Scala解析SML的相互递归函数

Question

我正在尝试使用令牌在Scala中为SML编写解析器。它几乎按照我希望它的工作方式工作，除了当前解析

的事实

让乐趣f x = r并且乐趣在r end;

而不是

让乐趣f x = r和g y in r end;

如何更改我的代码，使其识别出第二个函数不需要FunToken？

def parseDef:Def = {
  currentToken match {
  case ValToken => {
    eat(ValToken);

    val nme:String = currentToken match {
      case IdToken(x) => {advance; x}
      case _ => error("Expected a name after VAL.")
    }

    eat(EqualToken);      
    VAL(nme,parseExp)
    }

  case FunToken => {

    eat(FunToken);

    val fnme:String = currentToken match {
      case IdToken(x) => {advance; x}
      case _ => error("Expected a name after VAL.")
    }

    val xnme:String = currentToken match {
      case IdToken(x) => {advance; x}
      case _ => error("Expected a name after VAL.")
    }

    def parseAnd:Def = currentToken match {
      case AndToken => {eat(AndToken); FUN(fnme,xnme,parseExp,parseAnd)}
      case _ => NOFUN
    }


    FUN(fnme,xnme,parseExp,parseAnd)
    }
    case _ => error("Expected VAL or FUN.");
  }
}

Answer 1

只需实现正确的语法。而不是

@import "bootstrap-sprockets";
@import "bootstrap";
@import "jquery-ui/all";
@import "font-awesome";
@import "magnific-popup";

html,
body {
  height: 100%;
  width: 100%;
}

body {
  font-family: 'Merriweather', 'Helvetica Neue', Arial, sans-serif;
}

hr {
  border-color: #F05F40;
  border-width: 3px;
  max-width: 50px;
}

hr.light {
  border-color: white;
}

a {
  -webkit-transition: all 0.35s;
  -moz-transition: all 0.35s;
  transition: all 0.35s;
  color: #F05F40;
}

a:hover,
a:focus {
  color: #eb3812;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: 'Open Sans', 'Helvetica Neue', Arial, sans-serif;
}

p {
  font-size: 16px;
  line-height: 1.5;
  margin-bottom: 20px;
}

.bg-primary {
  background-color: #F05F40;
}

.bg-dark {
  background-color: #222222;
  color: white;
}

.text-faded {
  color: rgba(255, 255, 255, 0.7);
}

section {
  padding: 100px 0;
}

aside {
  padding: 50px 0;
}

.no-padding {
  padding: 0;
}

.navbar-default {
  background-color: white;
  border-color: rgba(34, 34, 34, 0.05);
  font-family: 'Open Sans', 'Helvetica Neue', Arial, sans-serif;
  -webkit-transition: all 0.35s;
  -moz-transition: all 0.35s;
  transition: all 0.35s;
}

.navbar-default .navbar-header .navbar-brand {
  color: #F05F40;
  font-family: 'Open Sans', 'Helvetica Neue', Arial, sans-serif;
  font-weight: 700;
  text-transform: uppercase;
}

.navbar-default .navbar-header .navbar-brand:hover,
.navbar-default .navbar-header .navbar-brand:focus {
  color: #eb3812;
}

.navbar-default .navbar-header .navbar-toggle {
  font-weight: 700;
  font-size: 12px;
  color: #222222;
  text-transform: uppercase;
}

.navbar-default .nav > li > a,
.navbar-default .nav > li > a:focus {
  text-transform: uppercase;
  font-weight: 700;
  font-size: 13px;
  color: #222222;
}

.navbar-default .nav > li > a:hover,
.navbar-default .nav > li > a:focus:hover {
  color: #F05F40;
}

.navbar-default .nav > li.active > a,
.navbar-default .nav > li.active > a:focus {
  color: #F05F40 !important;
  background-color: transparent;
}

.navbar-default .nav > li.active > a:hover,
.navbar-default .nav > li.active > a:focus:hover {
  background-color: transparent;
}

@media (min-width: 768px) {

  .navbar-default {
    background-color: transparent;
    border-color: rgba(255, 255, 255, 0.3);
  }

  .navbar-default .navbar-header .navbar-brand {
    color: rgba(255, 255, 255, 0.7);
  }

