Ring/Lessons/Eval() and Debugging

Eval() and Debugging In this chapter we are going to learn about Error Handling using Try/Catch/Done Eval() function Raise() function Assert() function Try/Catch/Done 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 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 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 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 Ring programming language