From 1ef6f0e6b9083748e5b91743f15f10f09c6b8432 Mon Sep 17 00:00:00 2001
From: Elias Haugsbakk <elias.haugsbakk@gmail.com>
Date: Fri, 18 Sep 2026 23:10:31 +0200
Subject: Implement parser creating AST

---
 .../java/no/eliashaugsbakk/kompilator/Main.java    | 17 +++++
 .../no/eliashaugsbakk/kompilator/parsing/AST.java  |  7 ++
 .../eliashaugsbakk/kompilator/parsing/Parser.java  | 79 ++++++++++++++++++++++
 .../kompilator/parsing/ParserException.java        |  7 ++
 .../kompilator/parsing/node/ASTNode.java           |  7 ++
 .../kompilator/parsing/node/Program.java           | 16 +++++
 .../parsing/node/expression/Expression.java        | 17 +++++
 .../parsing/node/expression/FunctionCall.java      | 16 +++++
 .../parsing/node/expression/StringLiteral.java     | 12 ++++
 .../node/statement/ExpressionStatement.java        | 10 +++
 .../parsing/node/statement/Statement.java          | 15 ++++
 .../kompilator/tokenization/Lexer.java             |  2 +-
 .../kompilator/tokenization/Token.java             | 13 +---
 .../kompilator/tokenization/TokenType.java         |  2 +-
 .../kompilator/parsing/ParserTest.java             | 70 +++++++++++++++++++
 .../kompilator/tokenization/LexerTest.java         | 18 ++---
 16 files changed, 285 insertions(+), 23 deletions(-)
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/ParserException.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/ASTNode.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/Program.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/Expression.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/FunctionCall.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/StringLiteral.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/ExpressionStatement.java
 create mode 100644 src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/Statement.java
 create mode 100644 src/test/java/no/eliashaugsbakk/kompilator/parsing/ParserTest.java

diff --git a/src/main/java/no/eliashaugsbakk/kompilator/Main.java b/src/main/java/no/eliashaugsbakk/kompilator/Main.java
index aad3753..fa7f79c 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/Main.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/Main.java
@@ -6,6 +6,11 @@ import no.eliashaugsbakk.kompilator.IO.FileReaderWriter;
 import no.eliashaugsbakk.kompilator.IO.FileReaderWriterException;
 import no.eliashaugsbakk.kompilator.asmGeneration.AssemblyBuilder;
 import no.eliashaugsbakk.kompilator.assembleAndLink.AssemblerAndLinker;
+import no.eliashaugsbakk.kompilator.parsing.AST;
+import no.eliashaugsbakk.kompilator.parsing.Parser;
+import no.eliashaugsbakk.kompilator.parsing.ParserException;
+import no.eliashaugsbakk.kompilator.tokenization.Lexer;
+import no.eliashaugsbakk.kompilator.tokenization.Token;
 
 public class Main {
   public static final String programFileExtension = "spå";
@@ -33,6 +38,18 @@ public class Main {
       System.exit(1);
     }
 
+    List<Token> tokens = new Lexer(inputProgram.fileBody()).tokenize();
+    AST ast = null;
+    try {
+      ast = new Parser(tokens).parse();
+    } catch (ParserException e) {
+      IO.println("Error while parsing: " + e.getMessage());
+    }
+
+    // TODO:
+    // new Analyzer(ast).analyze();
+    // List<String> IR = new IRGenerator(ast).generate();
+
     List<String> IR = List.of();
 
     String assembly = new AssemblyBuilder().createAssembly(IR);
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/AST.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/AST.java
index 3f54e3c..95ec77c 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/parsing/AST.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/AST.java
@@ -1,4 +1,11 @@
 package no.eliashaugsbakk.kompilator.parsing;
 
+import no.eliashaugsbakk.kompilator.parsing.node.ASTNode;
+
 public class AST {
+  ASTNode root;
+
+  AST(ASTNode root) {
+    this.root = root;
+  }
 }
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/Parser.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/Parser.java
index a41a1bf..53af71c 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/parsing/Parser.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/Parser.java
@@ -1,4 +1,83 @@
 package no.eliashaugsbakk.kompilator.parsing;
 