  .navbar-default .navbar-header .navbar-brand:hover,
  .navbar-default .navbar-header .navbar-brand:focus {
    color: white;
  }

  .navbar-default .nav > li > a,
  .navbar-default .nav > li > a:focus {
    color: rgba(255, 255, 255, 0.7);
  }

  .navbar-default .nav > li > a:hover,
  .navbar-default .nav > li > a:focus:hover {
    color: white;
  }

  .navbar-default.affix {
    background-color: white;
    border-color: rgba(34, 34, 34, 0.05);
  }

  .navbar-default.affix .navbar-header .navbar-brand {
    color: #F05F40;
    font-size: 14px;
  }

  .navbar-default.affix .navbar-header .navbar-brand:hover,
  .navbar-default.affix .navbar-header .navbar-brand:focus {
    color: #eb3812;
  }

  .navbar-default.affix .nav > li > a,
  .navbar-default.affix .nav > li > a:focus {
    color: #222222;
  }

  .navbar-default.affix .nav > li > a:hover,
  .navbar-default.affix .nav > li > a:focus:hover {
    color: #F05F40;
  }

}

header {
  position: relative;
  width: 100%;
  min-height: auto;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  background-size: cover;
  -o-background-size: cover;
  background-position: center;
  background-image: asset-data-url("header.jpg");
  text-align: center;
  color: white;
}

header .header-content {
  position: relative;
  text-align: center;
  padding: 100px 15px 100px;
  width: 100%;
}

header .header-content .header-content-inner h1 {
  font-weight: 700;
  text-transform: uppercase;
  margin-top: 0;
  margin-bottom: 0;
  font-size: 30px;
}

header .header-content .header-content-inner hr {
  margin: 30px auto;
}

header .header-content .header-content-inner p {
  font-weight: 300;
  color: rgba(255, 255, 255, 0.7);
  font-size: 16px;
  margin-bottom: 50px;
}

@media (min-width: 768px) {

  header {
    min-height: 100%;
  }

  header .header-content {
    position: absolute;
    top: 50%;
    -webkit-transform: translateY(-50%);
    -ms-transform: translateY(-50%);
    transform: translateY(-50%);
    padding: 0 50px;
  }

  header .header-content .header-content-inner {
    max-width: 1000px;
    margin-left: auto;
    margin-right: auto;
  }

  header .header-content .header-content-inner h1 {
    font-size: 50px;
  }

  header .header-content .header-content-inner p {
    font-size: 18px;
    max-width: 80%;
    margin-left: auto;
    margin-right: auto;
  }

}

.section-heading {
  margin-top: 0;
}

.service-box {
  max-width: 400px;
  margin: 50px auto 0;
}

@media (min-width: 992px) {

  .service-box {
    margin: 20px auto 0;
  }

}

.service-box p {
  margin-bottom: 0;
}

.portfolio-box {
  position: relative;
  display: block;
  max-width: 650px;
  margin: 0 auto;
}

.portfolio-box .portfolio-box-caption {
  color: white;
  opacity: 0;
  display: block;
  background: rgba(240, 95, 64, 0.9);
  position: absolute;
  bottom: 0;
  text-align: center;
  width: 100%;
  height: 100%;
  -webkit-transition: all 0.35s;
  -moz-transition: all 0.35s;
  transition: all 0.35s;
}

.portfolio-box .portfolio-box-caption .portfolio-box-caption-content {
  width: 100%;
  text-align: center;
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

.portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-category,
.portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-name {
  font-family: 'Open Sans', 'Helvetica Neue', Arial, sans-serif;
  padding: 0 15px;
}

.portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-category {
  text-transform: uppercase;
  font-weight: 600;
  font-size: 14px;
}

.portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-name {
  font-size: 18px;
}

.portfolio-box:hover .portfolio-box-caption {
  opacity: 1;
}

.portfolio-box:focus {
  outline: none;
}

@media (min-width: 768px) {

  .portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-category {
    font-size: 16px;
  }

  .portfolio-box .portfolio-box-caption .portfolio-box-caption-content .project-name {
    font-size: 22px;
  }

