sexp-template/src/env.js

const AST = require('../src/ast')

module.exports = class Env {
  constructor(parent = null) {
    if (parent) {
      this.data = parent.data
    } else {
      this.data = {
        '+': (a, b) => new AST.Number({ value: a + b }),
        '-': (a, b) => new AST.Number({ value: a - b }),
        '*': (a, b) => new AST.Number({ value: a * b }),
        '/': (a, b) => new AST.Number({ value: a / b }),
        '=': (a, b) => new AST.Boolean({ value: a === b }),
        '>': (a, b) => new AST.Boolean({ value: a > b }),
        '<': (a, b) => new AST.Boolean({ value: a < b }),
        '>=': (a, b) => new AST.Boolean({ value: a >= b }),
        '<=': (a, b) => new AST.Boolean({ value: a <= b }),
      }
    }
  }

  get(symbol) {
    if (this.data[symbol]) {
      return this.data[symbol]
    }

    throw `Symbol ${symbol} is not bound`
  }

  set(symbol, value) {
    this.data[symbol] = value
  }
}