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.EOF;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.KEYWORD;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.LPAREN;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.RPAREN;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.SEMICOLON;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.STRING;
+
+import java.util.ArrayList;
+import java.util.List;
+import no.eliashaugsbakk.kompilator.parsing.node.Program;
+import no.eliashaugsbakk.kompilator.parsing.node.expression.Expression;
+import no.eliashaugsbakk.kompilator.parsing.node.expression.FunctionCall;
+import no.eliashaugsbakk.kompilator.parsing.node.expression.StringLiteral;
+import no.eliashaugsbakk.kompilator.parsing.node.statement.ExpressionStatement;
+import no.eliashaugsbakk.kompilator.tokenization.Token;
+
 public class Parser {
+  private final List<Token> tokens;
+  private int position = 0;
+
+  public Parser(List<Token> tokens) {
+    this.tokens = tokens;
+  }
+
+  public AST parse() throws ParserException {
+    Program rootNode = new Program();
+
+    while (position < tokens.size()) {
+      Token token = tokens.get(position);
+
+      if (token.type() == KEYWORD) {
+        String functionName = token.value();
+        position++;
+
+        List<Expression> arguments = parseArguments();
+
+        FunctionCall functionCall = new FunctionCall(functionName, arguments);
+        rootNode.addStatement(new ExpressionStatement(functionCall));
+      } else if (token.type() == EOF) {
+        break;
+      } else {
+        IO.println("Unknown token: " + token.value() + ". Skipping...");
+        position++;
+      }
+    }
+
+    return new AST(rootNode);
+  }
+
+  List<Expression> parseArguments() throws ParserException {
+    List<Expression> arguments = new ArrayList<>();
+
+    if (position >= tokens.size() || tokens.get(position).type() != LPAREN) {
+      throw new ParserException(tokens.get(position).line(), tokens.get(position).colum(),
+          "Unexpected token:" + tokens.get(position).value() + "\n Expected: (");
+    }
+    position++;
+
+    while (position < tokens.size() && tokens.get(position).type() != RPAREN) {
+      if (tokens.get(position).type() == STRING) {
+        arguments.add(new StringLiteral(tokens.get(position).value()));
+      }
+      position++;
+    }
+
+    if (position >= tokens.size()) {
+      throw new ParserException(-1, -1, "Unexpected end of file, expected )");
+    }
+    position++;
+
+    if (position >= tokens.size() || tokens.get(position).type() != SEMICOLON) {
+      throw new ParserException(position < tokens.size() ? tokens.get(position).line() : -1,
+          position < tokens.size() ? tokens.get(position).colum() : -1,
+          "Unexpected token: " + (position < tokens.size() ? tokens.get(position).value() : "EOF") +
+              "\n" + "Expected: ;");
+    }
+    position++;
+
+    return arguments;
+  }
 }
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/ParserException.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/ParserException.java
new file mode 100644
index 0000000..ac96a5c
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/ParserException.java
@@ -0,0 +1,7 @@
+package no.eliashaugsbakk.kompilator.parsing;
+
+public class ParserException extends Exception {
+  public ParserException(int line, int column, String message) {
+    super(line + ":" + column + ", " + message);
+  }
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/ASTNode.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/ASTNode.java
new file mode 100644
index 0000000..1eb201c
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/ASTNode.java
@@ -0,0 +1,7 @@
+package no.eliashaugsbakk.kompilator.parsing.node;
+
+/**
+ * Base class for all nodes in the Abstract Syntax Tree.
+ */
+public abstract class ASTNode {
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/Program.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/Program.java
new file mode 100644
index 0000000..0c7cd32
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/Program.java
@@ -0,0 +1,16 @@
+package no.eliashaugsbakk.kompilator.parsing.node;
+
+import java.util.ArrayList;
+import java.util.List;
