Rob_688
0
Is there a language specification for clojure? Something that precisely defines the lexical syntax and grammar in EBNF or something similar?
The closest thing that I could find is the clojure website, but that doesn't really quite meet the requirements of a language spec (despite being an absolutely wonderful resource). If there is no spec, has our BDFL made mention of any plans for one?
Let's look at a syntax error or two:
user=> (defn)
Syntax error macroexpanding clojure.core/defn at (REPL:1:1).
() - failed: Insufficient input at: [:fn-name] spec: :clojure.core.specs.alpha/defn-args
And
user=> (fn [3]) Syntax error macroexpanding clojure.core/fn at (REPL:1:1).
(3) - failed: Extra input at: [:fn-tail :arity-1 :params] spec: :clojure.core.specs.alpha/param-list
3 - failed: vector? at: [:fn-tail :arity-n :params] spec: :clojure.core.specs.alpha/param-list
It is clear that the syntax of the core macros is now (version 1.10) checked using clojure.spec. If and when the Clojure in Clojure project advances, we can expect spec to extend its reach into the compiler proper.
The point is that spec has full EBNF power, so the source code will then contain a full EBNF of the language. The notation is explained in Clojure - clojure.spec: Rationale and Overview:
Sequences
Specs for sequences/vectors use a set of standard regular expression operators, with the standard semantics of regular expressions:
cat - a concatenation of predicates/patterns alt - a choice of one among a set of predicates/patterns * - zero or more occurrences of a predicate/pattern + - one or more ? - one or none & - takes a regex op and further constrains it with one or more predicates
When will this happen? My (utterly uninformed) impression is that the core team are drowning in alligators and have almost forgotten their original intention to drain this swamp.
A previous answer referring to spec in general terms for Clojure 1.9 was deleted. I think its use to define and check macro syntax is new with 1.10.