Add std.parseFloat

[elkotito]

I would like to suggest a feature to parse strings into float numbers. I haven't found std.parseFloat() function in https://jsonnet.org/ref/stdlib.html. Since std.extVar returns a string it's impossible to use float numbers as external variables.

In my case, it would be useful since I used jsonnet to describe experiments in AllenNLP framework as sometimes I pass hyperparameters like learning rate as an environmental variable. Although I could obviously pass them using a top-level function, some platforms like Polyaxon requires to pass them as environmental variables.

[sbarzowski]

Since std.extVar returns a string it's impossible to use float numbers as external variables.

Not necessarily. You can do something like:

21x.jsonnet:

std.extVar('foo') * 21

Command to run (see that --ext-code is used rather than --ext-var):

jsonnet --ext-code foo=2 21x.jsonnet

[sbarzowski]

That said, parseFloat would be a useful addition to stdlib.

[sbarzowski]

Workaround: use std.parseJson, which can also parse a float as a special case:

$ ./jsonnet -e 'std.parseJson("3.14")'
3.1400000000000001

[elkotito]

Thank you for the workaround!

[seh]

Workaround: use std.parseJson, which can also parse a float as a special case:

That's what we've done. It's not easy to discover that workaround the first time, but it does work well enough so far.

[glenntrewitt]

I need to be able to parse a float that isn't an external variable. Unfortunately, std.parseJson has a little problem:

% jsonnet -e 'std.parseJson("x3.1")'
Something went wrong during jsonnet_evaluate_snippet, please report this: [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'

[sbarzowski]

The error is not ideal and should be fixed (it shouldn't just crash) and it should be fixed. That said, "x3.1" is not a valid float, so I don't see how std.parseFloat would help you here.

[eladsegal]

std.parseJson("1.0") is parsed as 1 (int) instead of 1.0 (float).
Is there a workaround for this?

[glenntrewitt]

I was just fooling around to see what would happen. I'd have expected a failure, of course.
What I actually want to do is to validate a string that contains a bunch of numbers. I think that failing on such an assertion is OK for many purposes, but if you want to check that a string encodes a number as a option, you're out of luck.

What I'd really like to see is support for regexp matching.

[sbarzowski]

@eladsegal

std.parseJson("1.0") is parsed as 1 (int) instead of 1.0 (float).

There's no separate int type in Jsonnet. A floating point number 1.0 is printed out as 1. (That's the same behavior as in JS).