Parameters

parameters extracts every parameter reference and non-built-in function call present in an expression.

Function signatures

function parameters(expression: string | LogicalExpression): {
  names: Set<string>;
  functions: Set<string>;
};
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Return value

Built-in functions (Abs, Sin, if, ifs, etc.) are excluded from functions because they are always available without configuration.

Examples

Extract parameter names

import { parameters } from "@imogenz/escalc";

parameters("[price] * (1 + [taxRate]) - [discount]");
// => { names: Set { 'price', 'taxRate', 'discount' }, functions: Set {} }
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Identify custom functions

parameters("myFn([x]) + Abs([x]) + anotherFn([y])");
// => { names: Set { 'x', 'y' }, functions: Set { 'myFn', 'anotherFn' } }
// Abs is built-in, so it is not included in functions
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Validate that all parameters are supplied

import { parameters, evaluate } from "@imogenz/escalc";

function safeEvaluate(expr: string, values: Record<string, unknown>) {
  const { names } = parameters(expr);
  const missing = [...names].filter((n) => !(n in values));
  if (missing.length) {
    throw new Error(`Missing parameters: ${missing.join(", ")}`);
  }
  return evaluate(expr, { params: new Map(Object.entries(values)) });
}
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Handling invalid expressions

import { parameters } from "@imogenz/escalc";

try {
  const result = parameters(userInput);
  console.log("Parameters:", [...result.names]);
} catch (error) {
  console.error("Expression is invalid", error);
}
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