f3084f8043
A type-aware audit (~190 collection expressions vs reference Clojure) found four divergences the corpus missed — value-equality (= [0 1] '(0 1)) hides type and laziness differences. Fixed, with type-predicate + over-infinite corpus rows that pin them. - partition-all [n coll] built vector chunks; JVM chunks are seqs. (The [n step coll] arity was already correct, as is the partition-all transducer, whose chunks are vectors in JVM too.) Now builds seq chunks. - replace always returned a vector (mapv) and was eager; JVM is type-preserving — a vector maps to a vector, any other seqable to a lazy seq. - sequence eagerly realized its source (into-xform), so (first (sequence (map inc) (range))) hung. Rewrote as a transformer iterator: pull one input at a time, buffer the step outputs, emit lazily, run the completion to flush a stateful xform. eduction builds on it (lazy, no longer an eager vector). - mapcat and (apply concat coll-of-colls) hung over an infinite source because jolt-apply seq->lists the trailing arg and mapcat seq->lists the map result. Added lazy-concat-seq (lazily flatten a seq of colls); mapcat uses it directly, and apply special-cases concat (its result is lazy) to route through it. Docs: a cross-cutting return-type + laziness contract in docs/spec/09-core-library; SPEC.md notes that = masks type/laziness so they need predicate / over-infinite rows. EBNF is reader syntax only — unaffected. Seed change (partition-all/replace/eduction are clojure.core overlay) -> re-mint; selfhost holds. make test + shakesmoke + buildsmoke green, 0 new divergences. Co-authored-by: Yogthos <yogthos@gmail.com>
208 lines
7.9 KiB
Markdown
208 lines
7.9 KiB
Markdown
# §9 The Core Library
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**Status**: entry format fixed; exemplars for `first`, `reduce`, `parse-uuid`.
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The full portable surface (≈500 vars after classification, dashboard in
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`coverage.md`) is filled in chapter-by-chapter using this format.
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Entries specify *behavioral contracts*, not implementations. Performance
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characteristics are specified only where the language community relies on
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them (e.g. vector `nth` is "effectively constant time" — SHOULD-level).
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---
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## Collection return types & laziness (cross-cutting)
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Two contracts hold across the sequence library and are not restated per entry.
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**Return-type fidelity.** A function returns the same *kind* of collection the
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reference does — value equality is not enough, since `(= [0 1] '(0 1))`.
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- Sequence transformations return **seqs** (lazy unless noted): `map`, `filter`,
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`remove`, `keep`, `mapcat`, `take`/`drop` and their `-while` forms, `partition`,
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`partition-all`, `partition-by`, `interpose`, `dedupe`, `distinct`, `concat`,
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`reductions`, `cons`, `rest`, `sequence`. The *elements* of `partition` /
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`partition-all` / `partition-by` are themselves seqs, not vectors.
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- The vector variants return **vectors**: `mapv`, `filterv`, `vec`, `subvec`,
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`partitionv`, `partitionv-all`, `splitv-at`. `split-at` / `split-with` return a
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2-vector `[take drop]`. A transducer applied eagerly (`into []`, the
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`partition-all` transducer's chunks) yields vectors.
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- Type-preserving functions return the input's type: `replace` over a vector is a
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vector, over any other seqable a (lazy) seq; `empty`/`into (empty coll)` keep the
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collection kind; `set`/`into #{}` return sets; `into {}`/`select-keys`/`zipmap`/
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`frequencies`/`group-by`/`merge` return maps (`group-by` values are vectors).
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**Laziness.** The lazy sequence functions — including `sequence`, `eduction`, and
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`mapcat` — MUST consume their source incrementally and so terminate on an infinite
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or unbounded source when only a prefix is demanded: `(first (sequence (map inc)
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(range)))` and `(take n (mapcat f (range)))` return without realizing the whole
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source. `(apply concat coll-of-colls)` is likewise lazy in its argument seq. The
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eager consumers (`reduce`, `into`, `count`, `vec`, `doall`) realize the demanded
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portion fully.
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These are exercised by the `seq / lazy over infinite` and the per-fn type-predicate
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rows in the conformance corpus.
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---
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### first — since 1.0
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```
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(first coll)
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```
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**Semantics**
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- S1. MUST return the first element of `(seq coll)`.
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- S2. If `(seq coll)` is `nil` (i.e. `coll` is empty or `nil`), MUST return
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`nil`.
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- S3. MUST accept anything *seqable* (§5): seqs, lists, vectors, maps
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(yielding map entries), sets, strings (yielding characters), `nil`.
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- S4. On a lazy sequence, MUST realize at most the first element (§5
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laziness contract).
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**Edge cases**
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- E1. `(first nil)` ⇒ `nil`; `(first [])` ⇒ `nil`; `(first "")` ⇒ `nil`.
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- E2. A `nil` or `false` first *element* is returned as-is — callers cannot
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distinguish "empty" from "first element is nil" via `first` alone (that is
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what `seq` is for).
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- E3. On a map, the element is a map entry; on an unordered collection (map,
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set) *which* element is first is implementation-defined but MUST be
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consistent with that collection's seq order for the same collection value.
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**Errors**
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- X1. A non-seqable argument (e.g. a number) MUST throw.
