Difference between revisions of "S2 Guide: Troubleshooting"

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 +
== Syntax checklist ==
 +
 +
* Are you ending all statements with a semicolon (;)?
 +
* Have you declared all variables you are using?
 +
* Are you using <tt>$</tt> when you're accessing variables?
 +
* Do your function calls have matching parentheses?
 +
* Do your code blocks have matching brackets?
 +
 
== Deciphering compile errors ==
 
== Deciphering compile errors ==
 +
 +
The layer editor won't let you save a layer that contains compiler errors.  Let's say that in the [[S2 Cookbook: A Testbed Layout]], I test some code that has syntax errors where it says "# Code you want to test goes here".  Here are some example situations of the kinds of compile errors I can encounter, and their solution.
 +
 +
=== Forgetting to declare a variable ===
 +
 +
Let's make a really easy error first, to get through the basics.  Here's an example where I forget to declare the <tt>$test</tt> variable before I use it:
 +
 +
<syntaxhighlight lang="s2">
 +
    var int length = $test->length();
 +
</syntaxhighlight>
 +
 +
When I try to save and compile, this is the compiler error I get:
 +
 +
  S2 Compiler Output at Thu Jun 17 10:23:17 2010
 +
Error compiling layer:
 +
 +
Compile error: line 15, column 22: Unknown local variable $test
 +
  S2::NodeVarRef, S2/NodeVarRef.pm, 180
 +
  S2::NodeVarRef, S2/NodeVarRef.pm, 151
 +
  S2::NodeTerm, S2/NodeTerm.pm, 182
 +
  S2::NodeTerm, S2/NodeTerm.pm, 66
 +
  S2::NodeExpr, S2/NodeExpr.pm, 46
 +
  S2::NodeVarDeclStmt, S2/NodeVarDeclStmt.pm, 54
 +
  S2::NodeStmtBlock, S2/NodeStmtBlock.pm, 108
 +
  S2::NodeFunction, S2/NodeFunction.pm, 230
 +
  S2::Checker, S2/Checker.pm, 374
 +
  S2::Compiler, S2/Compiler.pm, 34
 +
 
 +
 +
Context
 +
 +
  11:    """</head>""";
 +
  12:    """<body>""";
 +
  13:
 +
  14:
 +
  <em>15:    var int length = $test->length();</em>
 +
  16:   
 +
  17:    """</body>""";
 +
  18:    """</html>""";
 +
  19: }
 +
 +
You'll notice that the compiler gives us the line and column (how many characters from the start of the line) the error starts on.  The message in this instance is pretty obvious--it's telling us that that the variable <tt>$test</tt> is unknown.  The traceback afterwards probably isn't too useful to us most people, however.
 +
 +
After the error message and traceback, the compiler helpfully gives us some context consisting of the line it had trouble with along with the some surrounding lines.  This helps us find the troublesome place in the code, or see if we can see what the problem is.
 +
 +
To fix this problem, we just need to declare the variable before we use it:
 +
 +
<syntaxhighlight lang="s2">
 +
    var string test = "test";
 +
    var int length = $test->length();
 +
</syntaxhighlight>
 +
 +
=== Mixing up variable types ===
 +
 +
=== Not putting $ in front of a variable being accessed ===
 +
 +
Here's some code where I forgot to put a <tt>$</tt> in front of a variable I am using:
 +
 +
<syntaxhighlight lang="s2">
 +
    var string test = "test";
 +
    var int length = test->length();
 +
</syntaxhighlight>
 +
 +
This is the compiler error I get:
 +
 +
S2 Compiler Output at Thu Jun 17 10:13:02 2010
 +
Error compiling layer:
 +
 +
Compile error: line 15, column 26: Unexpected token found.  Expecting [TokenPunct] = (
 +
Got: [TokenPunct] = ->
 +
  S2::Node, S2/Node.pm, 144
 +
  S2::NodeArguments, S2/NodeArguments.pm, 25
 +
  S2::NodeTerm, S2/NodeTerm.pm, 471
 +
  S2::NodeIncExpr, S2/NodeIncExpr.pm, 41
 +
  S2::NodeTypeCastOp, S2/NodeTypeCastOp.pm, 29
 +
  S2::NodeInstanceOf, S2/NodeInstanceOf.pm, 29
 +
  S2::NodeUnaryExpr, S2/NodeUnaryExpr.pm, 40
 +
  S2::NodeProduct, S2/NodeProduct.pm, 28
 +
  S2::NodeSum, S2/NodeSum.pm, 31
 +
  S2::NodeRelExpr, S2/NodeRelExpr.pm, 29
 +
  S2::NodeEqExpr, S2/NodeEqExpr.pm, 29
 +
  S2::NodeLogAndExpr, S2/NodeLogAndExpr.pm, 29
 +
  S2::NodeLogOrExpr, S2/NodeLogOrExpr.pm, 29
 +
  S2::NodeRange, S2/NodeRange.pm, 29
 +
  S2::NodeCondExpr, S2/NodeCondExpr.pm, 29
 +
  S2::NodeAssignExpr, S2/NodeAssignExpr.pm, 29
 +
  S2::NodeExpr, S2/NodeExpr.pm, 29
 +
  S2::NodeVarDeclStmt, S2/NodeVarDeclStmt.pm, 33
 +
  S2::NodeStmt, S2/NodeStmt.pm, 62
 +
  S2::NodeStmtBlock, S2/NodeStmtBlock.pm, 43
 +
  S2::NodeFunction, S2/NodeFunction.pm, 104
 +
  S2::Layer, S2/Layer.pm, 59
 +
  S2::Compiler, S2/Compiler.pm, 27
 +
 
