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[RFC] Add more proposed mods to ABNF grammar.

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Alessandro Coglio 2021-08-23 14:39:59 -07:00
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53
docs/rfc/007-type-aliases.md
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@ -42,7 +42,7 @@ With the array types of unspecified size proposed in RFC 006,
## Syntax
The ABNF grammar changes as follows:
```ts
```
; modified rule:
keyword = ...
/ %s"true"
@ -59,12 +59,63 @@ declaration = import-declaration
/ circuit-declaration
/ constant-declaration
/ type-alias-declaration ; new
```
A type alias declaration introduces the identifier to stand for the type.
Only top-level type alias declarations are supported;
they are not supported inside functions or circuit types.
In addition, the following changes to the grammar are appropriate.
First, the rule
```
circuit-type = identifier / self-type ; replace with the one below
```
should be replaced with the rule
```
circuit-or-alias-type = identifier / self-type
```
The reason is that, at parsing time, an identifier is not necessarily a circuit type;
it may be a type alias that may expand to a (circuit or non-circuit type).
Thus, the nomenclature `circuit-or-alias-type` is appropriate.
Consequently, references to `circuit-type` in the following rules must be replaced with `circuit-or-alias-type`:
```
; modified rule:
circuit-construction = circuit-or-alias-type "{" ; modified
circuit-inline-element
*( "," circuit-inline-element ) [ "," ]
"}"
; modified rule:
postfix-expression = primary-expression
/ postfix-expression "." natural
/ postfix-expression "." identifier
/ identifier function-arguments
/ postfix-expression "." identifier function-arguments
/ circuit-or-alias-type "::" identifier function-arguments ; modified
/ postfix-expression "[" expression "]"
/ postfix-expression "[" [expression] ".." [expression] "]"
```
Second, the rule
```
aggregate-type = tuple-type / array-type / circuit-type
```
should be removed, because if we replaced `circuit-type` with `circuit-or-alias-type` there,
the identifier could be a type alias, not necessarily an aggregate type.
(The notion of aggregate type remains at a semantic level, but has no longer a place in the grammar.)
Consequently, the rule
```
type = scalar-type / aggregate-type
```
should be rephrased as
```
type = scalar-type / tuple-type / array-type / circuit-or-alias-type
```
which "inlines" the previous `aggregate-type` with `circuit-type` replaced with `circuit-or-alias-type`.
## Semantics
There must be no direct or indirect circularity in the type aliases.