doc/ref: allow embeding to be Expression
And implementation.
Change-Id: I63f2b7b91e0635d071311346e216729f87b21b2e
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/3188
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index 3569fa8..4945ffa 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -1165,12 +1165,11 @@
carefully.
-->
```
-StructLit = "{" [ DeclarationList [ "," [ "..." ] ] "}" .
-DeclarationList = Declaration { "," Declaration }
-Declaration = FieldDecl | DefinitionDecl | AliasDecl | ComprehensionDecl | Embedding .
+StructLit = "{" { Declaration "," } [ "..." ] "}" .
+Declaration = FieldDecl | DefinitionDecl | AliasDecl | Comprehension | Embedding .
FieldDecl = Label { Label } ":" Expression { attribute } .
DefinitionDecl = Label "::" Expression { attribute } .
-Embedding = Operand .
+Embedding = Expression .
AliasDecl = Label "=" Expression .
BindLabel = "<" identifier ">" .
@@ -1178,10 +1177,6 @@
ExpressionLabel = BindLabel
Label = ConcreteLabel [ "?" ] | ExpressionLabel .
-<!-- (jba) According to this grammar, I must write a "?" after a bind label, so
-"<Name>: name" is illegal.
--->
-
attribute = "@" identifier "(" attr_elems ")" .
attr_elems = attr_elem { "," attr_elem }
attr_elem = attr_string | attr_label | attr_nest .
@@ -1302,6 +1297,9 @@
A struct resulting from such a unification is closed if either of the involved
structs were closed.
+Syntactically, embeddings may be any expression except that it only
+allows binary expressions with operators `&` or `|`.
+
```
S1: {
a: 1
@@ -1619,11 +1617,6 @@
of all fields with the same identifier.
String labels do not bind an identifier to the respective field.
-```
-TopLevelDecl = Declaration | Emit .
-Emit = Operand .
-```
-
The _scope_ of a declared identifier is the extent of source text in which the
identifier denotes the specified field, alias, or package.
@@ -2596,7 +2589,7 @@
resulting in the unification of their values.
```
-ComprehensionDecl = Clauses StructLit .
+Comprehension = Clauses StructLit .
ListComprehension = "[" Expression Clauses "]" .
Clauses = Clause { Clause } .
@@ -2877,9 +2870,22 @@
packages whose contents it wishes to use, followed by a possibly empty set of
declarations.
+Like with a struct, a source file may contain embeddings.
+Unlike with a struct, the embedded expressions may be any value.
+If the result of the unification of all embedded values is not a struct,
+it will be output instead of its enclosing file when exporting CUE
+to a data format
```
-SourceFile = [ PackageClause "," ] { ImportDecl "," } { TopLevelDecl "," } .
+SourceFile = [ PackageClause "," ] { ImportDecl "," } { Declaration "," } .
+```
+
+```
+"Hello \(place)!"
+
+place: "world"
+
+// Outputs "Hello world!"
```
### Package clause
