How to test the "Hello" lexer and parser with invalid source code? I have created the "Hello" grammar and generated the "Hello" lexer and parser.

To test the "Hello" lexer and parser with invalid source code, we need to review the "Hello" grammar again.

\fyicenter>more hello.g4

// Define a grammar called Hello
grammar Hello;
r  : 'hello' ID ;         // match keyword hello followed by an identifier
ID : [a-z]+ ;             // match lower-case identifiers
WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines

The "Hello" grammar file contains:

• One rule called "r". It starts with the keyword "hello" and is followed by an "ID" token.
• The "ID" token must be one or more lower case characters.
• All white space characters are ignored.

So the following source code lines should be valid:

hello you
hello there
hello hello

And the following source code lines are invalid:

Hello you
hello you!
hello Joe
hello 123

If you run the TestRig with invalid source code lines, you will get syntax errors from the parser:

\fyicenter>java -cp .;antlr-4.10.1-complete.jar org.antlr.v4.gui.TestRig Hello r -tree

Hello you
^Z
line 1:0 token recognition error at: 'H'
line 1:1 missing 'hello' at 'ello'
(r <missing 'hello'> ello)


\fyicenter>java -cp .;antlr-4.10.1-complete.jar org.antlr.v4.gui.TestRig Hello r -tree
   
hello you!
^Z
line 1:9 token recognition error at: '!'
(r hello you)


\fyicenter>java -cp .;antlr-4.10.1-complete.jar org.antlr.v4.gui.TestRig Hello r -tree

hello Joe
^Z
line 1:6 token recognition error at: 'J'
(r hello oe)


\fyicenter>java -cp .;antlr-4.10.1-complete.jar org.antlr.v4.gui.TestRig Hello r -tree

hello 123
^Z
line 1:6 token recognition error at: '1'
line 1:7 token recognition error at: '2'
line 1:8 token recognition error at: '3'
line 2:0 missing ID at '<EOF>'
(r hello <missing ID>)

⇒ ANTLR TestRig Graphical Output

⇐ ANTLR "Hello" Grammar File and Test

⇑ ANTLR Commands and Examples

⇑⇑ FAQ for ANTLR Parser Generator