error-reporting.md

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Error Reporting

Stylus has fantastic error reporting built-in for syntax, parse, and evaluation errors—complete with stack traces, line numbers, and filenames.

Parse Error

Parse error example:

 body
   form input
     == padding 5px

Yielding:

 Error: /Users/tj/Projects/stylus/testing/test.styl:4
   3: '  form input'
   4: '    == padding 5px'

 illegal unary ==

Evaluation Error

This "runtime" or evaluation error is caused by passing a string to border-radius(), instead of the expected Unit (by using our helper ensure(n, 'unit')).

  ensure(val, type)
    unless val is a type
      error('expected a ' + type + ', but got ' + typeof(val))

  border-radius(n)
    ensure(n, 'unit')
    -webkit-border-radius n
    -moz-border-radius n
    border-radius n

  body
    border-radius '5px'

Yielding:

  Error: /Users/tj/Projects/stylus/examples/error.styl:12
    11: ''
    12: 'body'
    13: '  border-radius \'5px\''
    14: ''

  expected a unit, but got string
      at ensure() (/Users/tj/Projects/stylus/examples/error.styl:2)
      at border-radius() (/Users/tj/Projects/stylus/examples/error.styl:5)
      at "body" (/Users/tj/Projects/stylus/examples/error.styl:10)