refactor: implemented labelAndExplain(), combining label and explain, and...

Merge request lab2425_spring/WACC_37!9

Co-authored-by: Barf-Vader <47476490+Barf-Vader@users.noreply.github.com>
Co-authored-by: Guy C <gc1523@ic.ac.uk>

src/main/wacc/lexer.scala

@@ -4,7 +4,36 @@ import parsley.Parsley
 import parsley.character
 import parsley.token.{Basic, Lexer}
 import parsley.token.descriptions.*
+import parsley.token.errors._
 
+val errConfig = new ErrorConfig {
+  override def labelSymbol = Map(
+    "!=" -> Label("binary operator"),
+    "%" -> Label("binary operator"),
+    "&&" -> Label("binary operator"),
+    "*" -> Label("binary operator"),
+    "/" -> Label("binary operator"),
+    "<" -> Label("binary operator"),
+    "<=" -> Label("binary operator"),
+    "==" -> Label("binary operator"),
+    ">" -> Label("binary operator"),
+    ">=" -> Label("binary operator"),
+    "||" -> Label("binary operator"),
+    "!" -> Label("unary operator"),
+    "len" -> Label("unary operator"),
+    "ord" -> Label("unary operator"),
+    "chr" -> Label("unary operator"),
+    "bool" -> Label("valid type"),
+    "char" -> Label("valid type"),
+    "int" -> Label("valid type"),
+    "pair" -> Label("valid type"),
+    "string" -> Label("valid type"),
+    "fst" -> Label("pair extraction"),
+    "snd" -> Label("pair extraction"),
+    "false" -> Label("boolean literal"),
+    "true" -> Label("boolean literal")
+  )
+}
 object lexer {
   private val desc = LexicalDesc.plain.copy(
     nameDesc = NameDesc.plain.copy(
@@ -43,7 +72,7 @@ object lexer {
     )
   )
 
-  private val lexer = Lexer(desc)
+  private val lexer = Lexer(desc, errConfig)
   val ident = lexer.lexeme.names.identifier
   val integer = lexer.lexeme.integer.decimal32[Int]
   val negateCheck = lexer.nonlexeme.symbol("-") ~> character.digit
@@ -51,5 +80,15 @@ object lexer {
   val stringLit = lexer.lexeme.string.ascii
   val implicits = lexer.lexeme.symbol.implicits
 
+  val errTokens = Seq(
+    lexer.nonlexeme.names.identifier.map(v => s"identifier $v"),
+    lexer.nonlexeme.integer.decimal32[Int].map(n => s"integer $n"),
+    lexer.nonlexeme.character.ascii.map(c => s"character literal $c"),
+    lexer.nonlexeme.string.ascii.map(s => s"string literal $s"),
+    character.whitespace.map(_ => "")
+  ) ++ desc.symbolDesc.hardKeywords.map { k =>
+    lexer.nonlexeme.symbol(k).as(s"keyword $k")
+  }
+
   def fully[A](p: Parsley[A]): Parsley[A] = lexer.fully(p)
 }

src/main/wacc/parser.scala

@@ -6,14 +6,51 @@ import parsley.Parsley.{atomic, many, notFollowedBy, pure}
 import parsley.combinator.{countSome, sepBy}
 import parsley.expr.{precedence, SOps, InfixL, InfixN, InfixR, Prefix, Atoms}
 import parsley.errors.combinator._
-import parsley.cats.combinator.{sepBy1, some}
+import parsley.syntax.zipped._
+import parsley.cats.combinator.{some}
 import cats.data.NonEmptyList
+import parsley.errors.DefaultErrorBuilder
+import parsley.errors.ErrorBuilder
+import parsley.errors.tokenextractors.LexToken
 
 object parser {
   import lexer.implicits.implicitSymbol
-  import lexer.{ident, integer, charLit, stringLit, negateCheck}
+  import lexer.{ident, integer, charLit, stringLit, negateCheck, errTokens}
   import ast._
 
+  // error extensions
+  extension [A](p: Parsley[A]) {
+    // combines label and explain together into one function call
+    def labelAndExplain(label: String, explanation: String): Parsley[A] = {
+      p.label(label).explain(explanation)
+    }
+    def labelAndExplain(t: LabelType): Parsley[A] = {
+      t match {
+        case LabelType.Expr =>
+          labelWithType(t).explain(
+            "a valid expression can start with: null, literals, identifiers, unary operators, or parentheses. " +
+              "Expressions can also contain array indexing and binary operators. " +
+              "Pair extraction is not allowed in expressions, only in assignments."
+          )
+        case _ => labelWithType(t)
+      }
+    }
+
+    def labelWithType(t: LabelType): Parsley[A] = {
+      t match {
+        case LabelType.Expr => p.label("valid expression")
+        case LabelType.Pair => p.label("valid pair")
+      }
+    }
+  }
+
+  enum LabelType:
+    case Expr
+    case Pair
+
+  implicit val builder: ErrorBuilder[String] = new DefaultErrorBuilder with LexToken {
+    def tokens = errTokens
+  }
   def parse(input: String): Result[String, Program] = parser.parse(input)
   private val parser = lexer.fully(`<program>`)
 
