paragraph demo

data/two-paragraphs.txt

@@ -0,0 +1,5 @@
+foo
+bar
+
+alpha
+bravo

firepower-demo/src/main/scala/com/htmlism/firepower/demo/Line.scala

@@ -1,10 +1,6 @@
 package com.htmlism.firepower.demo
 
-case class Line(s: String)
-
 object Line:
-  def mkString(xs: List[Line]): String =
+  def mkString(xs: List[String]): String =
     xs
-      .iterator
-      .map(_.s)
       .mkString("\n")

firepower-demo/src/main/scala/com/htmlism/firepower/demo/Paragraph.scala

@@ -0,0 +1,26 @@
+package com.htmlism.firepower.demo
+
+/**
+  * An abstraction for groups of lines that are eventually separated by newlines, but between paragraphs there's an
+  * extra newline
+  */
+case class Paragraph(xs: List[String])
+
+object Paragraph:
+  val blankLine: Paragraph =
+    Paragraph(List(""))
+
+  def apply(xs: String*): Paragraph =
+    Paragraph(xs.toList)
+
+  def mkLines(ps: List[Paragraph]): List[String] =
+    interlace(blankLine)(ps)
+      .flatMap(_.xs)
+
+  private def interlace[A](x: A)(xs: List[A]): List[A] =
+    xs match
+      case head :: tail =>
+        head :: tail.flatMap(a => List(x, a))
+
+      case Nil =>
+        Nil

firepower-demo/src/main/scala/com/htmlism/firepower/demo/PrintPrograms.scala

@@ -13,9 +13,12 @@ object PrintPrograms extends ZIOAppDefault:
 
   private val programs =
     List[(String, String)](
-      "one-line.txt"  -> "one line",
-      "two-lines.txt" -> (Line.mkString _)
-        .apply(List("foo", "bar").map(Line(_)))
+      "one-line.txt"       -> "one line",
+      "two-lines.txt"      -> (Line.mkString _)
+        .apply(List("foo", "bar")),
+      "two-paragraphs.txt" -> (Line.mkString _)
+        .compose(Paragraph.mkLines)
+        .apply(List(Paragraph("foo", "bar"), Paragraph("alpha", "bravo")))
     )
 
   def run: Task[Unit] =