fsharp / fsharp/fslang-suggestions

Recognize accessing members on delegate constructors as high-precedence applications

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#964 1 comment 2 reactions 0 assignees View on GitHub
approved-in-principle area: syntax
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Description

```fs
type private GetNameDelegate = delegate of Utf8JsonReader -> string
let tokenType = (GetNameDelegate(fun r -> nameof r.TokenType)).Invoke(Utf8JsonReader()) // OK
let tokenType2 = GetNameDelegate(fun r -> nameof r.TokenType).Invoke(Utf8JsonReader()) // FS0001 This expression was expected to have type 'GetNameDelegate' but here has type 'string'
```

https://github.com/fsharp/fslang-suggestions/issues/644 contains a section about High Precedence Application. It is weird for delegate constructors to be excluded from it.

## Pros and Cons

The advantages of making this adjustment to F# are
1. Consistency
2. Convenience
3. Conciseness

The disadvantages of making this adjustment to F# are (none)

## Extra information

Estimated cost (XS, S, M, L, XL, XXL): XS

Related suggestions: #760 - Delegate constructors cannot be used as normal functions - i.e. cannot be piped into (Also opened by me lol)

## Affidavit (please submit!)

Please tick this by placing a cross in the box:
* [x] This is not a question (e.g. like one you might ask on [stackoverflow](http://stackoverflow.com)) and I have searched stackoverflow for discussions of this issue
* [x] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate
* [x] 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:
* [x] This is not a breaking change to the F# language design
* [x] I or my company would be willing to help implement and/or test this

## For Readers

If you would like to see this issue implemented, please click the :+1: emoji on this issue. These counts are used to generally order the suggestions by engagement.

Contributor guide

No contributing guide indexed for this repository

Research direction

Start by reproducing the two delegate-constructor examples in the issue and compare the requested behavior with the High Precedence Application discussion in #644. Review related suggestion #760 for context; done means the unparenthesized member access is recognized as a high-precedence application and the example compiles consistently.

Written by the indexing model from the issue text.

Assessment

Tech stack
fsharp
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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