Troubleshooting

Texl never stops with an error. When something goes wrong, the output shows it in one of the ways below.

The output contains [[Undefined]]

An operation in the tag was invalid. Find out which one by inspecting the value with undef.inspect. Show the members of the description, or a few of them:

<% e = undef.inspect ("Total" + 10) %><% e.type %>: <% e.op %> of <% e.lhv %> and <% e.rhv %>

BinaryOperation: sum of Total and 10

Here the sum of a text and a number is invalid. The fix is "Total" + text.from 10.

pos tells where the error is, counted in bytes from the start of the tag's content (just after <%). Errors raised by built-in functions report 0.

The most common causes are:

• mixing types: "Total: " + 10, or a number given to a text function;
• a missing argument, which makes it Nothing: add 3 instead of add (3, 4);
• calling the wrong value: f g x instead of f (g x) (see pitfalls);
• a syntax error, such as a missing bracket or a single-quoted text.

A value is missing

If a tag writes nothing where you expected a value:

• Check the spelling. A misspelled name is Nothing, and Nothing writes nothing.
• Check that the name is bound before the tag. Tags run in order, and a name bound in a later tag is not yet available.
• Check the host's globals. Is the data you expect actually passed to the template?
• Check ? conditions. cond ? value writes nothing when the condition is false.

Give optional names a default to make missing values visible: <% customer.name ; "MISSING NAME" %>.

The output contains [[List of N]], [[Namespace of N]] or [[Func]]

The tag's value is a list, a namespace or a function, which have no text form.

• For a list, write its items: list.enum items, or text.join ", " (list.enum items).
• For a namespace, pick a member: customer.name.
• For a function, you probably forgot to call it: today () instead of today.

The output contains [[Pending Promise]]

A promise inside a tuple, or inside another value, was not ready when the tag was written. Only a promise returned by the tag itself is awaited. See Several promises.

Values are separated by commas

The tag's value is a tuple, which is written as its items separated by , . Often this is a sequence of steps whose intermediate values are not Nothing: use = rather than : for the intermediate steps. To join items with another separator, use text.join.

Unexpected empty lines

A tag alone on its line leaves the line break behind. See Line breaks around tags.

Rendering crashes with a stack overflow

A recursive function never reaches the case that stops it. Check that the condition that ends the recursion is reached for every input. See Evaluation order.

Part of the template is copied as it is

A <% without a matching %> makes the rest of the template plain text. A %> inside a text literal ends the tag early. See Writing the delimiters as text.

Known issues

• Infinite recursion stops the program instead of producing Undefined.