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:

  ParseError: test.styl:3:16
    1| body
    2|    form input
    3|      == padding 5px
 ---------------------^
    4|

  illegal unary "==", missing left-hand operand

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: test.styl:3:62
    1| ensure(val, type)
    2|     unless val is a type
    3|       error('expected a ' + type + ', but got ' + typeof(val))
 -------------------------------------------------------------------^
    4|
    5| border-radius(n)
    6|   ensure(n, 'unit')

  expected a unit, but got string
      at ensure() (test.styl:2:17)
      at border-radius() (test.styl:6:16)
      at "body" (test.styl:10:18)