Math delimiter grouping

9 files changed, 204 insertions, 28 deletions

diff --git a/library/src/lib.rs b/library/src/lib.rs
index f714c72b..c2f51ee4 100644
--- a/library/src/lib.rs
+++ b/library/src/lib.rs
@@ -189,6 +189,7 @@ fn items() -> LangItems {
         },
         math: |body, block| math::MathNode { body, block }.pack(),
         math_atom: |atom| math::AtomNode(atom).pack(),
+        math_delimited: |body| math::LrNode(body).pack(),
         math_script: |base, sub, sup| math::ScriptNode { base, sub, sup }.pack(),
         math_frac: |num, denom| math::FracNode { num, denom }.pack(),
         math_align_point: || math::AlignPointNode.pack(),
diff --git a/library/src/math/lr.rs b/library/src/math/lr.rs
new file mode 100644
index 00000000..9cfc6e5f
--- /dev/null
+++ b/library/src/math/lr.rs
@@ -0,0 +1,78 @@
+use super::*;
+
+/// How much less high scaled delimiters can be than what they wrap.
+const DELIM_SHORT_FALL: Em = Em::new(0.1);
+
+/// # Left-Right
+/// Scales delimiters.
+///
+/// While matched delimiters scale by default, this can be used to scale
+/// unmatched delimiters and to control the delimiter scaling more precisely.
+///
+/// ## Example
+/// ```
+/// $ lr(]a, b/2]) $
+/// ```
+///
+/// ## Parameters
+/// - body: Content (positional, variadic)
+///   The delimited content, including the delimiters.
+///
+/// ## Category
+/// math
+#[func]
+#[capable(LayoutMath)]
+#[derive(Debug, Hash)]
+pub struct LrNode(pub Content);
+
+#[node]
+impl LrNode {
+    fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
+        let mut body = Content::empty();
+        for (i, arg) in args.all::<Content>()?.into_iter().enumerate() {
+            if i > 0 {
+                body += AtomNode(','.into()).pack();
+            }
+            body += arg;
+        }
+        Ok(Self(body).pack())
+    }
+}
+
+impl LayoutMath for LrNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        let mut row = ctx.layout_row(&self.0)?;
+
+        let axis = scaled!(ctx, axis_height);
+        let max_extent = row
+            .0
+            .iter()
+            .map(|fragment| (fragment.ascent() - axis).max(fragment.descent() + axis))
+            .max()
+            .unwrap_or_default();
+
+        let height = 2.0 * max_extent;
+        if let [first, .., last] = row.0.as_mut_slice() {
+            for fragment in [first, last] {
+                if !matches!(
+                    fragment.class(),
+                    Some(MathClass::Opening | MathClass::Closing | MathClass::Fence)
+                ) {
+                    continue;
+                }
+
+                let MathFragment::Glyph(glyph) = *fragment else { continue };
+                let short_fall = DELIM_SHORT_FALL.at(glyph.font_size);
+                *fragment = MathFragment::Variant(
+                    glyph.stretch_vertical(ctx, height, short_fall),
+                );
+            }
+        }
+
+        for fragment in row.0 {
+            ctx.push(fragment);
+        }
+
+        Ok(())
+    }
+}
diff --git a/library/src/math/mod.rs b/library/src/math/mod.rs
index ae660405..44b52e96 100644
--- a/library/src/math/mod.rs
+++ b/library/src/math/mod.rs
@@ -8,6 +8,7 @@ mod atom;
 mod braced;
 mod frac;
 mod fragment;
+mod lr;
 mod matrix;
 mod op;
 mod root;
@@ -50,6 +51,7 @@ use crate::text::{families, variant, FallbackList, FontFamily, SpaceNode, Symbol
 /// Hook up all math definitions.
 pub fn define(scope: &mut Scope) {
     scope.def_func::<MathNode>("math");
+    scope.def_func::<LrNode>("lr");
     scope.def_func::<AccentNode>("accent");
     scope.def_func::<FracNode>("frac");
     scope.def_func::<BinomNode>("binom");
diff --git a/src/ide/highlight.rs b/src/ide/highlight.rs
index 42c05002..5f615d04 100644
--- a/src/ide/highlight.rs
+++ b/src/ide/highlight.rs
@@ -115,6 +115,7 @@ pub fn highlight(node: &LinkedNode) -> Option<Category> {
         SyntaxKind::TermMarker => Some(Category::ListMarker),
         SyntaxKind::Math => None,
         SyntaxKind::Atom => None,
+        SyntaxKind::Delimited => None,
         SyntaxKind::Script => None,
         SyntaxKind::Frac => None,
         SyntaxKind::AlignPoint => Some(Category::MathOperator),
diff --git a/src/model/eval.rs b/src/model/eval.rs
index b037a1bd..91112949 100644
--- a/src/model/eval.rs
+++ b/src/model/eval.rs
@@ -280,6 +280,7 @@ impl Eval for ast::Expr {
             Self::Enum(v) => v.eval(vm).map(Value::Content),
             Self::Term(v) => v.eval(vm).map(Value::Content),
             Self::Atom(v) => v.eval(vm).map(Value::Content),
+            Self::Delimited(v) => v.eval(vm).map(Value::Content),
             Self::Script(v) => v.eval(vm).map(Value::Content),
             Self::Frac(v) => v.eval(vm).map(Value::Content),
             Self::AlignPoint(v) => v.eval(vm).map(Value::Content),
@@ -325,10 +326,19 @@ impl ast::Expr {
             Self::Shorthand(v) => v.eval_in_math(vm)?,
             Self::Symbol(v) => v.eval_in_math(vm)?,
             Self::Ident(v) => v.eval_in_math(vm)?,
+            Self::FuncCall(v) => v.eval_in_math(vm)?,
             _ => self.eval(vm)?.display_in_math(),
         }
         .spanned(self.span()))
     }
+
+    fn eval_without_parens(&self, vm: &mut Vm) -> SourceResult<Content> {
+        Ok(match self {
+            Self::Delimited(v) => v.eval_without_parens(vm)?,
+            _ => self.eval_in_math(vm)?,
+        }
+        .spanned(self.span()))
+    }
 }
 
