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feat(patterns): pattern-based compression
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,292 @@ | ||
| // @ts-check | ||
| import { assertChecker, makeTagged, passStyleOf } from '@endo/marshal'; | ||
| import { recordNames, recordValues } from '@endo/marshal/src/encodePassable.js'; | ||
|
|
||
| import { | ||
| kindOf, | ||
| assertPattern, | ||
| maybeMatchHelper, | ||
| matches, | ||
| checkMatches, | ||
| mustMatch, | ||
| } from './patternMatchers.js'; | ||
| import { isKey } from '../keys/checkKey.js'; | ||
| import { keyEQ } from '../keys/compareKeys.js'; | ||
|
|
||
| /** @typedef {import('@endo/pass-style').Passable} Passable */ | ||
| /** @typedef {import('../types.js').Compress} Compress */ | ||
| /** @typedef {import('../types.js').MustCompress} MustCompress */ | ||
| /** @typedef {import('../types.js').Decompress} Decompress */ | ||
| /** @typedef {import('../types.js').MustDecompress} MustDecompress */ | ||
| /** @typedef {import('../types.js').Pattern} Pattern */ | ||
|
|
||
| const { fromEntries } = Object; | ||
| const { Fail, quote: q } = assert; | ||
|
|
||
| const isNonCompressingMatcher = pattern => { | ||
| const patternKind = kindOf(pattern); | ||
| if (patternKind === undefined) { | ||
| return false; | ||
| } | ||
| const matchHelper = maybeMatchHelper(patternKind); | ||
| return matchHelper && matchHelper.compress === undefined; | ||
| }; | ||
|
|
||
| /** | ||
| * When, for example, all the specimens in a given store match a | ||
| * specific pattern, then each of those specimens must contain the same | ||
| * literal superstructure as their one shared pattern. Therefore, storing | ||
| * that literal superstructure would be redumdant. If `specimen` does | ||
| * match `pattern`, then `compress(specimen, pattern)` will return a bindings | ||
| * array which is hopefully more compact than `specimen` as a whole, but | ||
| * carries all the information from specimen that cannot be derived just | ||
| * from knowledge that it matches this `pattern`. | ||
| * | ||
| * @type {Compress} | ||
| */ | ||
| const compress = (specimen, pattern) => { | ||
| if (isNonCompressingMatcher(pattern)) { | ||
| if (matches(specimen, pattern)) { | ||
| return harden({ compressed: specimen }); | ||
| } | ||
| return undefined; | ||
| } | ||
|
|
||
| // Not yet frozen! Used to accumulate bindings | ||
| const bindings = []; | ||
| const emitBinding = binding => { | ||
| bindings.push(binding); | ||
| }; | ||
| harden(emitBinding); | ||
|
|
||
| /** | ||
| * @param {Passable} innerSpecimen | ||
| * @param {Pattern} innerPattern | ||
| * @returns {boolean} | ||
| */ | ||
| const compressRecur = (innerSpecimen, innerPattern) => { | ||
| assertPattern(innerPattern); | ||
| if (isKey(innerPattern)) { | ||
| return keyEQ(innerSpecimen, innerPattern); | ||
| } | ||
| const patternKind = kindOf(innerPattern); | ||
| const specimenKind = kindOf(innerSpecimen); | ||
| switch (patternKind) { | ||
| case undefined: { | ||
| return false; | ||
| } | ||
| case 'copyArray': { | ||
| if ( | ||
| specimenKind !== 'copyArray' || | ||
| innerSpecimen.length !== innerPattern.length | ||
| ) { | ||
| return false; | ||
| } | ||
| return innerPattern.every((p, i) => compressRecur(innerSpecimen[i], p)); | ||
| } | ||
| case 'copyRecord': { | ||
| if (specimenKind !== 'copyRecord') { | ||
| return false; | ||
| } | ||
