[![NPM version][npm-image]][npm-url] ## Description likescheme is a plain Javascript implementation of the functional prefix-notation Scheme-like interpreted language. It evaluates functional logic statements represented as a string or an object in a provided execution environment scope. Syntaxically, likescheme is somewhat similar to Tcl language. ### Use Case #### Move logic from code to configuration. __likescheme__ lets you encode functional statements directly into the configuration layer of your app or service when coding it in Javascript is not feasible due to complexity or security considerations. #### Examples: - UI elements visibility logic - workflow routing rules - data or ETL mapping logic ### Why not Lisp or Scheme or Lua? The following popular plain Javascript implementation of Lisp, Scheme or Lua could be considered an alternative. - [LIPS](https://lips.js.org/) - [Lua](https://www.npmjs.com/package/lua-interpreter) However, we decided to create __likescheme__ to limit functionality to conditional and aggregate operations only, which reduces complexity, the learning curve, and makes it safer. ## Installation ```bash npm i likescheme ``` ## Usage ### import #### ECMAScript Module ```javascript import {evaluate} from 'likescheme'; ``` #### CommonJS Module ```javascript const likescheme = require('likescheme'); const evaluate = likescheme.evaluate; ``` #### In-browser Use ```html ... ... ... ... ... ``` ### evaluate Evaluates __code__ in the context of the provided __data__ object. ```javascript evaluate ( code, // string, e.g. [gt [get amount] 100.0] // or Array, e.g. ['gt', ['get', 'amount']], // or JSON, e.g. {operator: 'gt', args: [{operator: 'get', args: ['amount']}, 100.0]} data, // object, JSON, optional, e.g. {price: 150.0}, nested objects and lists are supported (see examples) strict // boolean, optional, default=true, if true, unknown variable throws error, else they are set to undefined ) ``` ### Examples ```javascript evaluate( "[and [veq 'order.product' 'apple'] [vge 'order.quantity 1]]", { order: { product: 'apple', quantity: 1 } } ); // returns true ``` #### More Examples - See more examples [here](./examples) ### parse Converts __code__ from __string__ to __Array__ (list) representation. ```javascript parse(code) ``` ### Examples ```javascript import {parse} from 'likescheme'; parse("[and [veq 'order.product' 'apple'] [vge 'order.quantity' 1]]"); // returns ['and', [ 'veq', 'order.product', 'apple' ], [ 'vge', 'order.quantity', 1]] ``` ### compile Converts __code__ from __Array__ to __JSON__ representation. ```javascript compile( ['and', [ 'veq', 'order.product', 'apple' ], [ 'vge', 'order.quantity', 1]]); // returns { operator: 'and', args: [ { operator: 'veq', args: [ 'order.product', 'apple' ] }, { operator: 'vge', args: [ 'order.quantity', 1 ] } ] } ``` ## Functions - `get key` - returns the value of the data object property referenced by __key__. Nested objects supported via 'dot' notation. - `"[get 'product.name']"` - `['get', 'product.name']` - `{operator: 'get', args: ['product.name']}` - `list 'value1' ... ` - returns the list (array) of values - `"[list 'apple' 'banana' 'pear']"` - `['list', 'apple', 'banana', 'pear' ]` - `{operator: 'list', args: ['apple', 'banana', 'pear']}` - `in value list` - returns __true__ if the __value__ is in the list provided in the second argument - `"[in [get 'product.name'] [list 'apple' 'banana' 'pear']]"` - `['in', ['get', 'product.name'], ['list', 'apple', 'banana', 'pear']]` - `{operator: 'in', args: [{operator: 'get', args:['product.name']}, {operator: 'list', args: ['apple', 'banana', 'pear']}]}` - `eq|ne|lt|gt|le|ge value1 value2` - returns __true__ if __value1__ is equal|not-equal|less-then|greater-then|less-or-equal-then|greater-or-equal-then to __value2__ - `"[eq [get 'product.name'] 'apple']"` - `['eq', ['get', 'product.name'], 'apple']` - `{operator: 'eq', args: [{operator: 'get', args: ['product.name']}, 'apple']}` - example: `{operator: 'eq', args: [{operator: 'get', args: ['product.name']}, 'apple']}` - `isy|isn|isu key` - syntaxical sugar - returns __true__ if the value of the data object property referenced by __key__ is 'truthy', 'falsy' or unknown respectively - `"[isy 'isTaxFree']"` - `['isy', 'isTaxFree']` - `{operator: 'isy', args: [ 'isTaxFree' ]}` - `not value` - returns the boolean 'not' of its argument - `"[not [in [get 'product.name'] [list 'apple' 'banana' 'pear']]]"` - `['not', ['in', ['get', 'product.name'], ['list', 'apple', 'banana', 'pear']]]` - `{operator: 'not', args: [{operator: 'in', args: [{operator: 'get', args: ['product.name']}, {operator: 'list', args: ['apple', 'banana', 'pear']}]}]}` - `and|or value1, ...` - returns the boolean 'and|or' of its arguments - `"[and [isy 'isRound'] [isy 'isRed']]"` - `['and', ['isy', 'isRound'], ['isy', 'isRed']]` - `{operator: 'and', args: [{operator: 'isy', args: [Array]}, {operator: 'isy', args: [Array]}]}` - `undefined|null|true|false` - takes no arguments, returns __undefined__, __null__, __true__, and __false__ respectively - `isundefined key` - returns __true__ if the data object does not contain the property referenced by __key__; this function is not affected by the __strict__ argument value. - note: to test for the actual undefined value of an existing data object property, use `[eq [get 'myVar'] [undefined]]` - `veq|vne|vlt|vgt|vle|vge key value` - syntaxical sugar - returns __true__ if the value of the data object property referenced by __key__ is equal|not-equal|less-then|greater-then|less-or-equal-then|greater-or-equal-then to __value__ - `"[veq 'product.name' 'apple']"` - `['veq', 'product.name', 'apple']` - `{operator: 'veq', args: [ 'product.name', 'apple' ]}` - `vin key list` - syntaxical sugar - returns __true__ if the value of the data object propert referenced by __key__ is in the list provided in the second argument - `"[vin 'product.name' [list 'apple' 'banana' 'pear']]"` - `['vin', 'product.name', ['list', 'apple', 'banana', 'pear']]` - `{operator: 'vin', args: ['product.name', {operator: 'list', args: ['apple', 'banana', 'pear']}]}` - `bw value fromValue thruValue` - returns __true__ if __value__ is between __fromValue__ and __thruValue__, inclusive on both ends - `"[bw [get 'product.price'] 5.0 15.0]"` - `min|max list` - returns min|max value in the __list__ - `"[min [list 1 10 11 101]]"` - `map value (key1, value1, ... keyX, valueX) defaultValue` - returns __valueX__, which corresponds to the __keyX__, which is equal to __value__ or __defaultValue__ if such __keyX__ does not exist - `"[map [get 'product.name'] [list 'apple' 'fruit' 'banana' 'fruit' 'tomato' 'vegetable'] 'unknown']"` - returns `fruit` if `product.name` is `apple` - `days value1 value2` - returns the number of days between the two dates represented by __value1__ (from date) and __value2__ (thru date), exclusive of thru date - the date value is expected to be a string parseable by Javascript `Date.parse()` - if the date value cannot be parsed, the function returns `NaN` - `"[days '2022-06-01' '2022-06-17']"` - returns `16` - `code: "[days [get 'fromDate'] [get 'endDate']]", data: {fromDate: '2022-06-17', endDate: '2022-06-01'}` - returns `-16` - `vdays key1 key2` - syntaxical sugar for `days` - returns the number of days between the two dates contained in the objects referenced by __key1__ and __key2__ - `code: "[vdays 'fromDate' 'endDate']", data: {fromDate: '2022-06-01', endDate: '2022-06-17'}` - returns `16` - `today` - returns today's date in YYYY-MM-DD format - `"[days [today] [today]]"` - return `0` - `join|split|uniq|usort|lindex|lrange` - for these list functions see [Examples](./examples) and [the actual code](./interpreter.cjs) - `sum|mult|div|neg|rem|sub` - for these aggregate functions see [Examples](./examples) and [the actual code](./interpreter.cjs) [npm-url]: https://www.npmjs.com/package/likescheme [npm-image]: https://img.shields.io/npm/v/likescheme.svg