# Hat 1.12 Bugs and Limitations

This is a list of some known limitations and bugs in Hat 1.12. Please mail nhc-bugs@haskell.org to report any other problems you find.

### Compile-time problems:

Type variables of higher kinds have only limited support.
Libraries Time and Locale are missing.
Rarely, the compiler fails with heap overrun.
Very rarely, the compiler fails with No match in _dCaf.
More details about compile-time problems are listed here.

### Run-time problems:

Programs that exhaust memory fail with no trace.
Strictness annotations in data type definitions lose their effect.

### Problems with viewing a trace

#### General

Records are not traced at source level.
List comprehensions are not traced at source level.
Monadic do expressions are not traced at source level.
Some numeric expressions are not traced at source level.
Super-saturated applications are not shown correctly.
Traces involving pattern bindings may be incomplete.

#### Hat-observe

Hat-observe cannot compare infinite data structures attempting to generalise across several equations. Use Ctrl-C to kill it.

#### Hat-detect

Only useable for computations that produce faulty output, not for computations that abort with an error message or are interrupted.
Does not work correctly for programs that read input.

#### Hat-trail

Scrolling sometimes blanks the upper part of the display when the trace is extended and is deeper than the window.
If the output is empty, it cannot be selected.

More details about browser bugs and wishes are listed here.

This page last modified: 15 Mar 2002