Cleanup parser and extract common logic.

src/main/kotlin/gay/pizza/pork/frontend/FileFrontend.kt

@@ -1,6 +1,5 @@
 package gay.pizza.pork.frontend
 
-import gay.pizza.pork.ast.NodeVisitor
 import gay.pizza.pork.parse.CharSource
 import gay.pizza.pork.parse.StringCharSource
 import java.nio.file.Path

src/main/kotlin/gay/pizza/pork/parse/Parser.kt

@@ -6,75 +6,106 @@ import gay.pizza.pork.util.StringEscape
 class Parser(source: PeekableSource<Token>) {
   private val unsanitizedSource = source
 
-  private fun readIntLiteral(): IntLiteral {
-    val token = expect(TokenType.IntLiteral)
-    return IntLiteral(token.text.toInt())
+  private fun readIntLiteral(): IntLiteral =
+    expect(TokenType.IntLiteral) { IntLiteral(it.text.toInt()) }
+
+  private fun readStringLiteral(): StringLiteral =
+    expect(TokenType.StringLiteral) {
+      val content = StringEscape.unescape(StringEscape.unquote(it.text))
+      StringLiteral(content)
+    }
+
+  private fun readBooleanLiteral(): BooleanLiteral =
+    expect(TokenType.True, TokenType.False) {
+      BooleanLiteral(it.type == TokenType.True)
+    }
+
+  private fun readListLiteral(): ListLiteral {
+    expect(TokenType.LeftBracket)
+    val items = collect(TokenType.RightBracket, TokenType.Comma) {
+      readExpression()
+    }
+    expect(TokenType.RightBracket)
+    return ListLiteral(items)
   }
 
-  private fun readSymbol(): Symbol {
-    val token = expect(TokenType.Symbol)
-    return Symbol(token.text)
+  private fun readSymbol(): Symbol =
+    expect(TokenType.Symbol) { Symbol(it.text) }
+
+  private fun readSymbolCases(): Expression {
+    val symbol = readSymbol()
+    return if (next(TokenType.LeftParentheses)) {
+      val arguments = collect(TokenType.RightParentheses, TokenType.Comma) {
+        readExpression()
+      }
+      expect(TokenType.RightParentheses)
+      FunctionCall(symbol, arguments)
+    } else if (next(TokenType.Equals)) {
+      Define(symbol, readExpression())
+    } else {
+      SymbolReference(symbol)
+    }
   }
 
+  private fun readLambda(): Lambda {
+    expect(TokenType.LeftCurly)
+    val arguments = mutableListOf<Symbol>()
+    while (!peek(TokenType.In)) {
+      val symbol = readSymbol()
+      arguments.add(symbol)
+      if (next(TokenType.Comma)) {
+        continue
+      } else {
+        break
+      }
+    }
+    expect(TokenType.In)
+    val items = collect(TokenType.RightCurly) {
+      readExpression()
+    }
+    expect(TokenType.RightCurly)
+    return Lambda(arguments, items)
+  }
+
+  private fun readParentheses(): Parentheses {
+    expect(TokenType.LeftParentheses)
+    val expression = readExpression()
+    expect(TokenType.RightParentheses)
+    return Parentheses(expression)
+  }
+
+  private fun readNegation(): PrefixOperation =
+    expect(TokenType.Negation) {
+      PrefixOperation(PrefixOperator.Negate, readExpression())
+    }
+
   private fun readIf(): If {
     expect(TokenType.If)
     val condition = readExpression()
     expect(TokenType.Then)
     val thenExpression = readExpression()
     var elseExpression: Expression? = null
-    if (peekType(TokenType.Else)) {
-      expect(TokenType.Else)
+    if (next(TokenType.Else)) {
       elseExpression = readExpression()
     }
     return If(condition, thenExpression, elseExpression)
   }
 
-  private fun readSymbolCases(): Expression {
-    val symbol = readSymbol()
-    return if (peekType(TokenType.LeftParentheses)) {
-      expect(TokenType.LeftParentheses)
-      val arguments = collectExpressions(TokenType.RightParentheses, TokenType.Comma)
-      expect(TokenType.RightParentheses)
-      FunctionCall(symbol, arguments)
-    } else if (peekType(TokenType.Equals)) {
-      expect(TokenType.Equals)
-      Define(symbol, readExpression())
-    } else {
-      SymbolReference(symbol)
-    }
-  }
-
-  fun readLambda(): Lambda {
-    expect(TokenType.LeftCurly)
-    val arguments = mutableListOf<Symbol>()
-    while (!peekType(TokenType.In)) {
-      val symbol = readSymbol()
-      arguments.add(symbol)
-      if (peekType(TokenType.Comma)) {
-        expect(TokenType.Comma)
-        continue
-      } else {
-        break
-      }
-    }
-    expect(TokenType.In)
-    val items = collectExpressions(TokenType.RightCurly)
-    expect(TokenType.RightCurly)
-    return Lambda(arguments, items)
-  }
-
   fun readExpression(): Expression {
     val token = peek()
     val expression = when (token.type) {
-      TokenType.StringLiteral -> {
-        expect(TokenType.StringLiteral)
-        return StringLiteral(StringEscape.unescape(StringEscape.unquote(token.text)))
-      }
-
       TokenType.IntLiteral -> {
         readIntLiteral()
       }
 
