Merge pull request #689 from jvalue/rfc-0021

RFC 0021: Sheet row syntax

Author: jrentlez

rfc/0021-sheet-row-access-syntax/README.md

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+<!--
+SPDX-FileCopyrightText: 2023 Friedrich-Alexander-Universitat Erlangen-Nurnberg
+
+SPDX-License-Identifier: AGPL-3.0-only
+-->
+
+# RFC 0021: Sheet row access syntax
+
+| | |
+|---|---|
+| Feature Tag | `sheet-row-access-syntax` |
+| Status | `ACCEPTED` |
+| Responsible | `jrentlez` |
+<!-- 
+  Status Overview:
+  - DRAFT: The RFC is not ready for a review and currently under change. Feel free to already ask for feedback on the structure and contents at this stage.
+  - DISCUSSION: The RFC is open for discussion. Usually, we open a PR to trigger discussions.
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+
+## Summary
+
+This RFC removes an unnecessary definition of RFC 0020 regarding sheet row
+access.
+
+## Motivation
+
+The `[]` syntax introduced in RFC 0020 is a completely new concept to new users.
+
+## Explanation
+
+Below is the current way of accessing the values of a sheet row, as specified
+in RFC 0020:
+
+```jayvee
+transform Parser {
+  from row oftype SheetRow;
+  to coord oftype Coordinate;
+
+  coord: {
+    x: asInteger row["x"],
+    y: asInteger row[2],
+  }
+}
+```
+
+### `.` replaces `[]`
+
+`row[2]` is a familiar syntax for accessing a collection.
+But at a deeper level, `[]` is a function that takes a collection and a
+"location" and returns the collection's value at the "location".
+
+Jayvee already has a concept for this, operators.
+As a consequence, the `[]` syntax is replaced with the new binary operator `.`.
+
+```jayvee
+coord: {
+  // Both notations (with and without spaces around `.`) are valid.
+  x: asInteger (row . "x"),
+  y: asInteger (row.2),
+}
+```
+
+## Drawbacks
+
+- Parentheses may be mistaken as a function call
+
+## Alternatives
+
+### `.`'s name
+
+We could use a "speaking name" for `.` e.g. `cellInColumn`.
+
+Pros:
+  - If the name is well chosen, it's obvious what the operator does
+
+Cons:
+  - `cellInColumn` would be used very frequently, creating lots of visual
+  "noise".
+  - We are committing to the singular function of this operator and cannot
+    expand it in the future
+
+### `.` precedence
+
+`.` has the highest precedence out of all binary and ternary operators, but a
+lower precedence than unary operators (RFC 0009).
+This results in braces being necessary (see example above).
+We could make an exception and give `.` the highest precedence out of all
+operators, which would enable the following:
+
+```jayvee
+someValue: {
+  x: asInteger row . "x",
+  y: asInteger row.2,
+  z: asInteger row."x",
+}
+```
+
+## Possible Future Changes/Enhancements
+
+- We may be able to unify the `.` operator and the nested property access from
+  RFC 0018.