Ring/Lessons/Eval() and Debugging
Eval() and Debugging
editIn this chapter we are going to learn about
- Error Handling using Try/Catch/Done
- Eval() function
- Raise() function
- Assert() function
Try/Catch/Done
editSyntax:
Try
Statements...
Catch
Statements...
Done
The statements in the Try block will be executed, if any error happens then the statements in the catch block will be executed.
Inside the catch block we can use the variable cCatchError to get the error message
Example:
Try
see 5/0
Catch
see "Catch!" + nl + cCatchError
Done
Output:
Catch!
Error (R1) : Cann't divide by zero !
Eval() Function
editWe can execute code during the runtime from string using the Eval() function
Syntax:
Eval(cCode)
Example:
Eval("nOutput = 5+2*5 " )
See "5+2*5 = " + nOutput + nl
Eval("for x = 1 to 10 see x + nl next")
Eval("func test see 'message from test!' ")
test()
Output:
5+2*5 = 15
1
2
3
4
5
6
7
8
9
10
message from test!
Raise() Function
editWe can raise an exception using the Raise() function
Syntax:
Raise(cErrorMessage)
The function will display the error message then end the execution of the program.
We can use Try/Catch/Done to avoid exceptions generated by raise() function.
Example:
nMode = 10
if nMode < 0 or nMode > 5 raise("Error : nMode not in the range 1:4") ok
Output:
Line 4 Error : nMode not in the range 1:4
In raise in file tests\raise.ring
Example:
try
testmode(6)
catch
see "avoid raise!"
done
testmode(-1)
func testmode nMode
if nMode < 0 or nMode > 5
raise("Error : nMode not in the range 1:4")
ok
Output:
avoid raise!
Line 12 Error : nMode not in the range 1:4
In raise In function testmode() in file tests\raise2.ring
called from line 7 in file tests\raise2.ring
Assert() Function
editWe can use the Assert() function to test conditions before executing the code
If the test fail the program will be terminated with an error message contains the assert condition.
Syntax:
Assert( condition )
Example:
x = 10
assert( x = 10)
assert( x = 100 )
Output:
Line 3 Assertion Failed!
In assert in file tests\assert.ring