@@ -28,11 +65,14 @@ object parser {
         Greater from ">",
         GreaterEq from ">="
       ) +:
-      SOps(InfixL)(Add from "+", Sub from "-") +:
+      SOps(InfixL)(
+        (Add from "+").label("binary operator"),
+        (Sub from "-").label("binary operator")
+      ) +:
       SOps(InfixL)(Mul from "*", Div from "/", Mod from "%") +:
       SOps(Prefix)(
         Not from "!",
-        Negate from (notFollowedBy(negateCheck) ~> "-"),
+        (Negate from (notFollowedBy(negateCheck) ~> "-")).hide,
         Len from "len",
         Ord from "ord",
         Chr from "chr"
@@ -42,10 +82,10 @@ object parser {
 
   // Atoms
   private lazy val `<atom>`: Atoms[Expr6] = Atoms(
-    IntLiter(integer),
+    IntLiter(integer).label("integer literal"),
-    BoolLiter(("true" as true) | ("false" as false)),
+    BoolLiter(("true" as true) | ("false" as false)).label("boolean literal"),
-    CharLiter(charLit),
+    CharLiter(charLit).label("character literal"),
-    StrLiter(stringLit),
+    StrLiter(stringLit).label("string literal"),
     PairLiter from "null",
     `<ident-or-array-elem>`,
     Parens("(" ~> `<expr>` <~ ")")
@@ -75,8 +115,10 @@ object parser {
 
   // Statements
   private lazy val `<program>` = Program(
-    "begin" ~> many(atomic(`<type>` <~> `<ident>` <~ "(") <**> `<partial-func-decl>`),
+    "begin" ~> many(
-    `<stmt>` <~ "end"
+      atomic(`<type>`.label("function declaration") <~> `<ident>` <~ "(") <**> `<partial-func-decl>`
+    ).label("function declaration"),
+    `<stmt>`.label("main program body") <~ "end"
   )
   private lazy val `<partial-func-decl>` =
     FuncDecl(
@@ -87,23 +129,28 @@ object parser {
     )
   private lazy val `<param>` = Param(`<type>`, `<ident>`)
   private lazy val `<stmt>`: Parsley[NonEmptyList[Stmt]] =
-    sepBy1(`<basic-stmt>`, ";")
+    (
+      `<basic-stmt>`.label("main program body"),
+      (many(";" ~> `<basic-stmt>`.label("statement after ';'"))) </> Nil
+    ).zipped(NonEmptyList.apply)
+
   private lazy val `<basic-stmt>` =
     (Skip from "skip")
       | Read("read" ~> `<lvalue>`)
-      | Free("free" ~> `<expr>`)
+      | Free("free" ~> `<expr>`.labelAndExplain(LabelType.Expr))
-      | Return("return" ~> `<expr>`)
+      | Return("return" ~> `<expr>`.labelAndExplain(LabelType.Expr))
-      | Exit("exit" ~> `<expr>`)
+      | Exit("exit" ~> `<expr>`.labelAndExplain(LabelType.Expr))
-      | Print("print" ~> `<expr>`, pure(false))
+      | Print("print" ~> `<expr>`.labelAndExplain(LabelType.Expr), pure(false))
-      | Print("println" ~> `<expr>`, pure(true))
+      | Print("println" ~> `<expr>`.labelAndExplain(LabelType.Expr), pure(true))
       | If(
-        "if" ~> `<expr>` <~ "then",
+        "if" ~> `<expr>`.labelWithType(LabelType.Expr) <~ "then",
         `<stmt>` <~ "else",
         `<stmt>` <~ "fi"
       )
-      | While("while" ~> `<expr>` <~ "do", `<stmt>` <~ "done")
+      | While("while" ~> `<expr>`.labelWithType(LabelType.Expr) <~ "do", `<stmt>` <~ "done")
       | Block("begin" ~> `<stmt>` <~ "end")
-      | VarDecl(`<type>`, `<ident>` <~ "=", `<rvalue>`)
+      | VarDecl(`<type>`, `<ident>` <~ "=", `<rvalue>`.label("valid initial value for variable"))
+      // TODO: Can we inline the name of the variable in the message
       | Assign(`<lvalue>` <~ "=", `<rvalue>`)
   private lazy val `<lvalue>`: Parsley[LValue] =
     `<pair-elem>` | `<ident-or-array-elem>`
@@ -117,9 +164,10 @@ object parser {
       Call(
         "call" ~> `<ident>` <~ "(",
         sepBy(`<expr>`, ",") <~ ")"
-      ) | `<expr>`
+      ) | `<expr>`.labelWithType(LabelType.Expr)
   private lazy val `<pair-elem>` =
-    Fst("fst" ~> `<lvalue>`) | Snd("snd" ~> `<lvalue>`)
+    Fst("fst" ~> `<lvalue>`.label("valid pair"))
+      | Snd("snd" ~> `<lvalue>`.label("valid pair"))
   private lazy val `<array-liter>` = ArrayLiter(
     "[" ~> sepBy(`<expr>`, ",") <~ "]"
   )