Introduced 'error' Object and new semantic of 'try' Object

• @Graur
• 18 Jul 2022
• comments

Since 0.25.0 version it is possible to use error object just like this:

[x] > check
  if. > @
    x.eq 0
    error "Can't divide by zero"
    42.div x

Here, the object error causes program termination at the first attempt to dataize it. It encapsulates any other object, which can play the role of an exception that is floating to the upper level.

The object try enables the catching of an error objects and extracting exceptions from them. For example, the following code prints “The 1th argument of ‘int.div’ is invalid: division by zero is infinity” and then “finally”:

QQ.try
  []
    42.div 0 > @
  [e]
    QQ.io.stdout > @
      e
  []
    QQ.io.stdout > @
      "finally"

The object error encapsulates the error message from int.div object and terminates the program.

We can also throw the error through multiple nested try objects:

eq. > @
  QQ.try
    []
      QQ.try > @
        []
          slice. > @
            "some string"
            7
            5
        [e]
          e > @
        []
          "first finally block" > @
    [e]
      e > @
    []
      "second finally block" > @
  "Start index + length must not exceed string length but was 12 > 11"

Here, we get TRUE because string.slice object uses error object. Which encapsulates the error message “Start index + length must not exceed string length but was 12 > 11”. The first try object throws up this encapsulated string to the second try object.

In addition, you can add new behavior to catch errors, or just use them as is. For example, the following code prints “division by zero is infinity, please check the parameter”

QQ.try
  []
    3.div 0 > @
  [e]
    QQ.io.stdout > @
      e.slice 43 28
  []
    QQ.io.stdout > @
      ", please check the parameter"

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