cel-parser: A Clojure parser for the CEL language

This library provides a parser and evaluation engine for the language specified in https://github.com/google/cel-spec/.

Usage

The simplest way to run through a CEL expression is to use exoscale.cel.parser/parse-eval which parses an expression into a program and runs it against the provided input. Input is provided in the form of bindings: a map of symbol to install in the program's namespace to its value.

(parse-eval "true")
(parse-eval {:bindings {:x "world"}} "'hello, ' + x + '!'")

When repeatedly running the same expression, the action can be decomposed in two phases, first building the program with exoscale.cel.parser/make-program, and then running it with exoscale.cel.parser/eval-for:

(def my-program (make-program "'hello, ' + x + '!'"))

(eval-for my-program {:x "world"})

When execution results in an error, an exception is returned, not thrown by default. To throw upon error returns, throw-on-error? may be added to the input map.

Limitations

The following is currently not supported in this parser:

• Namespaces
• Namespaced keys in maps; Resulting CEL expressions will get unqualified string keys
• Protobuf object creation; For now, objects are expected to be supplied as maps

Language support

The majority of the language functionality is supported and validated through tests generated by the testdata https://github.com/google/cel-spec/tree/master/tests/simple/testdata

Some small divergences exist:

• Aggregate types may return false instead of an overload error for some comparisons (notably maps).
• Integer conversions are slighlty more relaxed than the spec allows for, for instance int(-9223372036854775807.0) yields a valid int in this parser but is expected to fail in the spec