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Editorial Team
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Asked: 2026-05-28T03:29:50+00:00

I’m interested in using/overloading the range step operator (.. ..), but I can’t for

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I’m interested in using/overloading the “range step” operator (.. ..), but I can’t for the life of me find out how to use it.

In the documentation it says

// Usage:
start .. step .. finish

but trying that in the F# shell gives errors:

> let x = 1 .. 2 .. 7;;

  let x = 1 .. 2 .. 7;;
  ----------^^

stdin(54,11): error FS0010: Unexpected symbol '..' in binding. Expected incomplete structured construct at or before this point or other token.

However, calling it “explicitly” is possible:

> let x = (.. ..) 1 2 7;;

val x : seq<int>

Is it only possible to use this operator for list/seq construction such as [1..2..7] and seq {1..2..7}?

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1 Answer

  1. Editorial Team

    The spec § 6.3.12 isn’t explicit about it, but the only examples given are within sequence expressions. That, along with the fact that nothing else works, seems to confirm your conclusion.

    FYI – Here are the relevant docs for the range operators.

    Operators.( .. )<^T>
    Operators.( .. .. )<^T,^Step>

    Section 3.8.2 also mentions special handling of (.. ..), so it’s safe to assume it’s subject to limitations/behavior apart from those of typical functions/operators.

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