Parse `show` and `wrap` expressions

9 files changed, 148 insertions, 2 deletions

diff --git a/src/diag.rs b/src/diag.rs
index be431e12..bd91df26 100644
--- a/src/diag.rs
+++ b/src/diag.rs
@@ -76,7 +76,10 @@ pub trait At<T> {
     fn at(self, span: Span) -> TypResult<T>;
 }
 
-impl<T> At<T> for StrResult<T> {
+impl<T, S> At<T> for Result<T, S>
+where
+    S: Into<String>,
+{
     fn at(self, span: Span) -> TypResult<T> {
         self.map_err(|message| Error::boxed(span, message))
     }
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 58400f5a..2023004f 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -383,6 +383,8 @@ impl Eval for Expr {
             Self::Binary(v) => v.eval(ctx),
             Self::Let(v) => v.eval(ctx),
             Self::Set(v) => v.eval(ctx),
+            Self::Show(v) => v.eval(ctx),
+            Self::Wrap(v) => v.eval(ctx),
             Self::If(v) => v.eval(ctx),
             Self::While(v) => v.eval(ctx),
             Self::For(v) => v.eval(ctx),
@@ -759,6 +761,22 @@ impl Eval for SetExpr {
     }
 }
 
+impl Eval for ShowExpr {
+    type Output = Value;
+
+    fn eval(&self, _: &mut EvalContext) -> TypResult<Self::Output> {
+        Err("show rules are not yet implemented").at(self.span())
+    }
+}
+
+impl Eval for WrapExpr {
+    type Output = Value;
+
+    fn eval(&self, _: &mut EvalContext) -> TypResult<Self::Output> {
+        Err("wrap is not yet implemented").at(self.span())
+    }
+}
+
 impl Eval for IfExpr {
     type Output = Value;
 
diff --git a/src/parse/incremental.rs b/src/parse/incremental.rs
index 4c82f158..2edb84ba 100644
--- a/src/parse/incremental.rs
+++ b/src/parse/incremental.rs
@@ -466,10 +466,13 @@ impl NodeKind {
             // how far the expression would go.
             Self::Let
             | Self::Set
+            | Self::Show
+            | Self::Wrap
             | Self::If
             | Self::Else
             | Self::For
             | Self::In
+            | Self::As
             | Self::While
             | Self::Break
             | Self::Continue
@@ -542,6 +545,8 @@ impl NodeKind {
             | Self::IfExpr
             | Self::LetExpr
             | Self::SetExpr
+            | Self::ShowExpr
+            | Self::WrapExpr
             | Self::ImportExpr
             | Self::IncludeExpr => SuccessionRule::AtomicPrimary,
 
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index a9752645..72d38b46 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -208,6 +208,8 @@ fn markup_node(p: &mut Parser, at_start: &mut bool) {
         NodeKind::Ident(_)
         | NodeKind::Let
         | NodeKind::Set
+        | NodeKind::Show
+        | NodeKind::Wrap
         | NodeKind::If
         | NodeKind::While
         | NodeKind::For
@@ -275,7 +277,14 @@ fn enum_node(p: &mut Parser, at_start: bool) {
 /// Parse an expression within markup mode.
 fn markup_expr(p: &mut Parser) {
     if let Some(token) = p.peek() {
-        let stmt = matches!(token, NodeKind::Let | NodeKind::Set | NodeKind::Import);
+        let stmt = matches!(
+            token,
+            NodeKind::Let
+                | NodeKind::Set
+                | NodeKind::Show
+                | NodeKind::Wrap
+                | NodeKind::Import
+        );
         let group = if stmt { Group::Stmt } else { Group::Expr };
 
         p.start_group(group);
@@ -388,6 +397,8 @@ fn primary(p: &mut Parser, atomic: bool) -> ParseResult {
         // Keywords.
         Some(NodeKind::Let) => let_expr(p),
         Some(NodeKind::Set) => set_expr(p),
+        Some(NodeKind::Show) => show_expr(p),
+        Some(NodeKind::Wrap) => wrap_expr(p),
         Some(NodeKind::If) => if_expr(p),
         Some(NodeKind::While) => while_expr(p),
         Some(NodeKind::For) => for_expr(p),
@@ -714,6 +725,26 @@ fn set_expr(p: &mut Parser) -> ParseResult {
     })
 }
 