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**Examples**
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```clojure
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(first [1 2 3]) ;=> 1
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(first '()) ;=> nil
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(first "ab") ;=> \a
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(first {:a 1}) ;=> [:a 1]
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(first [nil 2]) ;=> nil
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```
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**Conformance**
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S1–S3, E1–E2 → jolt `sequences-spec` "seq / access"; clojure-test-suite
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`core_test/first.cljc`. S4 → jolt `lazy-seqs-spec` counter cases. X1 →
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clojure-test-suite `core_test/first.cljc` (throwing cases).
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---
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### reduce — since 1.0
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```
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(reduce f coll)
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(reduce f init coll)
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```
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**Semantics**
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- S1. With `init`: MUST return `init` if `(seq coll)` is nil; otherwise MUST
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return `(f … (f (f init e₁) e₂) … eₙ)`, applying `f` left-to-right over the
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elements, exactly once each.
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- S2. Without `init`: if `coll` is empty, MUST return `(f)` (f called with
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no arguments); if `coll` has one element, MUST return that element
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*without calling `f`*; otherwise as S1 with `init = e₁` over `e₂…eₙ`.
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- S3. **Reduced short-circuit**: if any intermediate result is a `reduced`
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value, iteration MUST stop and the dereferenced value MUST be returned
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immediately; `f` MUST NOT be called again.
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- S4. `reduce` is eager: it MUST fully realize the consumed portion of a
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lazy `coll` (to the end, or to the `reduced` point).
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**Edge cases**
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- E1. `(reduce f nil)` ⇒ `(f)`; `(reduce f init nil)` ⇒ `init`.
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- E2. A `reduced` value as the *initial* `init` is NOT unwrapped before the
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first call in the reference — ⚠ under-documented; differential result to
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pin down and test before this entry is marked verified.
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- E3. Visit order over maps is entry order of the map's seq;
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over vectors/lists/seqs it is sequential order (normative).
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**Errors**
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- X1. Without `init`, on an empty coll, if `f` has no zero-arg arity the
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call `(f)` MUST throw (arity error).
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**Examples**
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```clojure
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(reduce + [1 2 3 4]) ;=> 10
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(reduce + 10 [1 2 3 4]) ;=> 20
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(reduce + []) ;=> 0 ; (+) is 0
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(reduce + [5]) ;=> 5 ; f not called
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(reduce (fn [a x] (if (> a 2) (reduced a) (+ a x))) 0 [1 2 3 4 5]) ;=> 3
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```
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**Conformance**
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S1–S3, E1 → jolt `sequences-spec` "map filter reduce" group +
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`transducers-spec` "reduce honors reduced"; clojure-test-suite
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`core_test/reduce.cljc`. S2 (single-element, f-not-called) → jolt conformance
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"reduce single no init". E2 → UNVERIFIED (differential test to add). S4 →
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`lazy-seqs-spec`.
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---
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### parse-uuid — since 1.11
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```
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(parse-uuid s)
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```
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**Semantics**
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- S1. If `s` is a string in canonical UUID form — five groups of hex digits
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of lengths 8, 4, 4, 4, 12 separated by `-` — MUST return a UUID value `u`
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such that `(uuid? u)` is true and `(str u)` is the lowercase form of `s`.
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- S2. Parsing MUST be case-insensitive and equality on the results
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case-insensitive: `(= (parse-uuid s) (parse-uuid (upper-case s)))` is true.
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- S3. If `s` is a string not in canonical form, MUST return `nil`.
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⚠ reference-divergence: reference Clojure (java.util.UUID) additionally
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accepts non-canonical forms like `"0-0-0-0-0"`; ClojureScript and other
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dialects are strict. This spec adopts **strict** (the cross-dialect
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behavior); the reference's permissiveness is recorded as host leniency.
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- S4. UUID values MUST support value equality, hashing (usable as map keys
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and set members), `str` (lowercase canonical form), and print as the
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tagged literal `#uuid "…"` such that the printed form reads back equal
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(§2 tagged literals).
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**Edge cases**
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- E1. `""`, over-long, truncated, non-hex characters, and misplaced dashes
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⇒ `nil`.
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**Errors**
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- X1. A non-string argument MUST throw.
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**Examples**
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```clojure
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(parse-uuid "b6883c0a-0342-4007-9966-bc2dfa6b109e") ;=> #uuid "b6883c0a-…"
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(uuid? *1) ;=> true
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(parse-uuid "df0993") ;=> nil
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(parse-uuid 1000) ;; throws
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```
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**Conformance**
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S1–S4, E1, X1 → jolt `uuid-spec` (30 cases) + 6 three-path conformance
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cases; clojure-test-suite `core_test/parse_uuid.cljc`,
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`core_test/uuid_qmark.cljc`, `core_test/random_uuid.cljc`.
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---
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## Authoring notes
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- Source examples from the ClojureDocs export (`clojuredocs-export.edn`,
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648 core vars have community examples) — but every example is verified
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against the reference before inclusion.
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- When writing an entry surfaces a behavior question, settle it by
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differential test first; if dialects split, that's a classification
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decision (host-dependent / divergence note), not a coin flip.
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- An entry is **Verified** when no field carries UNVERIFIED; `coverage.md`
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tracks per-var status.
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