sexp-template/src/compiler.js

const AST = require('./ast')
const Env = require('./env')

module.exports = class Compiler {
  constructor(env = null) {
    this.result = ''

    if (env) {
      this.env = env
    } else {
      this.env = new Env()
    }
  }

  compile(tree) {
    tree.forEach(node => {
      this.result += this.compileNode(node)
    })

    return this.result
  }

  compileNode(node) {
    switch (node.constructor) {
      case AST.Number:
      case AST.String:
        return node.value
      case AST.Boolean:
        return node.value === true ? '#t' : '#f'
      case AST.Identifier:
        return this.compileNode(this.env.get(node.name))
      case AST.Conditional:
        let condition = this.compileNode(node.condition)

        if (condition) {
          return this.compileNode(node.ifCase)
        } else {
          return this.compileNode(node.elseCase)
        }
      case AST.Application:
        if (node.function.constructor === AST.Identifier) {
          let f = this.env.get(node.function.name)
          return this.compileNode(f(...node.args.map(arg => this.compileNode(arg))))
        } else if (node.function.constructor === AST.Lambda) {
          let env = new Env(this.env)
          node.function.parameters.forEach((param, index) => {
            env.set(param.name, node.args[index])
          })

          let compiler = new Compiler(env)
          return compiler.compileNode(node.function.body)
        }

        return ''
    }
  }
}