Any insights of why scope has limited syntax supported?

[y-nk]

Hello,

I'm trying to build some math expressions mapped to a db, and i would have liked to go for {deadbeefdeadbeefdeadbeef}.value + {0123456789abcdef01234567}.value

provided that i pass a scope such as:

const scope = {
  ['{deadbeefdeadbeefdeadbeef}.value']: 1,
  ['{0123456789abcdef01234567}.value']: 2,
}

but i hit an error Colon: expected after object key

Any idea of how to have a good looking thing? i could eventually go for ['', dbId, 'value'].join('_') but i was more intrigued by the limitation.

Thanks :)

[gwhitney]

I don't think I am quite understanding the question. The string {foo}.value is currently a syntax error as a mathjs expression, because the curly brackets {...} are currently only used for ordinary JavaScript object notation {key1: value1, key2: value2}, etc. There is no way that the contents of a scope object used in evaluating an expression can affect whether that expression is syntactically valid or not.

So for example, even with a scope like const myscope = {'-3^2': 17} then math.evaluate('-3^2', myscope) is still of course -9, because the value of the expression -3^2 is always -9 -- it never even consults the scope, because all that occurs in that expression are numerical constants and known operations. In general, the scope is only consulted for identifiers that occur in the expression, and identifiers have a specific syntax (generally speaking, sequences of characters that start with an alphabetic (or _ or $) and consist only of alphanumeric characters (or _ or $).

[y-nk]

@gwhitney i think it's my misunderstanding on how scope replacement works then.

i was under the impression that there would be a string replacement in the formula before evaluation as (for example) Object.entries(scope).forEach(([key, val]) => formula.replaceAll(key, val)) as a preliminary step, but it seems it's rather not the case and closer to a with (scope) {} block (if anyone can remember those).

the expectation was that i could type literally any string as key and it would be replaced by its value in the formula. in your example math.evaluate('-3^2', {'-3^2': 17 }) would then have had the 1st pass of replacing -3^2 by 17 then evaluating the math of it and therefore returning 17.

in the meantime i changed my convention from {objId}.prop to be __objId_prop__ and it works ok since it's valid javascript.

[gwhitney]

Indeed, the scope is not used for string replacement at all, but rather as the (first) place to look for the values of identifiers as the (abstract syntax tree of the parsed) expression is evaluated.

Closing this discussion.