fix: handle latex equations when rendering typst

src/export/site.rs

@@ -941,20 +941,29 @@ items:
         let rec = record();
         let frags = solution_fragments(&cat, &rec, &form()).unwrap();
         let open = &frags.iter().find(|(id, _)| id == "q-open").unwrap().1;
-        assert!(open.contains("<div class=\"sol-model\">"), "model answer shown:\n{open}");
+        assert!(
+            open.contains("<div class=\"sol-model\">"),
+            "model answer shown:\n{open}"
+        );
         assert_eq!(
             open.matches("<p class=\"sol-explain\">").count(),
             2,
             "each explanation paragraph is its own styled <p>:\n{open}"
         );
-        assert!(open.contains("folded into H"), "first paragraph present:\n{open}");
+        assert!(
+            open.contains("folded into H"),
+            "first paragraph present:\n{open}"
+        );
         assert!(
             open.contains("reads the enthalpy change directly"),
             "second paragraph present:\n{open}"
         );
         let model_at = open.find("sol-model").unwrap();
         let explain_at = open.find("sol-explain").unwrap();
-        assert!(model_at < explain_at, "model answer comes before the explanation");
+        assert!(
+            model_at < explain_at,
+            "model answer comes before the explanation"
+        );
     }
 
     #[test]

src/export/typst/config.rs

@@ -607,6 +607,8 @@ defaults:
   extra:
     accent: '#017ab9'
     font: 'Libertinus Serif'
+    show-bubbles: true
+    bubble-radius: '0.42em'
 
 variants:
   exam:

src/export/typst/payload.rs

@@ -1070,8 +1070,61 @@ fn numeric_map(map: &BTreeMap<String, f64>) -> Value {
     )
 }
 
-/// Emits authored markup as either a content block or a quoted string.
+/// Rewrites inline LaTeX math (`$...$`) into a call to mitex's `mi`, so Typst's
+/// own math grammar never has to parse it. Typst's `\times`, `\Delta`, `\ln` and
+/// friends are not valid Typst math — a bare backslash escapes the next
+/// character instead of naming a symbol — which is why equations compile but
+/// print wrong instead of failing outright. `\$` is left alone, matching LaTeX's
+/// own convention for a literal dollar sign, and a `$` with no matching close is
+/// left alone too, rather than swallowing the rest of the field.
+fn rewrite_latex_math(source: &str) -> String {
+    let chars: Vec<(usize, char)> = source.char_indices().collect();
+    let mut out = String::with_capacity(source.len());
+    let mut i = 0;
+    while i < chars.len() {
+        let (_, c) = chars[i];
+        if c == '\\' && i + 1 < chars.len() {
+            out.push('\\');
+            out.push(chars[i + 1].1);
+            i += 2;
+            continue;
+        }
+        if c != '$' {
+            out.push(c);
+            i += 1;
+            continue;
+        }
+        let mut j = i + 1;
+        let close = loop {
+            if j >= chars.len() {
+                break None;
+            }
+            match chars[j].1 {
+                '\\' => j += 2,
+                '$' => break Some(j),
+                _ => j += 1,
+            }
+        };
+        match close {
+            Some(close_idx) => {
+                let start = chars[i + 1].0;
+                let end = chars[close_idx].0;
+                out.push_str("#mi(");
+                out.push_str(&Value::str(&source[start..end]).to_typst(0));
+                out.push(')');
+                i = close_idx + 1;
+            }
+            None => {
+                out.push('$');
+                i += 1;
+            }
+        }
+    }
+    out
+}
+
 fn markup_value(source: &str, content: bool) -> Value {
+    let source = rewrite_latex_math(source);
     if content {
         Value::content(source)
     } else {
@@ -1221,3 +1274,17 @@ mod tests {
         assert!(!balanced("closing ] first"));
     }
 }
+
+#[test]
+fn latex_math_becomes_a_mitex_call() {
+    assert_eq!(
+        rewrite_latex_math("angle $\\phi$ (phi)"),
+        "angle #mi(\"\\\\phi\") (phi)"
+    );
+}
+
+#[test]
+fn escaped_and_unmatched_dollar_signs_are_left_alone() {
+    assert_eq!(rewrite_latex_math("costs \\$5 total"), "costs \\$5 total");
+    assert_eq!(rewrite_latex_math("just $5"), "just $5");
+}

src/export/typst/templates/answer-sheet.typ

@@ -12,6 +12,8 @@
 // templates/typst.yaml under `extra` rather than editing the geometry here, and
 // check one printed page against your scanner before running a class through it.
 