+/// Parse a show expression.
+fn show_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::ShowExpr, |p| {
+        p.eat_assert(&NodeKind::Show);
+        expr(p)?;
+        p.eat_expect(&NodeKind::As)?;
+        expr(p)
+    })
+}
+
+/// Parse a wrap expression.
+fn wrap_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::WrapExpr, |p| {
+        p.eat_assert(&NodeKind::Wrap);
+        ident(p)?;
+        p.eat_expect(&NodeKind::In)?;
+        expr(p)
+    })
+}
+
 /// Parse an if expresion.
 fn if_expr(p: &mut Parser) -> ParseResult {
     p.perform(NodeKind::IfExpr, |p| {
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 840a68e1..eef7a72d 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -540,10 +540,13 @@ fn keyword(ident: &str) -> Option<NodeKind> {
         "with" => NodeKind::With,
         "let" => NodeKind::Let,
         "set" => NodeKind::Set,
+        "show" => NodeKind::Show,
+        "wrap" => NodeKind::Wrap,
         "if" => NodeKind::If,
         "else" => NodeKind::Else,
         "for" => NodeKind::For,
         "in" => NodeKind::In,
+        "as" => NodeKind::As,
         "while" => NodeKind::While,
         "break" => NodeKind::Break,
         "continue" => NodeKind::Continue,
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index bea4ef00..39854052 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -217,6 +217,10 @@ pub enum Expr {
     Let(LetExpr),
     /// A set expression: `set text(...)`.
     Set(SetExpr),
+    /// A show expression: `show heading(body) as [*{body}*]`.
+    Show(ShowExpr),
+    /// A wrap expression: `wrap body in columns(2, body)`.
+    Wrap(WrapExpr),
     /// An if-else expression: `if x { y } else { z }`.
     If(IfExpr),
     /// A while loop expression: `while x { y }`.
@@ -245,6 +249,8 @@ impl TypedNode for Expr {
             NodeKind::WithExpr => node.cast().map(Self::With),
             NodeKind::LetExpr => node.cast().map(Self::Let),
             NodeKind::SetExpr => node.cast().map(Self::Set),
+            NodeKind::ShowExpr => node.cast().map(Self::Show),
+            NodeKind::WrapExpr => node.cast().map(Self::Wrap),
             NodeKind::IfExpr => node.cast().map(Self::If),
             NodeKind::WhileExpr => node.cast().map(Self::While),
             NodeKind::ForExpr => node.cast().map(Self::For),
@@ -270,6 +276,8 @@ impl TypedNode for Expr {
             Self::With(v) => v.as_red(),
             Self::Let(v) => v.as_red(),
             Self::Set(v) => v.as_red(),
+            Self::Show(v) => v.as_red(),
+            Self::Wrap(v) => v.as_red(),
             Self::If(v) => v.as_red(),
             Self::While(v) => v.as_red(),
             Self::For(v) => v.as_red(),
@@ -288,6 +296,8 @@ impl Expr {
                 | Self::Call(_)
                 | Self::Let(_)
                 | Self::Set(_)
+                | Self::Show(_)
+                | Self::Wrap(_)
                 | Self::If(_)
                 | Self::While(_)
                 | Self::For(_)
@@ -914,6 +924,40 @@ impl IncludeExpr {
 }
 
