instead, you don't call compile — you default-export the PlatformFunction[] as your package's ./platform subpath, and the e3 runner loads it. Two rules then apply:

• Name it dotted "<project>.<fn>", and the name in the East.platform(...) declaration must byte-match the implementation (and the Python impl, if you also implement it there).
• The e3 task references it via { runtime: "east-node", platforms: [{ custom: "@elaraai/<project>" }] } (the package's own scoped name).

See east-project for the full wiring (the ./platform export, the --platform scaffold) and e3 for the task runner; east-py for the Python sibling (@platform_function).

Binary serialization (beast2)

East.Blob.encodeBeast(value, 'v2') is the builtin you call inside an East function. The functions below are the host-side TypeScript API for the same format — you call them from ordinary TypeScript, not from an East body.

Blobs are self-describing and the container version is sniffed on read, so a decoder built for a type reads any version that type was written in. There is no call-site change to adopt a newer container.

Signature	Description
Whole value
encodeBeast2For(T, opts?): (value) => Uint8Array	Curried encoder. opts.version picks the container (4 default, 5); opts.codec ("deflate" default | "none") and opts.index apply to v5
decodeBeast2For(T, opts?): (blob) => ValueTypeOf<T>	Curried decoder; accepts any container version. opts.platform supplies platform fns for decoded East functions
decodeBeast2(blob, opts?): { type, value }	Decode without knowing the type — reads the type embedded in the blob
decodeBeast2ForAsync(T, opts?): (blob) => Promise<…>	Same as decodeBeast2For, but decompresses via DecompressionStream — use in browsers, where node:zlib is unavailable
encodeEastIR(eastIR) / decodeEastIR(blob)	A program plus its source map, so loc_ids stay resolvable across processes
Collections larger than memory (v5)
new Beast2Writer(T, sink, opts?)	Append-only writer. .write(batch) emits one segment per non-empty batch — peak memory is ONE batch, never the collection; .finish() writes the terminator and paging index; .segments counts batches. sink is (bytes: Uint8Array) => void
encodeBeast2SegmentsFor(T, opts?): (batches) => Uint8Array	In-memory convenience over the writer
iterBeast2SegmentsFor(T, opts?): (blob) => Generator	Yields one decoded collection per segment — O(segment) decoded memory
openBeast2PagesFor(T, opts?): (blob) => Beast2Pages	Random access: .elementCount and .segmentCount are O(1) from the trailing index; .segment(i) and .element(row) decode only the segment they touch

Example:

import { createWriteStream } from "node:fs";
import {
    ArrayType, StructType, StringType, IntegerType,
    Beast2Writer, iterBeast2SegmentsFor, openBeast2PagesFor, decodeBeast2For,
} from "@elaraai/east";

const Rows = ArrayType(StructType({ id: IntegerType, name: StringType }));

// Write a collection that never exists in memory in full.
const out = createWriteStream("rows.beast2");
const writer = new Beast2Writer(Rows, bytes => out.write(bytes));
for (const batch of batches) writer.write(batch);   // one segment each
writer.finish();

const blob = new Uint8Array(readFileSync("rows.beast2"));

// Read it whole — segments merge on decode.
decodeBeast2For(Rows)(blob);                        // all rows

// Or a batch at a time, holding only one segment.
for (const segment of iterBeast2SegmentsFor(Rows)(blob)) consume(segment);

// Or address a single row without decoding the rest.
const pages = openBeast2PagesFor(Rows)(blob);
pages.elementCount;                                 // O(1), from the index
pages.element(4_000_000);                           // decodes ONE segment

Notes:

• Merging on decode follows the collection: Array concatenates, Set unions, Dict keeps the last occurrence of a key (update semantics).
• write() skips empty batches, so a segment count is never zero.
• Streaming and paging are v5-only — v4 cannot be appended to, by construction.
• The writer defaults to self-contained segments plus an index, which is what makes openBeast2PagesFor and parallel decode possible; pass { selfContained: false } only if you need aliasing to span segments.

Related skills

East is the language inside every other skill's East.function bodies. East itself is pure — load the skill that matches the capability you're adding:

• east-node-std — side effects on Node: files, HTTP (Fetch), crypto, time, random.
• east-node-io — databases (SQL / NoSQL), S3, FTP / SFTP, XLSX / XML, compression.
• east-py-datascience — optimization, ML, Bayesian inference, simulation.
• east-ui — typed UI components returning UIComponentType.
• e3 — run East functions as durable, content-addressed dataflow tasks.
• east-project — author a project-owned platform function (East.platform(...).implement(...)) and wire it into an e3 task via the ./platform export.
• e3-create — scaffold a project (and its custom-platform packages) with npm create @elaraai/{e3,east}.
• east-design — when you have a goal but no architecture yet (start here).