Question: let keyword about magpie

[haifenghuang]

This is how I design the language: when you define a variable without a value, The magpie language will check if it is ended with a comma, it not, will report an error just like you got.

Is it possible to fix this?
Yes, if you really want to fix it, You can check parseLetStatement function in parser.go file:

1 func (p *Parser) parseLetStatement(inClass bool) *ast.LetStatement {
2	stmt := &ast.LetStatement{Token: p.curToken, InClass: inClass}
3	stmt.Doc = p.lineComment
4
5	if p.peekTokenIs(token.LPAREN) {
6		return p.parseLetStatement2(stmt)
7	}
8
9	//parse left hand side of the assignment
10	for {
11		p.nextToken()
12		if !p.curTokenIs(token.IDENT) && !p.curTokenIs(token.UNDERSCORE) {
13			msg := fmt.Sprintf("Syntax Error:%v- expected token to be identifier|underscore, got %s instead.", p.curToken.Pos, p.curToken.Type)
14			p.errors = append(p.errors, msg)
15			return stmt
16		}
17		name := &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
18		stmt.Names = append(stmt.Names, name)
19
20		if !p.peekTokenIs(token.ASSIGN) && !p.curTokenIs(token.SEMICOLON) && !p.peekTokenIs(token.COMMA) {
21			stmt.SrcEndToken = p.curToken
22			return stmt
23		}
24
24		p.nextToken()
25		if p.curTokenIs(token.ASSIGN) || p.curTokenIs(token.SEMICOLON) {
26			break
27		}
28		if !p.curTokenIs(token.COMMA) {
29			msg := fmt.Sprintf("Syntax Error:%v- expected token to be comma, got %s instead.", p.curToken.Pos, p.curToken.Type)
30			p.errors = append(p.errors, msg)
31			return stmt
32		}
33	}

       //.....
       //.....

	return stmt
}

You can add line 20~23 to the parseLetStatement function, that will solve the problem.

Now you can do below:

let a b=10
printf("a=%v\n", a)  //will print 'a=nil'
printf("b=%d\n", b) //will print `b=10`

Through above code woks, but it's ugly. For readability, you can code it like below:

let a
b=10
printf("a=%v\n", a)  //will print 'a=nil'
printf("b=%d\n", b) //will print `b=10`

But... I also think a semicolon after variable a should be better. so I will not modify the source.

@haifenghuang Thanks, now I understood how it works.

[haifenghuang]

I've changed the parsing for let statement, so it now can accept an optional ';' for example:

let x,y
let m,n;

Both are valid let statement now.