Prop.filter (==>) executes property even if condition does not hold about fscheck HOT 4 CLOSED

Due to F#’s eagerness, the right hand side is always executed. There is no practical way I know of FsCheck can avoid this without user intervention. You can wrap the right hand side in Lazy to avoid this.

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See the docs here for more https://fscheck.github.io/FsCheck/Properties.html#Lazy-Properties

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Thanks @kurtschelfthout! That was exactly what I needed to know. :-)

The following code show what I really was trying to achieve: getting FsCheck and Unquote to be friends.

open FsCheck
open FsCheck.FSharp
open Swensen.Unquote

let lazy_test : Quotations.Expr<bool> -> Lazy<unit> = fun expr -> lazy test expr

type ListProperties =
  static member ``explicit lazy`` (xs : int list) : Property =
    (List.length xs > 0) ==>
        lazy test <@ List.head xs::List.tail xs = xs @>
        
  static member ``implizit lazy`` (xs : int list) : Property =
    (List.length xs > 0) ==>
        lazy_test <@ List.head xs::List.tail xs = xs @>

Check.QuickAll<ListProperties> ()

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This issue relates to issue #130 and above code might be relevant for that issue also.

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