| const specimenNames = recordNames(innerSpecimen); | ||
| const pattNames = recordNames(innerPattern); | ||
|
|
||
| if (specimenNames.length !== pattNames.length) { | ||
| return false; | ||
| } | ||
| const specimenValues = recordValues(innerSpecimen, specimenNames); | ||
| const pattValues = recordValues(innerPattern, pattNames); | ||
|
|
||
| return pattNames.every( | ||
| (name, i) => | ||
| specimenNames[i] === name && | ||
| compressRecur(specimenValues[i], pattValues[i]), | ||
| ); | ||
| } | ||
| case 'copyMap': { | ||
| if (specimenKind !== 'copyMap') { | ||
| return false; | ||
| } | ||
| const { | ||
| payload: { keys: pattKeys, values: valuePatts }, | ||
| } = innerPattern; | ||
| const { | ||
| payload: { keys: specimenKeys, values: specimenValues }, | ||
| } = innerSpecimen; | ||
| // TODO BUG: this assumes that the keys appear in the | ||
| // same order, so we can compare values in that order. | ||
| // However, we're only guaranteed that they appear in | ||
| // the same rankOrder. Thus we must search one of these | ||
| // in the other's rankOrder. | ||
| if (!keyEQ(specimenKeys, pattKeys)) { | ||
| return false; | ||
| } | ||
| return compressRecur(specimenValues, valuePatts); | ||
| } | ||
| default: | ||
| { | ||
| const matchHelper = maybeMatchHelper(patternKind); | ||
| if (matchHelper) { | ||
| if (matchHelper.compress) { | ||
| const subCompressedRecord = matchHelper.compress( | ||
| innerSpecimen, | ||
| innerPattern.payload, | ||
| compress, | ||
| ); | ||
| if (subCompressedRecord === undefined) { | ||
| return false; | ||
| } else { | ||
| emitBinding(subCompressedRecord.compressed); | ||
| return true; | ||
| } | ||
| } else if (matches(innerSpecimen, innerPattern)) { | ||
| assert(isNonCompressingMatcher(innerPattern)); | ||
| emitBinding(innerSpecimen); | ||
| return true; | ||
| } else { | ||
| return false; | ||
| } | ||
| } | ||
| } | ||
| throw Fail`unrecognized kind: ${q(patternKind)}`; | ||
| } | ||
| }; | ||
|
|
||
| if (compressRecur(specimen, pattern)) { | ||
| return harden({ compressed: bindings }); | ||
| } else { | ||
| return undefined; | ||
| } | ||
| }; | ||
| harden(compress); | ||
|
|
||
| /** | ||
| * `mustCompress` is to `compress` approximately as `fit` is to `matches`. | ||
| * Where `compress` indicates pattern match failure by returning `undefined`, | ||
| * `mustCompress` indicates pattern match failure by throwing an error | ||
| * with a good pattern-match-failure diagnostic. Thus, like `fit`, | ||
| * `mustCompress` has an additional optional `label` parameter to be used on | ||
| * the outside of that diagnostic if needed. If `mustCompress` does return | ||
| * normally, then the pattern match succeeded and `mustCompress` returns a | ||
| * valid compressed value. | ||
| * | ||
| * @type {MustCompress} | ||
| */ | ||
| export const mustCompress = (specimen, pattern, label = undefined) => { | ||
| const compressedRecord = compress(specimen, pattern); | ||
| if (compressedRecord !== undefined) { | ||
| return compressedRecord.compressed; | ||
| } | ||
| // `compress` is validating, so we don't need to redo all of `mustMatch`. | ||
| // We use it only to generate the error. | ||
| // Should only throw | ||
| checkMatches(specimen, pattern, assertChecker, label); | ||
| throw Fail`internal: ${label}: inconsistent pattern match: ${q(pattern)}`; | ||
| }; | ||
| harden(mustCompress); | ||
|
|
||
| /** | ||
