Merge pull request #90 from krperry/list-negative-fix

Fixed the problem where negative numbers have space between '-' and n…

Author: richpl

README.md

@@ -213,7 +213,7 @@ Program terminated
 ### Statement structure
 
 As per usual in old school BASIC, all program statements must be prefixed with a line number which indicates the order in which the
-statements may be executed. A statement may be modified or
+statements may be executed. There is no renumber command to allow all line numbers to be modified. A statement may be modified or
 replaced by re-entering a statement with the same line number:
 
 ```
@@ -389,6 +389,40 @@ Proper error handling is provided:
 - **OUT OF DATA**: When there are no more DATA items to read
 - Index validation occurs BEFORE consuming DATA items
 
+#### Array Support in READ
+
+The **READ** statement now supports reading data directly into array elements, using expressions for array indices:
+
+```
+> 10 DIM A(5)
+> 20 DIM N$(3)
+> 30 DATA 10, 20, 30, "Hello", "World"
+> 40 READ A(1), A(2), A(3), N$(1), N$(2)
+> 50 PRINT A(1); A(2); A(3); N$(1); N$(2)
+> RUN
+102030HelloWorld
+>
+```
+
+Array indices can be complex expressions including variables and arithmetic:
+
+```
+> 10 DIM B(10)
+> 20 I = 2
+> 30 DATA 100, 200
+> 40 READ B(I*3), B(I+4)
+> 50 PRINT "B(6)="; B(6)  REM Shows 200 (second value overwrites first)
+> RUN
+B(6)=200
+>
+```
+
+Proper error handling is provided:
+- **SUBSCRIPT ERROR**: When array indices are out of bounds or negative
+- **OUT OF DATA**: When there are no more DATA items to read
+- Index validation occurs BEFORE consuming DATA items
+
+
 ### Comments
 
 The **REM** statement is used to indicate a comment, and occupies an entire statement. It has no effect on execution:
@@ -1230,11 +1264,8 @@ a subroutine call, or program termination. This paradigm of using the parser to
 object to make control flow decisions and to track execution, and a signalling mechanism to allow the parser to signal
 control flow changes to the Program object, is used consistently throughout the implementation.
 
-## Open issues
+## Python Basic feature
 
-* It is not possible to renumber a program. This would require considerable extra functionality.
-* Negative values are printed with a space (e.g. '- 5') in program listings because of tokenization. This does not affect functionality.
-* User input values cannot be directly assigned to array variables in an **INPUT** or **READ** statement
 * Strings representing numbers (e.g. "10") can actually be assigned to numeric variables in **INPUT** and **READ** statements without an
 error, Python will silently convert them to integers.
 

program.py

@@ -175,13 +175,31 @@ def str_statement(self, line_number):
         statement = self.__program[line_number]
         if statement[0].category == Token.DATA:
             statement = self.__data.getTokens(line_number)
-        for token in statement:
+        
+        # Track operators and contexts where minus might be unary
+        operators_and_contexts = {
+            Token.PLUS, Token.MINUS, Token.TIMES, Token.DIVIDE, Token.MODULO,
+            Token.ASSIGNOP, Token.EQUAL, Token.NOTEQUAL, Token.GREATER, 
+            Token.LESSER, Token.LESSEQUAL, Token.GREATEQUAL,
+            Token.LEFTPAREN, Token.COMMA, Token.AND, Token.OR
+        }
+        
+        for i, token in enumerate(statement):
             # Add in quotes for strings
             if token.category == Token.STRING:
                 line_text += '"' + token.lexeme + '" '
-
             else:
-                line_text += token.lexeme + " "
+                # Check if this is a minus sign that should be treated as unary
+                if (token.category == Token.MINUS and 
+                    i + 1 < len(statement) and 
+                    statement[i + 1].category in {Token.UNSIGNEDINT, Token.UNSIGNEDFLOAT} and
+                    (i == 0 or statement[i - 1].category in operators_and_contexts)):
+                    # This is a unary minus, don't add space after it
+                    line_text += token.lexeme
+                else:
+                    # Normal token, add space after
+                    line_text += token.lexeme + " "
+        
         line_text += "\n"
         return line_text