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.value + b.value }),
        '-': (a, b) => new AST.Number({ value: a.value - b.value }),
        '*': (a, b) => new AST.Number({ value: a.value * b.value }),
        '/': (a, b) => new AST.Number({ value: a.value / b.value }),
        '=': (a, b) => new AST.Boolean({ value: a.value === b.value }),
        '>': (a, b) => new AST.Boolean({ value: a.value > b.value }),
        '<': (a, b) => new AST.Boolean({ value: a.value < b.value }),
        '>=': (a, b) => new AST.Boolean({ value: a.value >= b.value }),
        '<=': (a, b) => new AST.Boolean({ value: a.value <= b.value }),
      }
    }
  }

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

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

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