+#import "@preview/mitex:0.2.7": mi
+
 // coursebank:begin data
 #let cb-data = (
   course: (code: "COURSE 101", title: "Sample Course", term: "2026s"),

src/export/typst/templates/exam.typ

@@ -24,6 +24,8 @@
 // copy — export the `key` variant instead, or the day you forget an `if` is the
 // day the class gets the answers.
 
+#import "@preview/mitex:0.2.7": mi
+
 // ─────────────────────────────────────────────────────────────────────────────
 // Metadata
 // ─────────────────────────────────────────────────────────────────────────────
@@ -52,12 +54,14 @@
 // how a course changes the look without editing this file at all.
 #let extra = cb-meta.at("extra", default: (:))
 #let accent = rgb(extra.at("accent", default: "#1f4e79"))
-#let body-font = extra.at("font", default: "Libertinus Serif")
+#let body-font = extra.at("font", default: "Roboto")
 #let body-size = eval(extra.at("font-size", default: "11pt"))
 #let paper = extra.at("paper", default: "us-letter")
 #let show-name-block = extra.at("name-block", default: true)
 #let show-points = extra.at("show-points", default: true)
 #let page-per-item = extra.at("page-per-item", default: false)
+#let show-bubbles = extra.at("show-bubbles", default: true)
+#let bubble-radius = eval(extra.at("bubble-radius", default: "0.42em"))
 
 #let form-note = if cb-meta.form.at("count", default: 1) > 1 {
   " · Form " + cb-meta.form.id
@@ -120,6 +124,11 @@
   }
 }
 
+// An unfilled bubble a student marks by hand. `bubble-radius` is the same knob
+// the standalone answer sheet reads, so the two stay visually consistent if you
+// ever generate both.
+#let bubble() = circle(radius: bubble-radius, stroke: 0.5pt)
+
 // ─────────────────────────────────────────────────────────────────────────────
 // The renderer
 // ─────────────────────────────────────────────────────────────────────────────
@@ -154,11 +163,19 @@
 
   block(inset: (left: 1.2em))[
     #for opt in q.at("options", default: ()) {
-      grid(
-        columns: (1.4em, 1fr),
-        gutter: 0.2em,
-        [#(opt.letter + ".")], [#markup(opt.text)],
-      )
+      if show-bubbles {
+        grid(
+          columns: (1.6em, 1.4em, 1fr),
+          gutter: 0.2em,
+          align(horizon)[#bubble()], [#(opt.letter + ".")], [#markup(opt.text)],
+        )
+      } else {
+        grid(
+          columns: (1.4em, 1fr),
+          gutter: 0.2em,
+          [#(opt.letter + ".")], [#markup(opt.text)],
+        )
+      }
       v(0.15em)
     }
   ]

src/export/typst/templates/key.typ

@@ -13,6 +13,8 @@
 // paper's config, and it is why these are two templates rather than one with a
 // flag.
 
+#import "@preview/mitex:0.2.7": mi
+
 // coursebank:begin data
 #let cb-data = (
   course: (code: "COURSE 101", title: "Sample Course", term: "2026s"),

src/util/markup.rs

@@ -139,10 +139,25 @@ pub fn to_markdown(src: &str) -> String {
         .to_string()
 }
 
