add support for negative numbers

fixes #7

example/example.cfg

@@ -5,8 +5,9 @@ primary {
   string = "primary string value";
   integer = 500;
   float = 80.80;
+  negative = -50;
   boolean = true;
-  negative = FALSE;
+  not_true = FALSE;
   nothing = NULL;
   # Include external files
   include "./*.cfg";

forge.go

@@ -26,11 +26,12 @@
 // Config file format:
 //
 //     IDENTIFIER: [_a-zA-Z]+
+//     NUMBERS: [0-9]+
 //
 //     BOOL: 'true' | 'false'
 //     NULL: 'null'
-//     INTEGER: [0-9]+
-//     FLOAT: INTEGER '.' INTEGER
+//     INTEGER: NUMBERS | ('-' NUMBERS)
+//     FLOAT: (NUMBERS '.' NUMBERS) | ('-' NUMBERS . NUMBERS)
 //     STRING: '"' .* '"'
 //     REFERENCE: [IDENTIFIER] ('.' IDENTIFIER)+
 //     VALUE: BOOL | NULL | INTEGER | FLOAT | STRING | REFERENCE

scanner.go

@@ -100,9 +100,13 @@ func (scanner *Scanner) parseIdentifier() {
 	}
 }
 
-func (scanner *Scanner) parseNumber() {
+func (scanner *Scanner) parseNumber(negative bool) {
 	scanner.curTok.ID = token.INTEGER
 	scanner.curTok.Literal = string(scanner.curCh)
+	if negative {
+		scanner.curTok.Literal = "-" + scanner.curTok.Literal
+	}
+
 	digit := false
 	for {
 		scanner.readRune()
@@ -168,7 +172,7 @@ func (scanner *Scanner) NextToken() token.Token {
 	case isLetter(ch) || ch == '_':
 		scanner.parseIdentifier()
 	case isDigit(ch):
-		scanner.parseNumber()
+		scanner.parseNumber(false)
 	case ch == '#':
 		scanner.parseComment()
 	case ch == eof:
@@ -190,6 +194,10 @@ func (scanner *Scanner) NextToken() token.Token {
 			scanner.curTok.ID = token.SEMICOLON
 		case '.':
 			scanner.curTok.ID = token.PERIOD
+		case '-':
+			if isDigit(scanner.curCh) {
+				scanner.parseNumber(true)
+			}
 		}
 	}