 +
 +
Context
 +
 +
  11:    """</head>""";
 +
  12:    """<body>""";
 +
  13:
 +
  14:    var string test = "test";
 +
  <em>15:    var int length = test->length();</em>
 +
  16:   
 +
  17:    """</body>""";
 +
  18:    """</html>""";
 +
  19: }
 +
 +
You'll note that the compiler error doesn't tell us exactly what the problem is.  It tells us what "token" (part of the programming language) it was expecting, and what it got.
 +
 +
I'm going to put a bracket set ([]) into the exact position the compile error is complaining about:
 +
 +
var int length = test[]->length();</em>
 +
 +
We can note that if the token the compiler was expecting (<tt>(</tt>) was in that position, it would be as if we were calling a global function. That's because there's no <tt>$</tt> to make the compiler expect a variable instead. If we run through the checklist listed above on this line, however, we'll find that we've broken the rule about <tt>$</tt>s indicating we're using a variable.
 +
 +
To fix the error, we put the <tt>$</tt> character in front of the variable we're trying to access.
 +
 +
<syntaxhighlight lang="s2">
 +
    var string test = "test";
 +
    var int length = $test->length();
 +
</syntaxhighlight>
 +
 +
=== Forgetting the semicolon (;) at the end of a statement ===
 +
 +
=== Forgetting the end parentheses on a function ===
 +
 +
=== Forgetting code block brackets ===
 +
 +
  
 
[[Category: S2 Guide]]
 
[[Category: S2 Guide]]

Revision as of 10:44, 17 June 2010

Syntax checklist

  • Are you ending all statements with a semicolon (;)?
  • Have you declared all variables you are using?
  • Are you using $ when you're accessing variables?
  • Do your function calls have matching parentheses?
  • Do your code blocks have matching brackets?

Deciphering compile errors

The layer editor won't let you save a layer that contains compiler errors. Let's say that in the S2 Cookbook: A Testbed Layout, I test some code that has syntax errors where it says "# Code you want to test goes here". Here are some example situations of the kinds of compile errors I can encounter, and their solution.

Forgetting to declare a variable

Let's make a really easy error first, to get through the basics. Here's an example where I forget to declare the $test variable before I use it: 

    var int length = $test->length();

When I try to save and compile, this is the compiler error I get: 

 S2 Compiler Output at Thu Jun 17 10:23:17 2010
Error compiling layer:

