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Explicitly define operand in syntax #395

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Jun 19, 2023
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Explicitly define operand in syntax #395

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Explicitly define operand in syntax
eemeli Jun 17, 2023
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Update spec/syntax.md
eemeli Jun 19, 2023
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3 changes: 2 additions & 1 deletion spec/message.abnf
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,8 @@ selectors = match 1*([s] expression)
variant = when 1*(s key) [s] pattern
key = literal / "*"

expression = "{" [s] (((literal / variable) [s annotation]) / annotation) [s] "}"
expression = "{" [s] ((operand [s annotation]) / annotation) [s] "}"
operand = literal / variable
annotation = (function *(s option)) / reserved

literal = quoted / unquoted
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30 changes: 16 additions & 14 deletions spec/syntax.md
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Expand Up @@ -125,30 +125,24 @@ A simple _expression_ is a bare variable name:
### Formatting Functions

A _function_ is named functionality, possibly with _options_, that format,
process, or operate on a _variable_.
process, or operate on an _operand_ which may be either a _literal_ or a _variable_.

For example, a _message_ with an interpolated `$date` _variable_ formatted with the `:datetime` _function_:
For example, a _message_ with a `$date` _variable_ formatted with the `:datetime` _function_:

{Today is {$date :datetime weekday=long}.}

A _message_ with an interpolated `$userName` _variable_ formatted with
A _message_ with a `$userName` _variable_ formatted with
the custom `:person` _function_ capable of
declension (using either a fixed dictionary, algorithmic declension, ML, etc.):

{Hello, {$userName :person case=vocative}!}

A _message_ with an interpolated `$userObj` _variable_ formatted with
A _message_ with a `$userObj` _variable_ formatted with
the custom `:person` _function_ capable of
plucking the first name from the object representing a person:

{Hello, {$userObj :person firstName=long}!}

Functions use one of the following prefix sigils:

- `:` for standalone content
- `+` for starting or opening elements
- `-` for ending or closing elements

A message with two markup-like _functions_, `button` and `link`,
which the runtime can use to construct a document tree structure for a UI framework:

Expand Down Expand Up @@ -347,19 +341,27 @@ Whitespace within a _pattern_ is meaningful and MUST be preserved.

### Expressions

**_Expressions_** MUST start with a _literal_, a _variable_, or an _annotation_.
**_Expressions_** MUST start with an _operand_ or an _annotation_.
An _expression_ MUST NOT be empty.

A _literal_ or _variable_ MAY be optionally followed by an _annotation_.
An **_operand_** is either a _literal_ or a _variable_.
An _operand_ MAY be optionally followed by an _annotation_.

An **_annotation_** consists of a _function_ and its named _options_,
or consists of a _reserved_ sequence.

_Functions_ do not accept any positional arguments
other than the _literal_ or _variable_ in front of them.
other than the _operand_ in front of them.

_Functions_ use one of the following prefix sigils:

- `:` for standalone content
- `+` for starting or opening _expressions_
- `-` for ending or closing _expressions_

```abnf
expression = "{" [s] (((literal / variable) [s annotation]) / annotation) [s] "}"
expression = "{" [s] ((operand [s annotation]) / annotation) [s] "}"
operand = literal / variable
annotation = (function *(s option)) / reserved
option = name [s] "=" [s] (literal / variable)
```
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