diff --git a/config.h b/config.h
index 5ae9083..c6fc99c 100644
--- a/config.h
+++ b/config.h
@@ -1,4 +1,6 @@
 #pragma once
 
 #define DEBUG 1
+#define PRINT_DISABLE_PREFIXES 1
+
 #define MAX_TOKEN_STRING_LEN 256
diff --git a/inc/print.h b/inc/print.h
index b8775fa..11ecc85 100644
--- a/inc/print.h
+++ b/inc/print.h
@@ -4,13 +4,23 @@
 #include "config.h"
 
 #if DEBUG == 1
-#define pr_debug(...) std::cout << "[" << __FILE__ << ":" << __LINE__ << " " << __func__ << "] debug: " << __VA_ARGS__ << "\n"
-#define pri_debug(...) std::cout << __VA_ARGS__
-#define prs_debug(...) std::cout << "[" << __FILE__ << ":" << __LINE__ << " " << __func__ << "] debug: " << __VA_ARGS__
+	#if PRINT_DISABLE_PREFIXES == 1
+	#define pr_debug(...) std::cout << "debug: " << __VA_ARGS__ << "\n"
+	#define pri_debug(...) std::cout << __VA_ARGS__
+	#define prs_debug(...) std::cout << "debug: " << __VA_ARGS__
+	#else
+	#define pr_debug(...) std::cout << "[" << __FILE__ << ":" << __LINE__ << " " << __func__ << "] debug: " << __VA_ARGS__ << "\n"
+	#define pri_debug(...) std::cout << __VA_ARGS__
+	#define prs_debug(...) std::cout << "[" << __FILE__ << ":" << __LINE__ << " " << __func__ << "] debug: " << __VA_ARGS__
+	#endif
 #else
 #define pr_debug(...) do {} while (0)
 #define pri_debug(...) do {} while (0)
 #define prs_debug(...) do {} while (0)
 #endif
 
+#if PRINT_DISABLE_PREFIXES == 1
+#define pr_warn(...) std::cout << "warning: " << __VA_ARGS__ << "\n"
+#else
 #define pr_warn(...) std::cout << "[" << __FILE__ << ":" << __LINE__ << " " << __func__ << "] warning: " << __VA_ARGS__ << "\n"
+#endif
diff --git a/inc/syntaxer.hpp b/inc/syntaxer.hpp
index 4d108aa..a40efed 100644
--- a/inc/syntaxer.hpp
+++ b/inc/syntaxer.hpp
@@ -6,12 +6,7 @@
 namespace Syntax
 {
 
-struct SyntaxIssue
-{
-
-};
-
-std::vector<SyntaxIssue> check_syntax(std::vector<Expression::Token>& tv);
+int check_syntax(std::vector<Expression::Token>& tv);
 void apply_corrections(std::vector<Expression::Token>& tv);
 std::vector<Expression::Operation> build_op_vector(const std::vector<Expression::Token>& tv);
 
diff --git a/src/main.cpp b/src/main.cpp
index e31310a..d9ea05d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -9,6 +9,13 @@ int main(int argc, char **argv)
 	}
 
 	std::vector<Expression::Token> tv = Parser::tokenize_input(argv[1]);
+
+	if (Syntax::check_syntax(tv))
+	{
+		return 0;
+	}
+
 	Syntax::apply_corrections(tv);
+
 	std::vector<Expression::Operation> ov = Syntax::build_op_vector(tv);
 }
diff --git a/src/syntaxer.cpp b/src/syntaxer.cpp
index 61c7714..5fcffa0 100644
--- a/src/syntaxer.cpp
+++ b/src/syntaxer.cpp
@@ -1,18 +1,215 @@
-#include "syntaxer.hpp"
-#include "parser.hpp"
 #include "expression.hpp"
-#include <vector>
+#include "parser.hpp"
 #include "print.h"
+#include "syntaxer.hpp"
+#include <stack>
+#include <vector>
 
 namespace Syntax {
 
-#if 0
-std::vector<SyntaxIssue> check_syntax(std::vector<Expression::Token>& tv);
+static void highlight_issue(const std::vector<Expression::Token>& tv, const int location)
 {
+	int start = location - 7 < 0 ? 0 : location - 7;
+	int finish = location + 7 > tv.size() - 1 ? tv.size() - 1 : location + 7;
 
+	std::cout << " >>>  ";
+
+	for (int i = start; i <= finish; i++)
+	{
+		if (i == location)
+		{
+			std::cout << "\033[31m" << *tv[i].to_math_str() << "\033[0m ";
+		}
+		else
+		{
+			std::cout << *tv[i].to_math_str() << " ";
+		}
+	}
+
+	std::cout << "\n";
 }
-#endif
 
