Added referencing using labels

README.md

@@ -4,10 +4,19 @@ An implementation of numbered theorem environments in
 [typst](https://github.com/typst/typst).
 Copy and import the [theorems.typ](theorems.typ) file to use in your own projects.
 
+### Features
+- Numbered theorem environments can be created and customized.
+- Environment counters can be _attached_ (just as subheadings are attached to headings) to other environments, headings, or keep a global count.
+- Environment numbers can be referenced, via `#thmref(<label>)`.
+ Currently, the `<label>` must be placed _inside_ the environment.
+
+## Examples
+
 Minimal example below; also see [example.typ](example.typ) ([render](example.pdf)) for a demonstration of more features, and [differential_calculus.typ](differential_calculus.typ) ([render](differential_calculus.pdf)) for a practical use case.
 
 ![basic example](basic.png)
 
+### Preamble
 ```
 #import "theorems.typ": *
 
@@ -21,7 +30,7 @@ Minimal example below; also see [example.typ](example.typ) ([render](example.pdf
   base: "theorem",
   titlefmt: strong
 )
-#let definition = thmbox("definition", "Definition")
+#let definition = thmbox("definition", "Definition", inset: (x: 1.2em, top: 1em))
 
 #let example = thmplain("example", "Example").with(numbering: none)
 #let proof = thmplain(
@@ -30,15 +39,21 @@ Minimal example below; also see [example.typ](example.typ) ([render](example.pdf
   base: "theorem",
   bodyfmt: body => [#body #h(1fr) $square$]
 ).with(numbering: none)
+```
 
-
+### Document
+```
 = Prime numbers
 
 #definition[
   A natural number is called a _prime number_ if it is greater than 1
   and cannot be written as the product of two smaller natural numbers.
 ]
-#example[The numbers $2$, $3$, and $17$ are prime.]
+#example[
+  The numbers $2$, $3$, and $17$ are prime.
+  Corollary #thmref(<cor_largest_prime>) shows that this list is not
+  exhaustive!
+]
 
 #theorem(name: "Euclid")[
   There are infinitely many primes.
@@ -51,7 +66,12 @@ Minimal example below; also see [example.typ](example.typ) ([render](example.pdf
   contradiction.
 ]
 
-#corollary[There is no largest prime number.]
-#corollary[There are infinitely many composite numbers.]
+#corollary[
+	There is no largest prime number. <cor_largest_prime>
+]
+#corollary[
+  There are infinitely many composite numbers.
+]
+
 ```
 

basic.typ

@@ -11,7 +11,7 @@
   base: "theorem",
   titlefmt: strong
 )
-#let definition = thmbox("definition", "Definition")
+#let definition = thmbox("definition", "Definition", inset: (x: 1.2em, top: 1em))
 
 #let example = thmplain("example", "Example").with(numbering: none)
 #let proof = thmplain(
@@ -30,6 +30,8 @@
 ]
 #example[
   The numbers $2$, $3$, and $17$ are prime.
+  Corollary #thmref(<cor_largest_prime>) shows that this list is not
+  exhaustive!
 ]
 
 #theorem(name: "Euclid")[
@@ -44,7 +46,7 @@
 ]
 
 #corollary[
-  There is no largest prime number.
+  There is no largest prime number. <cor_largest_prime>
 ]
 #corollary[
   There are infinitely many composite numbers.

example.typ

@@ -91,7 +91,11 @@
 ]
 
 #corollary[#lorem(4)]
-#corollary[#lorem(8)]
+#corollary[
+  This corollary will be referenced later, in
+  Lemma #thmref(<lemref>).    // Reference future lemma
+  <corref>    // Label this corollary
+]
 
 #example[#lorem(10)]
 
@@ -105,7 +109,7 @@
 #notation[#lorem(7)]
 
 #example(name: [#lorem(3)])[#lorem(10)]
-#remark[#lorem(5)]
+#remark[#lorem(8)]
 
 #theorem[#lorem(6)]
 
@@ -114,10 +118,15 @@
 #proof(numbering: "1.1")[#lorem(5)]
 
 = Heading
-#lemma[#lorem(14)]
+#lemma[
+  #lorem(14)
+  Refer to Corollary #thmref(<corref>). <lemref>
+]
 #remark[#lorem(8)]
 
-#corollary(name: [#lorem(4)])[#lorem(12)]
+#corollary(name: [#lorem(4)])[
+  #lorem(12) <myref>
+]
 // The base can be overridden
 #example(numbering: "1.1.1.a", base: "corollary")[#lorem(20)]
 #example(numbering: "1.1.1.a", base: "corollary")[#lorem(10)]

theorems.typ

@@ -1,3 +1,12 @@
+// Store theorem environment numbering
+
+#let thmcounters = state("thm",
+  (
+    "counters": ("": (), "heading": ()),
+    "latest": ()
+  )
+)
+
 // Create a theorem environment with counter identified by "identifier",
 // attached to environments with identifier "base". Contents are formatted
 // using "fmt", which maps (name, number, body) to content.
@@ -13,13 +22,6 @@
 
 #let thmenv(identifier, base, fmt) = {
 
-  let thmcounters = state("thm",
-    (
-      "counters": ("": (), "heading": ()),
-      "latest": ()
-    )
-  )
-
   let global_numbering = numbering
 
   return (body, name: none, numbering: "1.1", base: base) => {
@@ -59,6 +61,22 @@
 }
 
 
+// Reference a theorem with a <label> _inside_ it, using #thmref(<label>).
+// Optionally supply a "fmt" function to change the display style.
+
+#let thmref(label, fmt: nums => numbering("1.1", ..nums)) = {
+  locate(loc => {
+    let elements = query(label, loc)
+    assert(elements.len() > 0, message: "Label not found!")
+    assert(elements.len() == 1, message: "Multiple labels found!")
+    let number = thmcounters.at(
+      elements.first().location()
+    ).at("latest")
+    return fmt(number)
+  })
+}
+
+
 // Creates a box-like theorem environment with parameters "identifier" and "base" (defaulted to "heading").
 //    head          indicates the name of the environment appearing in the title
 //    namefmt:      formatting to apply to the "name", defaults to wrapping in parentheses