Allow units of measure in sequence ranges #535

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marklam opened this Issue Feb 9, 2017 · 2 comments

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@marklam
marklam commented Feb 9, 2017

Allow units of measure in sequence ranges

I propose we extend sequence expressions to handle ranges involving units of measure. Currently we cannot do the following:

let maximumDistance = 3<km>
let minimumDistance = 1<km>
let trials = [ minimumDistance .. maximumDistance ]

The existing way of approaching this problem in F# is to generate a range from bare integers and then map a multiplication to add the dimension

Pros and Cons

The advantages of making this adjustment to F# are

  • An improvement to the safety of code by removing error potential in dropping the units and then adding them back
  • More concise, readable code

The disadvantages of making this adjustment to F# are

  • None that I can think of

Extra informtion

Estimated cost (XS, S, M, L, XL, XXL):
M? (because of the added complication of min .. step .. max)

Related suggestions: (put links to reated suggestions here)
Allow units of measure in for loops #534

Affadavit (must be submitted)

Please tick this by placing a cross in the box:

  • This is not a question (e.g. like one you might ask on stackoverflow) and I have searched stackoverflow for discussions of this issue
  • I have searched both open and closed suggestions on this site and believe this is not a duplicate
  • This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it.

Please tick all that apply:

  • This is not a breaking change to the F# language design
  • I would be willing to help test this
  • I or my company would be willing to help crowdfund F# Software Foundation members to work on this
@marklam marklam referenced this issue Feb 9, 2017
Open

Allow units of measure in for loops #534

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@gmpl
gmpl commented Feb 10, 2017

Looks like the problem is that units of measure don't support the GenericOne operator, possibly because being a measure, which is basically a multiplication, 'zero' is an absolute value but 'one' is relative to the measure.

Since the (..) operator uses the GenericOne it doesn't work, of course you can write this:

let trials = [ minimumDistance .. 1<km> .. maximumDistance ]

Alternatively, or if this suggestion doesn't get approved, you can suggest to add GenericOne to a library that offers language extensions, like FSharpPlus which will redefine some generic operators, like (..) so the code you posted would work, but will be interesting to understand the reason why it wasn't added to F# in first place.

@marklam
marklam commented Feb 13, 2017

Cool, I didn't know that adding measure to the steps would work!

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