Ring/Lessons/Eval() and Debugging

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Eval() and Debugging[edit]

In this chapter we are going to learn about

  • Error Handling using Try/Catch/Done
  • Eval() function
  • Raise() function
  • Assert() function



Try/Catch/Done[edit]

Syntax:

	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[edit]

We 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[edit]

We 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[edit]

We 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