+import no.eliashaugsbakk.kompilator.parsing.node.statement.Statement;
+
+/**
+ * Root node of the AST. Contains all top-level statements.
+ */
+public class Program extends ASTNode {
+  public List<Statement> statements = new ArrayList<>();
+
+  public void addStatement(Statement statement) {
+    this.statements.add(statement);
+  }
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/Expression.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/Expression.java
new file mode 100644
index 0000000..6ca58b2
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/Expression.java
@@ -0,0 +1,17 @@
+package no.eliashaugsbakk.kompilator.parsing.node.expression;
+
+import no.eliashaugsbakk.kompilator.parsing.node.ASTNode;
+
+/**
+ * Base class for all expression nodes.
+ * An expression is a piece of code that evaluates to a value.
+ * Expressions cannot stand alone as statements; they must be used within statements.
+ * <p>
+ * Examples:
+ * - "Hello"          (string literal expression)
+ * - 42               (number literal expression)
+ * - x + 5            (binary operation expression)
+ * - myFunction()     (function call expression)
+ */
+public abstract class Expression extends ASTNode {
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/FunctionCall.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/FunctionCall.java
new file mode 100644
index 0000000..3c46ec4
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/FunctionCall.java
@@ -0,0 +1,16 @@
+package no.eliashaugsbakk.kompilator.parsing.node.expression;
+
+import java.util.List;
+
+/**
+ * Represents a function call statement (e.g., print("Hello, world")).
+ */
+public class FunctionCall extends Expression {
+  public String functionName;
+  public List<Expression> arguments;
+
+  public FunctionCall(String functionName, List<Expression> arguments) {
+    this.functionName = functionName;
+    this.arguments = arguments;
+  }
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/StringLiteral.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/StringLiteral.java
new file mode 100644
index 0000000..67ce405
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/expression/StringLiteral.java
@@ -0,0 +1,12 @@
+package no.eliashaugsbakk.kompilator.parsing.node.expression;
+
+/**
+ * Represents a string literal expression (e.g., "Hello, World").
+ */
+public class StringLiteral extends Expression {
+  public final String value;
+
+  public StringLiteral(String value) {
+    this.value = value;
+  }
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/ExpressionStatement.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/ExpressionStatement.java
new file mode 100644
index 0000000..64bc0a8
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/ExpressionStatement.java
@@ -0,0 +1,10 @@
+package no.eliashaugsbakk.kompilator.parsing.node.statement;
+
+import no.eliashaugsbakk.kompilator.parsing.node.expression.Expression;
+
+public class ExpressionStatement extends Statement {
+  public Expression expression;
+  public ExpressionStatement(Expression expression) {
+    this.expression = expression;
+  }
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/Statement.java b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/Statement.java
new file mode 100644
index 0000000..fc52f9a
--- /dev/null
+++ b/src/main/java/no/eliashaugsbakk/kompilator/parsing/node/statement/Statement.java
@@ -0,0 +1,15 @@
+package no.eliashaugsbakk.kompilator.parsing.node.statement;
+
+import no.eliashaugsbakk.kompilator.parsing.node.ASTNode;
+
+/**
+ * Base class for all statement nodes.
+ * A statement is a top-level line of code that performs an action.
+ * <p>
+ * Examples:
+ * - print("Hello");  (function call statement)
+ * - var x: int = 5;  (variable declaration statement)
+ * - if (x > 0) { }   (conditional statement)
+ */
+public abstract class Statement extends ASTNode {
+}
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Lexer.java b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Lexer.java
index 4149b4f..62d2359 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Lexer.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Lexer.java
@@ -30,7 +30,7 @@ public class Lexer {
     this.input = input;
   }
 
