Coming from Clojure

clove aims to behave like JVM Clojure, and when the two disagree, that's a bug in clove unless it's listed here. We check this with a corpus of 545 expressions whose output must match JVM Clojure's, and a fuzzer that runs random expressions through clove and babashka every night.

There is no JVM, so there is no Java. The classes scripts reach for first are modeled in C or in clove: java.io.File, String and Character methods, Math, java.util collections, java.time.LocalDate and Instant, clojure.java.shell/sh. They cover the common methods, not the whole class. Libraries that wrap a specific Java library (an XML parser, a JDBC driver) won't run until someone ports that library.

Differences you might hit

Strings index by codepoint. count, nth, subs and seq agree with what you see on screen, where the JVM counts UTF-16 code units.

Hash maps keep insertion order at any size. The JVM agrees up to 8 keys and then switches to hash order. Don't rely on either: if order matters, use sorted-map.

Syntax quote doesn't qualify symbols. On the JVM, map reads as clojure.core/map; here it stays map. This matters only to macros that inspect their own expansion.

Floating-point division by zero gives infinity or NaN, as compiled Clojure does with primitive doubles. Boxed JVM math, and babashka, throw instead.

There is no separate BigInteger. biginteger returns a BigInt, which does the same arithmetic but prints with an N.

Namespaces

ns, require with :as and :refer, *ns*, ns-publics and ^:private all work, and multi-file libraries load. Underneath, though, there is one global table of names with per-namespace aliases, and a namespace is just its symbol ((find-ns 'user) returns user). Top-level definitions in user stay visible from other namespaces, which real Clojure would not allow.

Smaller things

• catch dispatches on exception class where clove knows it: ex-info, the (IllegalArgumentException. ...) constructors, arithmetic errors, index out of bounds, stack overflow. Other interpreter errors match any catch except ExceptionInfo, AssertionError and Error.
• Seqs realize in chunks of 32, as on the JVM, but chunked-seq? is always false.
• Nested syntax quote doesn't work. Auto-gensym (x#) does.
• Tagged literals stop at #inst and #uuid; *data-readers* isn't consulted.
• tap> calls taps on the spot instead of queuing them for a background thread.
• (?i) in a regex folds ASCII case only.
• cl-format covers the common directives but not ~<~> justification.
• Host objects (File, Date, UUIDs, reify instances) are maps underneath, so map? is true of them.

Things clove adds

• Proper tail calls everywhere, not just through recur.
• #?(:clove ...) in reader conditionals.
• (dbg x), or #p x, prints a form and its value and returns the value.
• The FFI and JIT: call C from clove, or compile a numeric function to machine code.
• Coroutines (coro/new, coro/yield), which core.async runs on.

The README's divergence list is the full version of this page.