Syntax

The reader is Clojure's, case-sensitive: Foo and foo name different variables. Every identifier is mangled behind a c% prefix on lowering, so no Clojure name can collide with a core form or built-in; a quoted symbol demangles, so 'e2e-foo prints e2e-foo.

Dispatch and comment syntax

, is whitespace, as in Clojure. #! starts a shebang comment on the first line; ; starts a line comment; #_ skips the next form (one before a closing bracket or at the end of the file discards too, so [1 #_ 2] is [1]). A regex literal (#"...") reads to a pattern value (see Regular expressions); #'x reads as (var x), the var of a definition (see var); syntax-quote (`, ~, ~@) is covered in Semantics. Metadata (^, the legacy #^) reads too: on a name or a local it parses and drops, on a vector, map or set literal it attaches like with-meta (see Semantics). A record literal (#ns.Name{...} / #ns.Name[...]) reads to the record over its unevaluated body (see defrecord).

Characters

Characters read as characters: \a, the lowercase newline/space/tab/return/ backspace/formfeed names, \uXXXX and \oNNN. The character after the backslash belongs to the literal whatever it is, so \(, \; and \" read (what pr spells for them), and a backslash ends a literal ([\a\b] is two). Anything else is an Unsupported character refusal. A character prints \a readably (pr) and a plainly (println/str).

Numbers

Integers read in radix: 0xFF hexadecimal, 2r101 and 8r17 arbitrary-radix Nr notation, and a leading-0 octal; the sign applies outside the radix prefix. A shaped token that parses to nothing is an Invalid number refusal.

1M lowers to an exact ratio (0.1M is 1/10), so decimal arithmetic stays exact and prints as the ratio without its mark; a 2N past the long range is a bignum, also printing without its mark. Ratios read as 1/2.

##NaN, ##Inf and ##-Inf read as doubles, in source and under read-string/read, and pr, prn and println print them in the same spelling (also inside a collection); str and format say NaN, Infinity and -Infinity for the bare value. Any other ##name is an Unknown symbolic value refusal. Two NaNs are never =; a NaN used as a map or set key is found by value here, where the oracle finds only the same boxed object.

Booleans, nil and keywords

true, false and nil are self-evaluating; false is a distinct object from nil (see Deviations). A keyword :foo is data holding its spelling verbatim, case-preserved, so :a and :A stay apart; it prints with its colon. A namespaced :a/b is opaque data that prints and compares whole. ::-auto-resolve resolves against the current namespace: ::kw to :my.ns/kw inside (ns my.ns) (:user/kw without one), ::alias/kw through the alias (:require's :as, the namespace's own name, or a known namespace without any require). An unknown alias is an Invalid token refusal. In call position a keyword is the map lookup -- Semantics.

Collection literals

A vector [1 2 3], a map {:a 1}, a set #{1 2} and a quoted list '(1 2 3) read as the literals whose lowering Semantics describes. A set literal refuses a repeated element by spelling (Duplicate key).