+      TokenType.StringLiteral -> {
+        readStringLiteral()
+      }
+
+      TokenType.True, TokenType.False -> {
+        readBooleanLiteral()
+      }
+
       TokenType.LeftBracket -> {
         readListLiteral()
       }
@@ -88,39 +119,25 @@ class Parser(source: PeekableSource<Token>) {
       }
 
       TokenType.LeftParentheses -> {
-        expect(TokenType.LeftParentheses)
-        val expression = readExpression()
-        expect(TokenType.RightParentheses)
-        Parentheses(expression)
-      }
-
-      TokenType.True -> {
-        expect(TokenType.True)
-        return BooleanLiteral(true)
-      }
-
-      TokenType.False -> {
-        expect(TokenType.False)
-        return BooleanLiteral(false)
+        readParentheses()
       }
 
       TokenType.Negation -> {
-        expect(TokenType.Negation)
-        return PrefixOperation(PrefixOperator.Negate, readExpression())
+        readNegation()
       }
 
       TokenType.If -> {
-        return readIf()
+        readIf()
       }
 
       else -> {
         throw RuntimeException(
-          "Failed to parse token: ${token.type} '${token.text}' as expression" +
-          " (index ${unsanitizedSource.currentIndex})")
+          "Failed to parse token: ${token.type} '${token.text}' as" +
+          " expression (index ${unsanitizedSource.currentIndex})")
       }
     }
 
-    if (peekType(
+    if (peek(
         TokenType.Plus,
         TokenType.Minus,
         TokenType.Multiply,
@@ -146,44 +163,52 @@ class Parser(source: PeekableSource<Token>) {
       else -> throw RuntimeException("Unknown Infix Operator")
     }
 
-  fun readListLiteral(): ListLiteral {
-    expect(TokenType.LeftBracket)
-    val items = collectExpressions(TokenType.RightBracket, TokenType.Comma)
-    expect(TokenType.RightBracket)
-    return ListLiteral(items)
-  }
-
   fun readProgram(): Program {
-    val items = collectExpressions(TokenType.EndOfFile)
+    val items = collect(TokenType.EndOfFile) { readExpression() }
     expect(TokenType.EndOfFile)
     return Program(items)
   }
 
-  private fun collectExpressions(peeking: TokenType, consuming: TokenType? = null): List<Expression> {
-    val items = mutableListOf<Expression>()
-    while (!peekType(peeking)) {
-      val expression = readExpression()
-      if (consuming != null && !peekType(peeking)) {
-        expect(consuming)
+  private fun <T> collect(
+    peeking: TokenType,
+    consuming: TokenType? = null,
+    read: () -> T
+  ): List<T> {
+    val items = mutableListOf<T>()
+    while (!peek(peeking)) {
+      val expression = read()
+      if (consuming != null) {
+        next(consuming)
       }
       items.add(expression)
     }
     return items
   }
 
-  private fun peekType(vararg types: TokenType): Boolean {
+  private fun peek(vararg types: TokenType): Boolean {
     val token = peek()
     return types.contains(token.type)
   }
 
-  private fun expect(type: TokenType): Token {
+  private fun next(type: TokenType): Boolean {
+    return if (peek(type)) {
+      expect(type)
+      true
+    } else false
+  }
+
+  private fun expect(vararg types: TokenType): Token {
     val token = next()
-    if (token.type != type) {
-      throw RuntimeException("Expected token type '${type}' but got type ${token.type} '${token.text}'")
+    if (!types.contains(token.type)) {
+      throw RuntimeException("Expected one of ${types.joinToString(", ")} " +
+        " but got type ${token.type} '${token.text}'")
     }
     return token
   }
 
+  private fun <T> expect(vararg types: TokenType, consume: (Token) -> T): T =
+    consume(expect(*types))
+
   private fun next(): Token {
     while (true) {
       val token = unsanitizedSource.next()