-/// Passes authoring markup through for Typst.
+/// Passes authoring markup through for Typst, translating inline LaTeX math on
+/// the way.
 ///
-/// The markup is already a Typst subset, so this only normalizes whitespace and
-/// escapes the few characters Typst treats specially in content mode.
+/// Outside math this only escapes the characters Typst treats specially in
+/// content mode: a bare `@` or `<` starts a reference or label.
+///
+/// Math is different. Authors write ordinary LaTeX between `$...$`, and Typst's
+/// own math grammar is not LaTeX's — a backslash escapes the next character
+/// rather than naming a symbol, so `\Delta`, `\times`, `\ln` compile without
+/// error and print wrong. Each `$...$` span is instead handed whole to
+/// mitex's `mi`, which parses LaTeX grammar on purpose: `$\phi$` becomes
+/// `#mi("\\phi")`. The `@`/`<`/`>` escaping above is skipped for anything
+/// inside the span, since it reaches Typst as a string argument, not as
+/// markup — escaping `<` there would corrupt the LaTeX rather than protect
+/// anything.
+///
+/// `\$` is left alone, matching LaTeX's own convention for a literal dollar
+/// sign. A `$` with no matching close is escaped the same way rather than left
+/// to open Typst's own math mode on a stray price or a malformed source line.
 ///
 /// # Arguments
 ///
@@ -152,17 +167,84 @@ pub fn to_markdown(src: &str) -> String {
 ///
 /// Typst content-mode markup.
 pub fn to_typst(src: &str) -> String {
+    let src = src.trim();
+    let chars: Vec<(usize, char)> = src.char_indices().collect();
     let mut out = String::with_capacity(src.len());
-    for ch in src.trim().chars() {
-        match ch {
-            // A bare `@` or `<` starts a Typst reference or label.
+    let mut i = 0;
+    while i < chars.len() {
+        let (_, c) = chars[i];
+
+        // An escaped pair is copied verbatim and never reconsidered, so `\$`
+        // can't be mistaken for the start of math and an `\@`/`\<`/`\>` an
+        // author already wrote is not escaped a second time.
+        if c == '\\' && i + 1 < chars.len() {
+            out.push('\\');
+            out.push(chars[i + 1].1);
+            i += 2;
+            continue;
+        }
+
+        if c == '$' {
+            match find_math_close(&chars, i) {
+                Some(close) => {
+                    let start = chars[i + 1].0;
+                    let end = chars[close].0;
+                    out.push_str("#mi(");
+                    push_typst_string(&mut out, &src[start..end]);
+                    out.push(')');
+                    i = close + 1;
+                    continue;
+                }
+                None => {
+                    out.push_str("\\$");
+                    i += 1;
+                    continue;
+                }
+            }
+        }
+
+        match c {
             '@' => out.push_str("\\@"),
             '<' => out.push_str("\\<"),
             '>' => out.push_str("\\>"),
+            _ => out.push(c),
+        }
+        i += 1;
+    }
+    out
+}
+
+/// Finds the index into `chars` of the `$` matching the opener at `open`. A
+/// backslash-escaped pair is skipped as a unit, so a `\$` inside the math span
+/// doesn't close it early.
+fn find_math_close(chars: &[(usize, char)], open: usize) -> Option<usize> {
+    let mut j = open + 1;
+    while j < chars.len() {
+        match chars[j].1 {
+            '\\' if j + 1 < chars.len() => j += 2,
+            '$' => return Some(j),
+            _ => j += 1,
+        }
+    }
+    None
+}
+
+/// Writes `s` as a quoted Typst string. Kept local, duplicating the five-case
+/// match in `typst::value::write_string`, rather than reaching into the
+/// Typst-specific value writer for one small helper.
+fn push_typst_string(out: &mut String, s: &str) {
+    out.push('"');
+    for ch in s.chars() {
+        match ch {
+            '"' => out.push_str("\\\""),
+            '\\' => out.push_str("\\\\"),
+            '\n' => out.push_str("\\n"),
+            '\r' => out.push_str("\\r"),
+            '\t' => out.push_str("\\t"),
             _ => out.push(ch),
         }
     }
-    out
+    out.push('"');
 }
 
 /// Escapes the five XML-significant characters.
@@ -423,3 +505,27 @@ mod tests {
         assert_eq!(to_markdown("one\n\ntwo"), "one\n\ntwo");
     }
 }
+
+#[test]
+fn latex_math_becomes_a_mitex_call() {
+    assert_eq!(
+        to_typst("angle $\\phi$ (phi)"),
+        "angle #mi(\"\\\\phi\") (phi)"
+    );
+}
+
+#[test]
+fn comparison_operators_inside_math_are_not_escaped() {
+    assert_eq!(to_typst("$\\Delta H < 0$"), "#mi(\"\\\\Delta H < 0\")");
+}
+
+#[test]
+fn reference_starters_outside_math_are_still_escaped() {
+    assert_eq!(to_typst("see @fig:x and x < y"), "see \\@fig:x and x \\< y");
+}
+
+#[test]
+fn escaped_and_unmatched_dollar_signs_are_left_or_escaped() {
+    assert_eq!(to_typst("costs \\$5 total"), "costs \\$5 total");
+    assert_eq!(to_typst("just $5"), "just \\$5");
+}