Compile error: line 15, column 22: Unknown local variable $test
  S2::NodeVarRef, S2/NodeVarRef.pm, 180
  S2::NodeVarRef, S2/NodeVarRef.pm, 151
  S2::NodeTerm, S2/NodeTerm.pm, 182
  S2::NodeTerm, S2/NodeTerm.pm, 66
  S2::NodeExpr, S2/NodeExpr.pm, 46
  S2::NodeVarDeclStmt, S2/NodeVarDeclStmt.pm, 54
  S2::NodeStmtBlock, S2/NodeStmtBlock.pm, 108
  S2::NodeFunction, S2/NodeFunction.pm, 230
  S2::Checker, S2/Checker.pm, 374
  S2::Compiler, S2/Compiler.pm, 34
  

Context

 11:     """</head>""";
 12:     """<body>""";
 13: 
 14: 
 15:     var int length = $test->length();
 16:     
 17:     """</body>""";
 18:     """</html>""";
 19: }

You'll notice that the compiler gives us the line and column (how many characters from the start of the line) the error starts on. The message in this instance is pretty obvious--it's telling us that that the variable $test is unknown. The traceback afterwards probably isn't too useful to us most people, however.

After the error message and traceback, the compiler helpfully gives us some context consisting of the line it had trouble with along with the some surrounding lines. This helps us find the troublesome place in the code, or see if we can see what the problem is.

To fix this problem, we just need to declare the variable before we use it: 

    var string test = "test";
    var int length = $test->length();

Mixing up variable types

Not putting $ in front of a variable being accessed

Here's some code where I forgot to put a $ in front of a variable I am using: 

    var string test = "test";
    var int length = test->length();

This is the compiler error I get: 

S2 Compiler Output at Thu Jun 17 10:13:02 2010
Error compiling layer:

Compile error: line 15, column 26: Unexpected token found.  Expecting [TokenPunct] = (
Got: [TokenPunct] = ->
  S2::Node, S2/Node.pm, 144
  S2::NodeArguments, S2/NodeArguments.pm, 25
  S2::NodeTerm, S2/NodeTerm.pm, 471
  S2::NodeIncExpr, S2/NodeIncExpr.pm, 41
  S2::NodeTypeCastOp, S2/NodeTypeCastOp.pm, 29
  S2::NodeInstanceOf, S2/NodeInstanceOf.pm, 29
  S2::NodeUnaryExpr, S2/NodeUnaryExpr.pm, 40
  S2::NodeProduct, S2/NodeProduct.pm, 28
  S2::NodeSum, S2/NodeSum.pm, 31
  S2::NodeRelExpr, S2/NodeRelExpr.pm, 29
  S2::NodeEqExpr, S2/NodeEqExpr.pm, 29
  S2::NodeLogAndExpr, S2/NodeLogAndExpr.pm, 29
  S2::NodeLogOrExpr, S2/NodeLogOrExpr.pm, 29
  S2::NodeRange, S2/NodeRange.pm, 29
  S2::NodeCondExpr, S2/NodeCondExpr.pm, 29
  S2::NodeAssignExpr, S2/NodeAssignExpr.pm, 29
  S2::NodeExpr, S2/NodeExpr.pm, 29
  S2::NodeVarDeclStmt, S2/NodeVarDeclStmt.pm, 33
  S2::NodeStmt, S2/NodeStmt.pm, 62
  S2::NodeStmtBlock, S2/NodeStmtBlock.pm, 43
  S2::NodeFunction, S2/NodeFunction.pm, 104
  S2::Layer, S2/Layer.pm, 59
  S2::Compiler, S2/Compiler.pm, 27
 

Context

 11:     """</head>""";
 12:     """<body>""";
 13: 
 14:     var string test = "test";
 15:     var int length = test->length();
 16:     
 17:     """</body>""";
 18:     """</html>""";
 19: }

You'll note that the compiler error doesn't tell us exactly what the problem is. It tells us what "token" (part of the programming language) it was expecting, and what it got.

I'm going to put a bracket set ([]) into the exact position the compile error is complaining about: 

var int length = test[]->length();</em>

We can note that if the token the compiler was expecting (() was in that position, it would be as if we were calling a global function. That's because there's no $ to make the compiler expect a variable instead. If we run through the checklist listed above on this line, however, we'll find that we've broken the rule about $s indicating we're using a variable.

To fix the error, we put the $ character in front of the variable we're trying to access. 

    var string test = "test";
    var int length = $test->length();

Forgetting the semicolon (;) at the end of a statement

Forgetting the end parentheses on a function

Forgetting code block brackets

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