 impl Eval for ast::Text {
@@ -401,7 +411,7 @@ impl Eval for ast::Symbol {
 
 impl ast::Symbol {
     fn eval_in_math(&self, vm: &mut Vm) -> SourceResult<Content> {
-        Ok((vm.items.symbol)(EcoString::from(self.get()) + ":op".into()))
+        Ok((vm.items.symbol)(EcoString::from(self.get()) + ":op:square".into()))
     }
 }
 
@@ -511,7 +521,7 @@ impl Eval for ast::Math {
             .map(|expr| expr.eval_in_math(vm))
             .collect::<SourceResult<_>>()?;
         let block = self.block();
-        Ok((vm.items.math)(seq, block))
+        Ok((vm.items.math)(Content::sequence(seq), block))
     }
 }
 
@@ -523,13 +533,44 @@ impl Eval for ast::Atom {
     }
 }
 
+impl Eval for ast::Delimited {
+    type Output = Content;
+
+    fn eval(&self, vm: &mut Vm) -> SourceResult<Self::Output> {
+        let seq = self
+            .exprs()
+            .map(|expr| expr.eval_in_math(vm))
+            .collect::<SourceResult<_>>()?;
+        Ok((vm.items.math_delimited)(Content::sequence(seq)))
+    }
+}
+
+impl ast::Delimited {
+    fn eval_without_parens(&self, vm: &mut Vm) -> SourceResult<Content> {
+        let exprs: Vec<_> = self.exprs().collect();
+        let mut slice = exprs.as_slice();
+        if let (Some(ast::Expr::Atom(first)), Some(ast::Expr::Atom(last))) =
+            (exprs.first(), exprs.last())
+        {
+            if first.get() == "(" && last.get() == ")" {
+                slice = &exprs[1..exprs.len() - 1];
+            }
+        }
+        let seq = slice
+            .iter()
+            .map(|expr| expr.eval_in_math(vm))
+            .collect::<SourceResult<_>>()?;
+        Ok((vm.items.math_delimited)(Content::sequence(seq)))
+    }
+}
+
 impl Eval for ast::Script {
     type Output = Content;
 
     fn eval(&self, vm: &mut Vm) -> SourceResult<Self::Output> {
         let base = self.base().eval_in_math(vm)?;
-        let sub = self.sub().map(|expr| expr.eval_in_math(vm)).transpose()?;
-        let sup = self.sup().map(|expr| expr.eval_in_math(vm)).transpose()?;
+        let sub = self.sub().map(|expr| expr.eval_without_parens(vm)).transpose()?;
+        let sup = self.sup().map(|expr| expr.eval_without_parens(vm)).transpose()?;
         Ok((vm.items.math_script)(base, sub, sup))
     }
 }
@@ -538,8 +579,8 @@ impl Eval for ast::Frac {
     type Output = Content;
 
     fn eval(&self, vm: &mut Vm) -> SourceResult<Self::Output> {
-        let num = self.num().eval_in_math(vm)?;
-        let denom = self.denom().eval_in_math(vm)?;
+        let num = self.num().eval_without_parens(vm)?;
+        let denom = self.denom().eval_without_parens(vm)?;
         Ok((vm.items.math_frac)(num, denom))
     }
 }
@@ -878,12 +919,29 @@ impl Eval for ast::FuncCall {
     type Output = Value;
 