+int check_syntax(std::vector<Expression::Token>& tv)
+{
+	int problem_cnt = 0;
+
+	// check token type sequence
+	{
+		for (int i = 0, l = tv.size() - 1, pc; pc = problem_cnt, i < l; i++)
+		{
+			switch (tv[i].t)
+			{
+			case Expression::Token::VAR:
+			case Expression::Token::CONST:
+				switch (tv[i+1].t)
+				{
+				case Expression::Token::OPERATOR:
+					switch (tv[i+1].v.o)
+					{
+					case Expression::Token::OPA:
+						pr_warn("Expected operator at token " << i << ", got opening bracket");
+						problem_cnt++;
+						break;
+					case Expression::Token::CPA:
+						break;
+					default:
+						break;
+					}
+					break;
+				case Expression::Token::VAR:
+					pr_warn("Expected operator at token " << i << ", got variable");
+					problem_cnt++;
+					break;
+				case Expression::Token::CONST:
+					pr_warn("Expected operator at token " << i << ", got constant");
+					problem_cnt++;
+					break;
+				default:
+					pr_warn("Impossible token type, this is a bug!");
+					break;
+				}
+				break;
+			case Expression::Token::OPERATOR:
+				switch (tv[i].v.o)
+				{
+				case Expression::Token::OPA:
+					switch (tv[i+1].t)
+					{
+					case Expression::Token::OPERATOR:
+						switch (tv[i+1].v.o)
+						{
+						case Expression::Token::OPA:
+							break;
+						case Expression::Token::CPA:
+							pr_warn("Expected value at token " << i << ", got closing bracket");
+							problem_cnt++;
+							break;
+						default:
+							pr_warn("Expected value at token " << i << ", got operator");
+							problem_cnt++;
+							break;
+						}
+						break;
+					case Expression::Token::CONST:
+					case Expression::Token::VAR:
+						break;
+					default:
+						pr_warn("Impossible token type, this is a bug!");
+						break;
+					}
+					break;
+				case Expression::Token::CPA:
+					switch (tv[i+1].t)
+					{
+					case Expression::Token::OPERATOR:
+						switch (tv[i+1].v.o)
+						{
+						case Expression::Token::CPA:
+							break;
+						case Expression::Token::OPA:
+							pr_warn("Expected operator at token " << i << ", got opening bracket");
+							problem_cnt++;
+							break;
+						default:
+							break;
+						}
+						break;
+					case Expression::Token::CONST:
+						pr_warn("Expected operator at token " << i << ", got constant");
+						problem_cnt++;
+						break;
+					case Expression::Token::VAR:
+						pr_warn("Expected operator at token " << i << ", got variable");
+						problem_cnt++;
+						break;
+					default:
+						pr_warn("Impossible token type, this is a bug!");
+						break;
+					}
+					break;
+				default:
+					switch (tv[i+1].t)
+					{
+					case Expression::Token::OPERATOR:
+						switch (tv[i+1].v.o)
+						{
+						case Expression::Token::CPA:
+							pr_warn("Expected value at token " << i << ", got closing bracket");
+							problem_cnt++;
+							break;
+						case Expression::Token::OPA:
+							break;
+						default:
+							pr_warn("Expected value at token " << i << ", got operator");
+							problem_cnt++;
+							break;
+						}
+						break;
+					case Expression::Token::CONST:
+						break;
+					case Expression::Token::VAR:
+						break;
+					default:
+						pr_warn("Impossible token type, this is a bug!");
+						break;
+					}
+					break;
+				}
+				break;
+			default:
+				pr_warn("Impossible token type, this is a bug!");
+				break;
+			}
+
+			if (pc != problem_cnt)
+			{
+				highlight_issue(tv, i + 1);
+			}
+		}
+	}
+
+	// check bracket matching
+	{
+		std::stack<int> s;
+
+		for (int i = 0, l = tv.size(); i < l; i++)
+		{
+			if (tv[i].t == Expression::Token::OPERATOR)
+			{
+				switch (tv[i].v.o)
+				{
+				case Expression::Token::OPA:
+					s.push(i);
+					break;
+				case Expression::Token::CPA:
+					if (s.size())
+					{
+						s.pop();
+					}
+					else
+					{
+						pr_warn("Missing opening bracket at token " << i);
+						problem_cnt++;
+						highlight_issue(tv, i);
+					}
+					break;
+				default:
+					break;
+				}
+			}
+		}
+
+		for (int i = 0, l = s.size(); i < l; i++)
+		{
+			problem_cnt++;
+			pr_warn("Opening bracket at token " << s.top() << " expected a closing bracket, but none found");
+			highlight_issue(tv, s.top());
+			s.pop();
+		}
+	}
+
+	return problem_cnt;
+}
 
 // get mop = Math OPerator location (=absolute index in std::vector<Expression::Token>)
 // mapper of 'priority vector index' -> 'token vector index'
@@ -377,6 +574,11 @@ void apply_corrections(std::vector<Expression::Token>& tv)
 	std::vector<int> mp;
 	create_prios_vector(tv, mp);
 
+	if (mp.size() == 0)
+	{
+		return;
+	}
+
 	for (int current_prio_level = mp[get_max_index(mp)]; current_prio_level >= 0; current_prio_level--)
 	{
 		// calculate how many ranges need to be processed at this level