| * `decompress` reverses the compression performed by `compress` | ||
| * or `mustCompress`, in order to recover the equivalent | ||
| * of the original specimen from the `bindings` array and the `pattern`. | ||
| * | ||
| * @type {Decompress} | ||
| */ | ||
| const decompress = (compressed, pattern) => { | ||
| if (isNonCompressingMatcher(pattern)) { | ||
| return compressed; | ||
| } | ||
|
|
||
| assert(Array.isArray(compressed)); | ||
| passStyleOf(compressed) === 'copyArray' || | ||
| Fail`Pattern ${pattern} expected bindings array: ${compressed}`; | ||
| let i = 0; | ||
| const takeBinding = () => { | ||
| i < compressed.length || | ||
| Fail`Pattern ${q(pattern)} expects more than ${q( | ||
| compressed.length, | ||
| )} bindings: ${compressed}`; | ||
| const binding = compressed[i]; | ||
| i += 1; | ||
| return binding; | ||
| }; | ||
| harden(takeBinding); | ||
|
|
||
| const decompressRecur = innerPattern => { | ||
| assertPattern(innerPattern); | ||
| if (isKey(innerPattern)) { | ||
| return innerPattern; | ||
| } | ||
| const patternKind = kindOf(innerPattern); | ||
| switch (patternKind) { | ||
| case undefined: { | ||
| throw Fail`decompress expected a pattern: ${q(innerPattern)}`; | ||
| } | ||
| case 'copyArray': { | ||
| return harden(innerPattern.map(p => decompressRecur(p))); | ||
| } | ||
| case 'copyRecord': { | ||
| const pattNames = recordNames(innerPattern); | ||
| const pattValues = recordValues(innerPattern, pattNames); | ||
| const entries = pattNames.map((name, j) => [ | ||
| name, | ||
| decompressRecur(pattValues[j]), | ||
| ]); | ||
| // Reverse so printed form looks less surprising, | ||
| // with ascenting rather than descending property names. | ||
| return harden(fromEntries(entries.reverse())); | ||
| } | ||
| case 'copyMap': { | ||
| const { | ||
| payload: { keys: pattKeys, values: valuePatts }, | ||
| } = innerPattern; | ||
| return makeTagged( | ||
| 'copyMap', | ||
| harden({ | ||
| keys: pattKeys, | ||
| values: valuePatts.map(p => decompressRecur(p)), | ||
| }), | ||
| ); | ||
| } | ||
| default: | ||
| { | ||
| const matchHelper = maybeMatchHelper(patternKind); | ||
| if (matchHelper) { | ||
| if (matchHelper.decompress) { | ||
| const subCompressed = takeBinding(); | ||
| return matchHelper.decompress( | ||
| subCompressed, | ||
| innerPattern.payload, | ||
| decompress, | ||
| ); | ||
| } else { | ||
| assert(isNonCompressingMatcher(innerPattern)); | ||
| return takeBinding(); | ||
| } | ||
| } | ||
| } | ||
| throw Fail`unrecognized pattern kind: ${q(patternKind)} ${q( | ||
| innerPattern, | ||
| )}`; | ||
| } | ||
| }; | ||
|
|
||
| return decompressRecur(pattern); | ||
| }; | ||
| harden(decompress); | ||
|
|
||
| /** | ||
| * `decompress` reverses the compression performed by `compress` | ||
| * or `mustCompress`, in order to recover the equivalent | ||
| * of the original specimen from `compressed` and `pattern`. | ||
| * | ||
| * @type {MustDecompress} | ||
| */ | ||
| export const mustDecompress = (compressed, pattern, label = undefined) => { | ||
| const value = decompress(compressed, pattern); | ||
| // `decompress` does some checking, but is not validating, so we | ||
| // need to do the full `mustMatch` here to validate as well as to generate | ||
| // the error if invalid. | ||
| mustMatch(value, pattern, label); | ||
| return value; | ||
| }; |
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