     fn eval(&self, vm: &mut Vm) -> SourceResult<Self::Output> {
+        let callee = self.callee();
+        let callee = callee.eval(vm)?.cast::<Func>().at(callee.span())?;
+        self.eval_with_callee(vm, callee)
+    }
+}
+
+impl ast::FuncCall {
+    fn eval_in_math(&self, vm: &mut Vm) -> SourceResult<Content> {
+        let callee = self.callee().eval(vm)?;
+        if let Value::Func(callee) = callee {
+            Ok(self.eval_with_callee(vm, callee)?.display_in_math())
+        } else {
+            Ok(callee.display_in_math()
+                + (vm.items.math_atom)("(".into())
+                + (vm.items.math_atom)(")".into()))
+        }
+    }
+
+    fn eval_with_callee(&self, vm: &mut Vm, callee: Func) -> SourceResult<Value> {
         if vm.depth >= MAX_CALL_DEPTH {
             bail!(self.span(), "maximum function call depth exceeded");
         }
 
-        let callee = self.callee();
-        let callee = callee.eval(vm)?.cast::<Func>().at(callee.span())?;
         let args = self.args().eval(vm)?;
         let point = || Tracepoint::Call(callee.name().map(Into::into));
         callee.call(vm, args).trace(vm.world, point, self.span())
diff --git a/src/model/library.rs b/src/model/library.rs
index 96218bb1..54eeeb5b 100644
--- a/src/model/library.rs
+++ b/src/model/library.rs
@@ -66,7 +66,10 @@ pub struct LangItems {
     /// An item in a term list: `/ Term: Details`.
     pub term_item: fn(term: Content, description: Content) -> Content,
     /// A mathematical formula: `$x$`, `$ x^2 $`.
-    pub math: fn(children: Vec<Content>, block: bool) -> Content,
+    pub math: fn(body: Content, block: bool) -> Content,
+    /// A subsection in a math formula that is surrounded by matched delimiters:
+    /// `[x + y]`.
+    pub math_delimited: fn(body: Content) -> Content,
     /// An atom in a formula: `x`, `+`, `12`.
     pub math_atom: fn(atom: EcoString) -> Content,
     /// A base with optional sub- and superscripts in a formula: `a_1^2`.
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index d70c4ae4..ceda2d57 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -117,6 +117,9 @@ pub enum Expr {
     Math(Math),
     /// An atom in a math formula: `x`, `+`, `12`.
     Atom(Atom),
+    /// A subsection in a math formula that is surrounded by matched delimiters:
+    /// `[x + y]`.
+    Delimited(Delimited),
     /// A base with optional sub- and superscripts in a math formula: `a_1^2`.
     Script(Script),
     /// A fraction in a math formula: `x/2`.
@@ -216,6 +219,7 @@ impl AstNode for Expr {
             SyntaxKind::TermItem => node.cast().map(Self::Term),
             SyntaxKind::Math => node.cast().map(Self::Math),
             SyntaxKind::Atom => node.cast().map(Self::Atom),
+            SyntaxKind::Delimited => node.cast().map(Self::Delimited),
             SyntaxKind::Script => node.cast().map(Self::Script),
             SyntaxKind::Frac => node.cast().map(Self::Frac),
             SyntaxKind::AlignPoint => node.cast().map(Self::AlignPoint),
@@ -275,6 +279,7 @@ impl AstNode for Expr {
             Self::Term(v) => v.as_untyped(),
             Self::Math(v) => v.as_untyped(),
             Self::Atom(v) => v.as_untyped(),
+            Self::Delimited(v) => v.as_untyped(),
             Self::Script(v) => v.as_untyped(),
             Self::Frac(v) => v.as_untyped(),
             Self::AlignPoint(v) => v.as_untyped(),
@@ -658,6 +663,19 @@ impl Atom {
 }
 
 node! {
+    /// A subsection in a math formula that is surrounded by matched delimiters:
+    /// `[x + y]`.
+    Delimited
+}
+
+impl Delimited {
+    /// The contents, including the delimiters.
+    pub fn exprs(&self) -> impl DoubleEndedIterator<Item = Expr> + '_ {
+        self.0.children().filter_map(Expr::cast_with_space)
+    }
+}
+
+node! {
     /// A base with an optional sub- and superscript in a formula: `a_1^2`.
     Script
 }
@@ -673,8 +691,7 @@ impl Script {
         self.0
             .children()
             .skip_while(|node| !matches!(node.kind(), SyntaxKind::Underscore))
-            .nth(1)
-            .map(|node| node.cast().expect("script node has invalid subscript"))
+            .find_map(SyntaxNode::cast)
     }
 
