Bad parser error message

[blp]

The following code:

relation X(a: Option<string>, b: Set<string>, c: string)
relation Y(d: string)

for (X(a, b, c)) {
    Some{var d} = match (a) {
        Some{_} -> set_nth(b, 0),
        None -> Some{c},
    } in
    Y(d)
}

provokes the following error, citing the { in Some{var d}:

ddlog: Failed to parse input file: "playpen3.dl" (line 5, column 9):
unexpected "{"
expecting letter or digit, "_", ".", "[", "(", ";" or "}"

But the actual problem is the trailing , in Some{c}, two lines later, and it's very difficult to figure out that's the real problem when it's much farther along than the cited line. I guess the parser must use arbitrary lookahead....

Related to issue #554