-  List<Token> tokenize() {
+  public List<Token> tokenize() {
 
     while (position < input.length()) {
       char current = input.charAt(position);
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Token.java b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Token.java
index 519b6b6..09c5d83 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Token.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/Token.java
@@ -1,15 +1,4 @@
 package no.eliashaugsbakk.kompilator.tokenization;
 
-class Token {
-  TokenType type;
-  String value;
-  int line;
-  int colum;
-
-  Token(TokenType type, String value, int line, int colum) {
-    this.type = type;
-    this.value = value;
-    this.line = line;
-    this.colum = colum;
-  }
+public record Token(TokenType type, String value, int line, int colum) {
 }
diff --git a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/TokenType.java b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/TokenType.java
index 408abb2..696b46c 100644
--- a/src/main/java/no/eliashaugsbakk/kompilator/tokenization/TokenType.java
+++ b/src/main/java/no/eliashaugsbakk/kompilator/tokenization/TokenType.java
@@ -1,6 +1,6 @@
 package no.eliashaugsbakk.kompilator.tokenization;
 
-enum TokenType {
+public enum TokenType {
   KEYWORD,      // print, var, if, while, function, etc.
   IDENTIFIER,   // variable_1
   STRING,       // "Hello, World!"
diff --git a/src/test/java/no/eliashaugsbakk/kompilator/parsing/ParserTest.java b/src/test/java/no/eliashaugsbakk/kompilator/parsing/ParserTest.java
new file mode 100644
index 0000000..133e9a6
--- /dev/null
+++ b/src/test/java/no/eliashaugsbakk/kompilator/parsing/ParserTest.java
@@ -0,0 +1,70 @@
+package no.eliashaugsbakk.kompilator.parsing;
+
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.KEYWORD;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.LPAREN;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.RPAREN;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.SEMICOLON;
+import static no.eliashaugsbakk.kompilator.tokenization.TokenType.STRING;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.List;
+import no.eliashaugsbakk.kompilator.parsing.node.Program;
+import no.eliashaugsbakk.kompilator.parsing.node.expression.FunctionCall;
+import no.eliashaugsbakk.kompilator.parsing.node.expression.StringLiteral;
+import no.eliashaugsbakk.kompilator.parsing.node.statement.ExpressionStatement;
+import no.eliashaugsbakk.kompilator.tokenization.Token;
+import org.junit.jupiter.api.Test;
+
+class ParserTest {
+
+  @Test
+  void validSyntaxBuildsCorrectTree() throws ParserException {
+    List<Token> tokens = List.of(
+        new Token(KEYWORD, "print", 1, 0),
+        new Token(LPAREN, "(", 1, 5),
+        new Token(STRING, "Hello", 1, 6),
+        new Token(RPAREN, ")", 1, 13),
+        new Token(SEMICOLON, ";", 1, 14)
+    );
+
+    AST ast = new Parser(tokens).parse();
+
+    // Verify tree structure
+    assertNotNull(ast.root);
+    assertInstanceOf(Program.class, ast.root);
+    Program program = (Program) ast.root;
+    assertEquals(1, program.statements.size());
+
+    ExpressionStatement stmt = (ExpressionStatement) program.statements.getFirst();
+    assertInstanceOf(FunctionCall.class, stmt.expression);
+
+    FunctionCall call = (FunctionCall) stmt.expression;
+    assertEquals("print", call.functionName);
+    assertEquals(1, call.arguments.size());
+    assertEquals("Hello", ((StringLiteral) call.arguments.getFirst()).value);
+  }
+
+  @Test
+  void missingSemicolonThrows() {
+    List<Token> tokens = List.of(
+        new Token(KEYWORD, "print", 1, 0),
+        new Token(LPAREN, "(", 1, 5),
+        new Token(STRING, "Hello", 1, 6),
+        new Token(RPAREN, ")", 1, 13)
+    );
+
+    assertThrows(ParserException.class, () -> new Parser(tokens).parse());
+  }
+
+  @Test
+  void missingParenthesisThrows() {
+    List<Token> tokens = List.of(
+        new Token(KEYWORD, "print", 1, 0),
+        new Token(STRING, "Hello", 1, 5),
+        new Token(RPAREN, ")", 1, 12),
+        new Token(SEMICOLON, ";", 1, 13)
+    );
+
+    assertThrows(ParserException.class, () -> new Parser(tokens).parse());
+  }
+}
diff --git a/src/test/java/no/eliashaugsbakk/kompilator/tokenization/LexerTest.java b/src/test/java/no/eliashaugsbakk/kompilator/tokenization/LexerTest.java
index d1fedb9..7f4a5b3 100644
--- a/src/test/java/no/eliashaugsbakk/kompilator/tokenization/LexerTest.java
+++ b/src/test/java/no/eliashaugsbakk/kompilator/tokenization/LexerTest.java
@@ -24,17 +24,17 @@ class LexerTest {
 
     // tokens.forEach(t-> IO.println(t.type + " : " + t.value));
 
-    assertSame(KEYWORD, tokens.getFirst().type);
-    assertEquals(1, tokens.get(0).line);
-    assertEquals(1, tokens.get(0).colum);
+    assertSame(KEYWORD, tokens.getFirst().type());
+    assertEquals(1, tokens.get(0).line());
+    assertEquals(1, tokens.get(0).colum());
 
-    assertSame(LPAREN, tokens.get(1).type);
+    assertSame(LPAREN, tokens.get(1).type());
 
-    assertSame(STRING, tokens.get(2).type);
-    assertTrue(tokens.get(2).value.contains("Hello, World"));
+    assertSame(STRING, tokens.get(2).type());
+    assertTrue(tokens.get(2).value().contains("Hello, World"));
 
-    assertSame(RPAREN, tokens.get(3).type);
-    assertSame(SEMICOLON, tokens.get(4).type);
-    assertSame(EOF, tokens.get(5).type);
+    assertSame(RPAREN, tokens.get(3).type());
+    assertSame(SEMICOLON, tokens.get(4).type());
+    assertSame(EOF, tokens.get(5).type());
   }
 }
-- 
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