     /// The superscript.
@@ -682,8 +699,7 @@ impl Script {
         self.0
             .children()
             .skip_while(|node| !matches!(node.kind(), SyntaxKind::Hat))
-            .nth(1)
-            .map(|node| node.cast().expect("script node has invalid superscript"))
+            .find_map(SyntaxNode::cast)
     }
 }
 
diff --git a/src/syntax/kind.rs b/src/syntax/kind.rs
index 5928fa0a..206df911 100644
--- a/src/syntax/kind.rs
+++ b/src/syntax/kind.rs
@@ -61,6 +61,9 @@ pub enum SyntaxKind {
     Math,
     /// An atom in math: `x`, `+`, `12`.
     Atom,
+    /// A subsection in a math formula that is surrounded by matched delimiters:
+    /// `[x + y]`.
+    Delimited,
     /// A base with optional sub- and superscripts in math: `a_1^2`.
     Script,
     /// A fraction in math: `x/2`.
@@ -336,6 +339,7 @@ impl SyntaxKind {
             Self::TermItem => "term list item",
             Self::TermMarker => "term marker",
             Self::Math => "math formula",
+            Self::Delimited => "delimited math",
             Self::Atom => "math atom",
             Self::Script => "script",
             Self::Frac => "fraction",
diff --git a/src/syntax/parser.rs b/src/syntax/parser.rs
index a379500c..15839e18 100644
--- a/src/syntax/parser.rs
+++ b/src/syntax/parser.rs
@@ -1,6 +1,8 @@
 use std::collections::HashSet;
 use std::ops::Range;
 
+use unicode_math_class::MathClass;
+
 use super::{ast, is_newline, ErrorPos, LexMode, Lexer, SyntaxKind, SyntaxNode};
 use crate::util::{format_eco, EcoString};
 
@@ -233,12 +235,13 @@ fn math_expr_prec(p: &mut Parser, min_prec: usize, stop: SyntaxKind) {
             }
         }
 
-        SyntaxKind::Atom => match p.current_text() {
-            "(" => math_delimited(p, ")"),
-            "{" => math_delimited(p, "}"),
-            "[" => math_delimited(p, "]"),
-            _ => p.eat(),
-        },
+        SyntaxKind::Atom if math_class(p.current_text()) == Some(MathClass::Fence) => {
+            math_delimited(p, MathClass::Fence)
+        }
+
+        SyntaxKind::Atom if math_class(p.current_text()) == Some(MathClass::Opening) => {
+            math_delimited(p, MathClass::Closing)
+        }
 
         SyntaxKind::Let
         | SyntaxKind::Set
@@ -254,7 +257,8 @@ fn math_expr_prec(p: &mut Parser, min_prec: usize, stop: SyntaxKind) {
         | SyntaxKind::LeftBrace
         | SyntaxKind::LeftBracket => embedded_code_expr(p),
 
-        SyntaxKind::Linebreak
+        SyntaxKind::Atom
+        | SyntaxKind::Linebreak
         | SyntaxKind::Escape
         | SyntaxKind::Shorthand
         | SyntaxKind::Symbol
@@ -288,21 +292,30 @@ fn math_expr_prec(p: &mut Parser, min_prec: usize, stop: SyntaxKind) {
     }
 }
 
-fn math_delimited(p: &mut Parser, closing: &str) {
+fn math_delimited(p: &mut Parser, stop: MathClass) {
     let m = p.marker();
     p.expect(SyntaxKind::Atom);
-    while !p.eof()
-        && !p.at(SyntaxKind::Dollar)
-        && (!p.at(SyntaxKind::Atom) || p.current_text() != closing)
-    {
+    while !p.eof() && !p.at(SyntaxKind::Dollar) {
+        if math_class(p.current_text()) == Some(stop) {
+            p.eat();
+            p.wrap(m, SyntaxKind::Delimited);
+            return;
+        }
+
         let prev = p.prev_end();
         math_expr(p);
         if !p.progress(prev) {
             p.unexpected();
         }
     }
-    p.expect(SyntaxKind::Atom);
-    p.wrap(m, SyntaxKind::Math);
+}
+
+fn math_class(text: &str) -> Option<MathClass> {
+    let mut chars = text.chars();
+    chars
+        .next()
+        .filter(|_| chars.next().is_none())
+        .and_then(unicode_math_class::class)
 }
 
 fn math_op(kind: SyntaxKind) -> Option<(SyntaxKind, SyntaxKind, ast::Assoc, usize)> {
@@ -324,7 +337,7 @@ fn math_args(p: &mut Parser) {
     p.expect(SyntaxKind::Atom);
     let m = p.marker();
     let mut m2 = p.marker();
-    while !p.eof() {
+    while !p.eof() && !p.at(SyntaxKind::Dollar) {
         match p.current_text() {
             ")" => break,
             "," => {