 node! {
+    /// A show expression: `show heading(body) as [*{body}*]`.
+    ShowExpr
+}
+
+impl ShowExpr {
+    /// The pattern that decides which node's appearence to redefine.
+    pub fn pattern(&self) -> Expr {
+        self.0.cast_first_child().expect("show expression is missing pattern")
+    }
+
+    /// The expression that defines the node's appearence.
+    pub fn body(&self) -> Expr {
+        self.0.cast_last_child().expect("show expression is missing body")
+    }
+}
+
+node! {
+    /// A wrap expression: wrap body in columns(2, body)`.
+    WrapExpr
+}
+
+impl WrapExpr {
+    /// The binding to assign the remaining markup to.
+    pub fn binding(&self) -> Ident {
+        self.0.cast_first_child().expect("wrap expression is missing binding")
+    }
+
+    /// The expression to evaluate.
+    pub fn body(&self) -> Expr {
+        self.0.cast_last_child().expect("wrap expression is missing body")
+    }
+}
+
+node! {
     /// An if-else expression: `if x { y } else { z }`.
     IfExpr
 }
diff --git a/src/syntax/highlight.rs b/src/syntax/highlight.rs
index 0f1ee89d..c399b487 100644
--- a/src/syntax/highlight.rs
+++ b/src/syntax/highlight.rs
@@ -136,11 +136,14 @@ impl Category {
             NodeKind::With => Some(Category::Keyword),
             NodeKind::Let => Some(Category::Keyword),
             NodeKind::Set => Some(Category::Keyword),
+            NodeKind::Show => Some(Category::Keyword),
+            NodeKind::Wrap => Some(Category::Keyword),
             NodeKind::If => Some(Category::Keyword),
             NodeKind::Else => Some(Category::Keyword),
             NodeKind::While => Some(Category::Keyword),
             NodeKind::For => Some(Category::Keyword),
             NodeKind::In => Some(Category::Keyword),
+            NodeKind::As => Some(Category::Keyword),
             NodeKind::Break => Some(Category::Keyword),
             NodeKind::Continue => Some(Category::Keyword),
             NodeKind::Return => Some(Category::Keyword),
@@ -211,6 +214,8 @@ impl Category {
             NodeKind::WithExpr => None,
             NodeKind::LetExpr => None,
             NodeKind::SetExpr => None,
+            NodeKind::ShowExpr => None,
+            NodeKind::WrapExpr => None,
             NodeKind::IfExpr => None,
             NodeKind::WhileExpr => None,
             NodeKind::ForExpr => None,
diff --git a/src/syntax/mod.rs b/src/syntax/mod.rs
index 3a0f3a5e..74a642ca 100644
--- a/src/syntax/mod.rs
+++ b/src/syntax/mod.rs
@@ -550,6 +550,10 @@ pub enum NodeKind {
     Let,
     /// The `set` keyword.
     Set,
+    /// The `show` keyword.
+    Show,
+    /// The `wrap` keyword.
+    Wrap,
     /// The `if` keyword.
     If,
     /// The `else` keyword.
@@ -572,6 +576,8 @@ pub enum NodeKind {
     Include,
     /// The `from` keyword.
     From,
+    /// The `as` keyword.
+    As,
     /// Template markup of which all lines must start in some column.
     Markup(usize),
     /// One or more whitespace characters.
@@ -665,6 +671,10 @@ pub enum NodeKind {
     LetExpr,
     /// A set expression: `set text(...)`.
     SetExpr,
+    /// A show expression: `show heading(body) as [*{body}*]`.
+    ShowExpr,
+    /// A wrap expression: `wrap body in columns(2, body)`.
+    WrapExpr,
     /// An if-else expression: `if x { y } else { z }`.
     IfExpr,
     /// A while loop expression: `while x { ... }`.
@@ -822,10 +832,13 @@ impl NodeKind {
             Self::Auto => "`auto`",
             Self::Let => "keyword `let`",
             Self::Set => "keyword `set`",
+            Self::Show => "keyword `show`",
+            Self::Wrap => "keyword `wrap`",
             Self::If => "keyword `if`",
             Self::Else => "keyword `else`",
             Self::For => "keyword `for`",
             Self::In => "keyword `in`",
+            Self::As => "keyword `as`",
             Self::While => "keyword `while`",
             Self::Break => "keyword `break`",
             Self::Continue => "keyword `continue`",
@@ -875,6 +888,8 @@ impl NodeKind {
             Self::WithExpr => "`with` expression",
             Self::LetExpr => "`let` expression",
             Self::SetExpr => "`set` expression",
+            Self::ShowExpr => "`show` expression",
+            Self::WrapExpr => "`wrap` expression",
             Self::IfExpr => "`if` expression",
             Self::WhileExpr => "while-loop expression",
             Self::ForExpr => "for-loop expression",
diff --git a/src/syntax/pretty.rs b/src/syntax/pretty.rs
index 4a05755f..f8285f0c 100644
--- a/src/syntax/pretty.rs
+++ b/src/syntax/pretty.rs
@@ -227,6 +227,8 @@ impl Pretty for Expr {
             Self::With(v) => v.pretty(p),
             Self::Let(v) => v.pretty(p),
             Self::Set(v) => v.pretty(p),
+            Self::Show(v) => v.pretty(p),
+            Self::Wrap(v) => v.pretty(p),
             Self::If(v) => v.pretty(p),
             Self::While(v) => v.pretty(p),
             Self::For(v) => v.pretty(p),
@@ -456,6 +458,24 @@ impl Pretty for SetExpr {
     }
 }
 
+impl Pretty for ShowExpr {
+    fn pretty(&self, p: &mut Printer) {
+        p.push_str("show ");
+        self.pattern().pretty(p);
+        p.push_str(" as ");
+        self.body().pretty(p);
+    }
+}
+
+impl Pretty for WrapExpr {
+    fn pretty(&self, p: &mut Printer) {
+        p.push_str("wrap ");
+        self.binding().pretty(p);
+        p.push_str(" in ");
+        self.body().pretty(p);
+    }
+}
+
 impl Pretty for IfExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("if ");
@@ -652,6 +672,8 @@ mod tests {
         roundtrip("#let x = 1 + 2");
         roundtrip("#let f(x) = y");
         roundtrip("#set text(size: 12pt)");
+        roundtrip("#show heading(body) as [*{body}*]");
+        roundtrip("#wrap body in columns(2, body)");
         roundtrip("#if x [y] else [z]");
         roundtrip("#if x {} else if y {} else {}");
         roundtrip("#while x {y}");