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Error Handling

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Dave Liepmann edited this page Jul 23, 2017 · 31 revisions

Philosophy

Maria provides a safe playground for experimentation. Therefore, errors of all sorts must be caught and translated into humane, beginner-friendly language. These errors should be worded gently and should suggest ways to solve the error.

Those interested in how Maria wraps errors should read src/maria/messages.cljs and related namespaces. 🤓 👍🏾

😇 Specific errors we could handle better 😇

When it comes to the fight against opaque error messages, we are stronger together. 💪🏾 Please feel free to add to this list!

Accidentally using single quotes rather than double quotes

expressions with single-quoted terms, like (circle 'hello') slip through undeclared-var detection and result in "invalid is too many arguments!"

Multiple overloads of a function with the same arity

See https://github.com/yogthos/clojure-error-message-catalog/blob/master/cljs/duplicate-case-test-constant.md for an overview of the error.

We currently catch and reword the initial error, but that is only one-third of the total error message. We still are getting an unwanted follow-up looking like:

Duplicate case test constant '1' on line 1  at line 1 

Error: Duplicate case test constant '1' on line 1  at line 1 
    at new cljs$core$ExceptionInfo (http://localhost:3449/js/compiled/out-user-dev/cljs/core.js:35636:10)
    at Function.cljs.core.ex_info.cljs$core$IFn$_invoke$arity$3 (http://localhost:3449/js/compiled/out-user-dev/cljs/core.js:35712:9)
    at cljs$core$ex_info (http://localhost:3449/js/compiled/out-user-dev/cljs/core.js:35698:26)
    at Function.cljs.analyzer.error.cljs$core$IFn$_invoke$arity$3 (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:1073:26)
    at cljs$analyzer$error (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:1059:28)
    at cljs$analyzer$macroexpand_1 (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:5291:27)
    at Function.cljs.analyzer.analyze_seq.cljs$core$IFn$_invoke$arity$4 (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:5365:41)
    at cljs$analyzer$analyze_seq (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:5337:34)
    at cljs$analyzer$analyze_form (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:5508:34)
    at cljs$analyzer$analyze_STAR_ (http://localhost:3449/js/compiled/out-user-dev/cljs/analyzer.js:5549:38)
{:type :overload-arity, :extra {:name twice}}

Undetected misuse of function as integer

(inc dec) causes ""function cljs$core$dec(x){\nreturn (x - (1));\n}1""

Wrong order of args in HOF causes no response

See https://github.com/yogthos/clojure-error-message-catalog/blob/master/clj/dont-know-how-to-create-iseq-from.md

(map [1 2 3] inc) causes console error 😿, no result 😿, and a broken environment. 💩!

We don't detect misuse of map literals

(:a "B") causes "nil" output, even though we'd like to detect attempted use of key lookups on non-maps and suggest alternatives. See https://github.com/yogthos/clojure-error-message-catalog/blob/master/clj/wrong-num-args-passed-to-keyword.md

Similarly, (:first-name "Bob", :last-name "Bobberton") causes "(intermediate value).cljs$core$IFn$_invoke$arity$3 is not a function\n\nThe function first-name in the expression above needs a different number of arguments.""

Even number of forms in let

We misreport the cause of this. See https://github.com/yogthos/clojure-error-message-catalog/blob/master/clj/let-requires-even-number-forms.md

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