Types of errors

Various error messages can appear while using AriNET. We can subdivide them in three categories:

• Errors sent to AriNET by the underlying Scheme: These are the most common errors. They often reflect a syntax error. As an example, evaluating:

  (+ 1 't)
  

  will display:

  ERROR -- +: expects type <number> 
  as 2nd argument, given: t; other arguments were: 1
  

  which is a Scheme error.

• Errors sent by AriNET itself. Here is a non-exhaustive list of them:

  Error	Meaning
  Value not in [-1..1]	The value attempted to be assigned to sin,cos (resp. arcsin and arccos) is not in the range -1 to 1
  Contradiction $<number>$ = $<number>$	This appears when trying to give a value to a variable which already has a value. It also occurs if an equation contains an arithmetical mistake.
  Impossible to set a negative value to a square	The value attempted to be assigned to sqr or sqrt is not $> 0$.
  Impossible to set a value $< 0$ to a exponential	The value attempted to be assigned to sqr or sqrt is negative.
  No such variable in the environment : $<variable>$	The variable you are trying to use has not been previously defined, or the command you are attempting to use was misspelled (for example defvariables instead of defvariable)
  unmatched parenthesis, please check them and try once again.	There are too many/too few parenthesis.
  Unable to forget the value	Often appears when the informants are not matching, or when the variable has no value.

  It is important to notice that these errors reflect, most of the time, an arithmetical incoherence in the designed equation.

• The third category of errors should be empty, however as long as computers are programmed by humans, bugs will remain! This version of AriNET has an internal function which catches the errors and tries to determine whether they are user or program related. When detecting a user error the function just displays it, whereas detecting a program error will prompt a message saying it might be a bug.²⁰

Figure 9: The bug reporting window.