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Common Expression Language\n\nThe Common Expression Language (CEL) implements common semantics for expression\nevaluation, enabling different applications to more easily interoperate.\n\nKey Applications\n\n*   Security policy: organizations have complex infrastructure and need common\n    tooling to reason about the system as a whole\n*   Protocols: expressions are a useful data type and require interoperability\n    across programming languages and platforms.\n\n\nGuiding philosophy:\n\n1.  Keep it small \u0026 fast.\n    *   CEL evaluates in linear time, is mutation free, and not Turing-complete.\n        This limitation is a feature of the language design, which allows the\n        implementation to evaluate orders of magnitude faster than equivalently\n        sandboxed JavaScript.\n2.  Make it extensible.\n    *   CEL is designed to be embedded in applications, and allows for\n        extensibility via its context which allows for functions and data to be\n        provided by the software that embeds it.\n3.  Developer-friendly.\n    *   The language is approachable to developers. The initial spec was based\n        on the experience of developing Firebase Rules and usability testing\n        many prior iterations.\n    *   The library itself and accompanying toolings should be easy to adopt by\n        teams that seek to integrate CEL into their platforms.\n\nThe required components of a system that supports CEL are:\n\n*   The textual representation of an expression as written by a developer. It is\n    of similar syntax to expressions in C/C++/Java/JavaScript\n*   A representation of the program's abstract syntax tree (AST).\n*   A compiler library that converts the textual representation to the binary\n    representation. This can be done ahead of time (in the control plane) or\n    just before evaluation (in the data plane).\n*   A context containing one or more typed variables, often protobuf messages.\n    Most use-cases will use `attribute_context.proto`\n*   An evaluator library that takes the binary format in the context and\n    produces a result, usually a Boolean.\n\nFor use cases which require persistence or cross-process communcation, it is\nhighly recommended to serialize the type-checked expression as a protocol\nbuffer. The CEL team will maintains canonical protocol buffers for ASTs and\nwill keep these versions identical and wire-compatible in perpetuity:\n\n*  [CEL canonical](https://github.com/cel-expr/cel-spec/tree/master/proto/cel/expr)\n*  [CEL v1alpha1](https://github.com/googleapis/googleapis/tree/master/google/api/expr/v1alpha1)\n\n\nExample of boolean conditions and object construction:\n\n``` c\n// Condition\naccount.balance \u003e= transaction.withdrawal\n    || (account.overdraftProtection\n    \u0026\u0026 account.overdraftLimit \u003e= transaction.withdrawal  - account.balance)\n\n// Object construction\ncommon.GeoPoint{ latitude: 10.0, longitude: -5.5 }\n```\n\nFor more detail, see:\n\n*   [Introduction](doc/intro.md)\n*   [Language Definition](doc/langdef.md)\n\nReleased under the [Apache License](LICENSE).\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fcel-expr%2Fcel-spec","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fcel-expr%2Fcel-spec","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fcel-expr%2Fcel-spec/lists"}