Error Messages on Parser Failures

[kwannoel]

In GitLab by @AlexKnauth on Jun 9, 2021, 23:30

Currently when a program fails to parse, there's no error message, instead it produces a "shorter" output than it should. For example the program

#lang glow
A;
B;
C;

Would parse as (@module A B C) if there are no errors, but parse as (@module A) if there's an parse error in B.

This needs to be changed to add error messages showing exactly what's wrong with B.

[kwannoel]

In GitLab by @AlexKnauth on Jun 29, 2021, 03:05

marked this issue as related to #207

[kwannoel]

In GitLab by @kwanzknoel on Jul 27, 2021, 18:09

assigned to @kwanzknoel

[kwannoel]

In GitLab by @kwanzknoel on Jul 27, 2021, 19:02

To be more specific, there are two issues.

• [ ] Toplevel parser must end with EOF after valid statements and optional expression. !163
• [ ] Better error message / object instead of just returning #f in failing states.

First is incorrect parser logic. This is demonstrated by the above example. Concrete test:

    (test-case "parseStr invalid subsequent statement"
      (assert-equal!
        (parseStr "let a = 1;
                   let b 2;")
        '(@module (def a 1)))))) ;; FIXME: should be #f

It gives false positive for certain incorrect expressions rather than failing.

Second issue is with error reporting. This is demonstrated by:

(import :drewc/smug
        :mukn/glow/compiler/parse/lexical
        :mukn/glow/compiler/parse/expressions
        )

(def parse-result (run Param (lexify "ajskd")))
(def parse-result-2 (run Param (lexify "(aaaaa")))

(displayln parse-result)
(displayln parse-result-2)

Which gives us:

$ gxi toy.ss
#<param #10 id: #<identifier #11 name: "ajskd"> typ: #f> // valid parse result
#f // invalid parse result needs to be more descriptive

Where we get #f rather than a more descriptive error message / object.

You can also look at tests in glow/compiler/parse/t/expressions-test.ss, with expected value #f.

[kwannoel]

In GitLab by @kwanzknoel on Jul 28, 2021, 18:56

mentioned in merge request !163