From b79949a98935e4fdf923b4392eea275e2ed1c83d Mon Sep 17 00:00:00 2001
From: Robert Spralja <robert.spralja@gmail.com>
Date: Thu, 3 Mar 2022 17:59:34 +0100
Subject: [PATCH 1/2] Implemented SyntaxError

SyntaxError takes three positional arguments `message, tokens, current`

Printing syntax error will print the line that the error occured and the
offending token will be surrounded by '~~'.
---
 src/errors/__init__.py | 42 ++++++++++++++++++++++++++++++++++++++++++
 src/pychart/runner.py  | 28 ++++++++++++++++------------
 2 files changed, 58 insertions(+), 12 deletions(-)
 create mode 100644 src/errors/__init__.py

diff --git a/src/errors/__init__.py b/src/errors/__init__.py
new file mode 100644
index 0000000..7277895
--- /dev/null
+++ b/src/errors/__init__.py
@@ -0,0 +1,42 @@
+
+
+class BaseError(Exception):
+    def __init__(self, message):
+        super().__init__(message)
+
+    @property
+    def traceback(self):
+        return self._traceback
+
+
+class SyntaxError(BaseError):
+    def __init__(self, message, tokens, current):
+        self.tokens = tokens
+        self.current = current
+        super().__init__(message)
+    
+    def __str__(self):
+        string = ''
+        current_token = self.tokens[self.current]
+        current_line = current_token.line
+
+        start_of_line = self.current
+        while self.tokens[start_of_line].line == current_line:
+            start_of_line -= 1
+
+        start_of_line += 1
+
+        end_of_line = self.current
+        while self.tokens[end_of_line].line == current_line:
+            end_of_line += 1
+
+
+        for token in self.tokens[start_of_line:end_of_line]:
+            if token == current_token:
+                string += '~~'
+            string += token.lexem + ' '
+
+            if token == current_token:
+                string += '~~'
+
+        return string
diff --git a/src/pychart/runner.py b/src/pychart/runner.py
index 89e990d..1e85ccd 100644
--- a/src/pychart/runner.py
+++ b/src/pychart/runner.py
@@ -1,24 +1,28 @@
 from src.scanner import Scanner
 from src.pyparser import Parser
+from src import errors
 
 
 def run(source: str):
-    scanner = Scanner(source)
-    tokens = scanner.get_tokens()
-    ast = Parser(tokens).parse()
+    try:
+        scanner = Scanner(source)
+        tokens = scanner.get_tokens()
+        ast = Parser(tokens).parse()
 
-    if ast is None:
-        return
+        if ast is None:
+            return
 
-    value = ast()
+        value = ast()
 
-    try:
-        value = int(value)
-    except:
-        pass
+        try:
+            value = int(value)
+        except:
+            pass
 
-    # print(f"AST: {ast}")
-    print(value)
+        # print(f"AST: {ast}")
+        print(value)
+    except errors.BaseError as e:
+        print(e)
 
 
 def run_prompt():

From 7783ab3239ae6e4349bdb44728bd6c9c15ef6ecf Mon Sep 17 00:00:00 2001
From: Robert Spralja <robert.spralja@gmail.com>
Date: Thu, 3 Mar 2022 18:10:16 +0100
Subject: [PATCH 2/2] fixed errors in SyntaxError.__str__

---
 src/errors/__init__.py | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/src/errors/__init__.py b/src/errors/__init__.py
index 7277895..13a1f1a 100644
--- a/src/errors/__init__.py
+++ b/src/errors/__init__.py
@@ -21,22 +21,20 @@ def __str__(self):
         current_line = current_token.line
 
         start_of_line = self.current
-        while self.tokens[start_of_line].line == current_line:
+        while start_of_line > 0 and self.tokens[start_of_line].line == current_line:
             start_of_line -= 1
 
-        start_of_line += 1
-
         end_of_line = self.current
-        while self.tokens[end_of_line].line == current_line:
+        while end_of_line < len(self.tokens) and self.tokens[end_of_line].line == current_line:
             end_of_line += 1
 
 
-        for token in self.tokens[start_of_line:end_of_line]:
-            if token == current_token:
-                string += '~~'
-            string += token.lexem + ' '
+        for token, index in zip(self.tokens[start_of_line:end_of_line], range(start_of_line, end_of_line)):
+            if index == self.current:
+                string += '~~ '
+            string += token.lexeme + ' '
 
-            if token == current_token:
+            if index == self.current:
                 string += '~~'
 
         return string