style(show): use show: lettre.with() instead of unnamed function

- Maybe more idiomatic… not sure actually

exemple.typ

@@ -0,0 +1,30 @@
+#import "lettre.typ": *
+#show link: strong
+
+#show: lettre.with(
+  de: [
+    Ex Péditeur,\
+    12 rue des Sept Nains\
+    12340, Bozouls, France
+  ],
+  pour: [
+    Dest I’nataire,\
+    77 avenue du Moulin,\
+    56780, Île aux Moines, Bretagne
+  ],
+  objet: "Attestation sur l’honneur",
+  date: "10 septembre 2024",
+  lieu: "Bozouls",
+  introduction: "Monsieur",
+  cloture: "Cordialement,",
+  signature: "Ex P.",
+  post: [
+    #emph("PS: Finalement, rien.")
+  ],
+)
+
+je soussigné, Ex Péditeur, atteste par la présente sur l’honneur que ce document
+a été réalisé avec #link("https://typst.app/")[Typst].
+
+Les sources sont disponibles à l’adresse suivante:
+#link("https://git.epheme.re/fmouhart/typst-lettre").

lettre.typ

@@ -0,0 +1,63 @@
+#let lettre(
+  de: "",
+  pour: "",
+  objet: "",
+  date: "",
+  lieu: "",
+  introduction: "",
+  cloture: "",
+  signature: "",
+  post: "",
+  doc
+) = {
+  set page(margin: 1.5in)
+  set par(leading: 0.55em, first-line-indent: 2em, justify: true, spacing: 0.55em)
+  set text(font: "Libertinus Serif", size: 12pt)
+  set document(title: objet, author: signature)
+  show raw: set text(font: "Inconsolata")
+  show heading: set block(above: 1.4em, below: 1em)
+
+  let formatLieuDate(lieu, date) = {
+    let isDate = date.trim().len() > 0;
+    let isLieu = lieu.trim().len() > 0;
+    if isLieu [#lieu]
+    if isDate {
+      if isLieu [, ]
+      [le #date]
+    }
+  }
+
+  grid(
+    columns: (2fr, 1fr, 2fr),
+    par(de),
+    text[],
+    text[
+      #formatLieuDate(lieu, date)
+    ] + v(2em),
+    text[],
+    text[],
+    par(pour)
+  )
+  v(1em)
+  if objet.trim().len() > 0 {
+    heading(level: 3, text("Objet: " + objet))
+    v(1em)
+  }
+  par(first-line-indent: 0pt, text(introduction + ","))
+  v(1em)
+  doc
+  v(1em)
+  par(first-line-indent: 0pt, text(cloture))
+  v(.7em)
+  grid(
+    columns: (2fr, 1fr),
+    text[],
+    text(signature)
+  )
+  v(1em)
+  post
+}
+
+#let er = [#super[er]]
+#let ème = [#super[ème]]
+#let no(num) = { text([n°~] + num) }

readme.md

@@ -1 +1,40 @@
 A simple template for French letters for typst.
+
+## Usage
+
+To create a letter, write a typst document while defining the following
+parameters, with the [`lettre.typ`](./lettre.typ) file in the same folder:
+
+```typst
+#import "lettre.typ": *
+
+#show: lettre.with(
+  de: [
+    Sender\
+    Address
+  ],
+  pour: [
+    Recipient\
+    Address
+  ],
+  objet: "subject of the letter", // optional
+  date: "date of sending", // optional
+  lieu: "location", // optional
+  introduction: "opening",
+  cloture: "closing",
+  signature: "signature",
+  post: [
+    post-letter (e.g., post-scriptum)
+  ],
+)
+```
+
+Now you can fill the letter afterward, and compile your document with:
+
+```bash
+typst compile <filename.typ>
+```
+
+## Example
+
+An example file is given in the [`exemple.typ`](./exemple.typ) file in the repository.