}

.call-to-action h2 {
  margin: 0 auto 20px;
}

.text-primary {
  color: #F05F40;
}

.no-gutter > [class*='col-'] {
  padding-right: 0;
  padding-left: 0;
}

.btn-default {
  color: #222222;
  background-color: white;
  border-color: white;
  -webkit-transition: all 0.35s;
  -moz-transition: all 0.35s;
  transition: all 0.35s;
}

.btn-default:hover,
.btn-default:focus,
.btn-default.focus,
.btn-default:active,
.btn-default.active,
.open > .dropdown-toggle.btn-default {
  color: #222222;
  background-color: #f2f2f2;
  border-color: #ededed;
}

.btn-default:active,
.btn-default.active,
.open > .dropdown-toggle.btn-default {
  background-image: none;
}

.btn-default.disabled,
.btn-default[disabled],
fieldset[disabled] .btn-default,
.btn-default.disabled:hover,
.btn-default[disabled]:hover,
fieldset[disabled] .btn-default:hover,
.btn-default.disabled:focus,
.btn-default[disabled]:focus,
fieldset[disabled] .btn-default:focus,
.btn-default.disabled.focus,
.btn-default[disabled].focus,
fieldset[disabled] .btn-default.focus,
.btn-default.disabled:active,
.btn-default[disabled]:active,
fieldset[disabled] .btn-default:active,
.btn-default.disabled.active,
.btn-default[disabled].active,
fieldset[disabled] .btn-default.active {
  background-color: white;
  border-color: white;
}

.btn-default .badge {
  color: white;
  background-color: #222222;
}

.btn-primary {
  color: white;
  background-color: #F05F40;
  border-color: #F05F40;
  -webkit-transition: all 0.35s;
  -moz-transition: all 0.35s;
  transition: all 0.35s;
}

.btn-primary:hover,
.btn-primary:focus,
.btn-primary.focus,
.btn-primary:active,
.btn-primary.active,
.open > .dropdown-toggle.btn-primary {
  color: white;
  background-color: #ee4b28;
  border-color: #ed431f;
}

.btn-primary:active,
.btn-primary.active,
.open > .dropdown-toggle.btn-primary {
  background-image: none;
}

.btn-primary.disabled,
.btn-primary[disabled],
fieldset[disabled] .btn-primary,
.btn-primary.disabled:hover,
.btn-primary[disabled]:hover,
fieldset[disabled] .btn-primary:hover,
.btn-primary.disabled:focus,
.btn-primary[disabled]:focus,
fieldset[disabled] .btn-primary:focus,
.btn-primary.disabled.focus,
.btn-primary[disabled].focus,
fieldset[disabled] .btn-primary.focus,
.btn-primary.disabled:active,
.btn-primary[disabled]:active,
fieldset[disabled] .btn-primary:active,
.btn-primary.disabled.active,
.btn-primary[disabled].active,
fieldset[disabled] .btn-primary.active {
  background-color: #F05F40;
  border-color: #F05F40;
}

.btn-primary .badge {
  color: #F05F40;
  background-color: white;
}

.btn {
  font-family: 'Open Sans', 'Helvetica Neue', Arial, sans-serif;
  border: none;
  border-radius: 300px;
  font-weight: 700;
  text-transform: uppercase;
}

.btn-xl {
  padding: 15px 30px;
}

::-moz-selection {
  color: white;
  text-shadow: none;
  background: #222222;
}

::selection {
  color: white;
  text-shadow: none;
  background: #222222;
}

img::selection {
  color: white;
  background: transparent;
}

img::-moz-selection {
  color: white;
  background: transparent;
}

body {
  webkit-tap-highlight-color: #222222;
}

SML的语法实际上是

def ::= "val" id "=" exp | fun
fun ::= "fun" id id "=" exp ["and" fun]

顺便说一句，我认为解析好玩还有其他问题。 AFAICS，你没有在有趣的情况下解析任何“=”。而且，在“和”之后，你甚至不解析任何标识符，只是函数体。

Answer 2

您可以使用＆＃34; uneat＆＃34;将FunToken注入您的输入流。功能。这不是最优雅的解决方案，但它是需要对当前代码进行最少修改的解决方案。

def parseAnd:Def = currentToken match {
    case AndToken => { eat(AndToken); 
                       uneat(FunToken);
                       FUN(fnme,xnme,parseExp,parseAnd) }
  case _ => NOFUN
}