From 04a491c5511cb004702e1b02c93931e439413fb4 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bruce@bruce-hill.com>
Date: Mon, 24 Mar 2025 22:29:28 -0400
Subject: [PATCH] More lessons

---
 koans.tm                               |  3 +++
 lesson-templates/lesson-14-langs.tm    | 31 ++++++++++++++++++++++++++
 lesson-templates/lesson-15-min-max.tm  | 22 ++++++++++++++++++
 lesson-templates/lesson-16-reducers.tm | 31 ++++++++++++++++++++++++++
 4 files changed, 87 insertions(+)
 create mode 100644 lesson-templates/lesson-14-langs.tm
 create mode 100644 lesson-templates/lesson-15-min-max.tm
 create mode 100644 lesson-templates/lesson-16-reducers.tm

diff --git a/koans.tm b/koans.tm
index 8b5516f..556e6f3 100644
--- a/koans.tm
+++ b/koans.tm
@@ -22,6 +22,9 @@ LESSONS := [
     Lesson((./lessons/lesson-11-enums.tm), "Enums"),
     Lesson((./lessons/lesson-12-allocating.tm), "Allocating Memory"),
     Lesson((./lessons/lesson-13-paths.tm), "File Paths"),
+    Lesson((./lessons/lesson-14-langs.tm), "Embedded Languages"),
+    Lesson((./lessons/lesson-15-min-max.tm), "Min and Max"),
+    Lesson((./lessons/lesson-16-reducers.tm), "Reducers"),
 ]
 
 enum TestResult(Success(output:Text), Error(err:Text), WrongOutput(actual:Text, expected:Text)):
diff --git a/lesson-templates/lesson-14-langs.tm b/lesson-templates/lesson-14-langs.tm
new file mode 100644
index 0000000..6bb1911
--- /dev/null
+++ b/lesson-templates/lesson-14-langs.tm
@@ -0,0 +1,31 @@
+# Langs (Safe Embedded Languages)
+
+# `lang` defines custom text types with automatic escaping.
+lang HTML:
+
+    # Custom escaping rules can be created with `convert`
+    convert(t:Text -> HTML):
+        t = t:replace_all({$/&/="&amp;", $/</="&lt;", $/>/="&gt;"})
+        return HTML.from_text(t)
+
+    func paragraph(content:HTML -> HTML):
+        return $HTML"<p>$content</p>"
+
+
+# Type safety prevents injection:
+func greet(name:HTML -> HTML):
+    return $HTML"Hello, $name!"
+
+func main():
+
+    malicious_input := "<b>hello</b>"
+
+    safe := $HTML"User said: $malicious_input"
+
+    >> safe
+    = ???
+
+    >> safe:paragraph()
+    = ???
+
+    greeting := greet(malicious_input)  # This should fail
diff --git a/lesson-templates/lesson-15-min-max.tm b/lesson-templates/lesson-15-min-max.tm
new file mode 100644
index 0000000..5273fa7
--- /dev/null
+++ b/lesson-templates/lesson-15-min-max.tm
@@ -0,0 +1,22 @@
+# Min and Max
+
+struct Point(x:Int, y:Int)
+
+func main():
+
+    # `_min_` and `_max_` return the smaller or larger of two values:
+    >> 7 _min_ 3
+    = ???
+    >> "apple" _max_ "banana"
+    = "???"
+
+    # You can use an indexed key for choosing a maximum:
+    >> Point(1, 2) _max_.y Point(999, 0)
+    = Point(x=???, y=???)
+
+    >> [1, 2, 3] _min_.length [99, 100]
+    = [???]
+
+    # You can also use a method for choosing a maximum:
+    >> 5 _max_:abs() -999
+    = ???
diff --git a/lesson-templates/lesson-16-reducers.tm b/lesson-templates/lesson-16-reducers.tm
new file mode 100644
index 0000000..7324882
--- /dev/null
+++ b/lesson-templates/lesson-16-reducers.tm
@@ -0,0 +1,31 @@
+# Reductions
+
+func main():
+
+    # Reductions fold collections into a single value:
+    >> (+: [1, 2, 3])!
+    = ???
+    >> (*: [2, 3, 4])!
+    = ???
+
+    # If an empty argument is given, a `none` value is returned
+    empty := [:Int]
+    >> (+: empty)
+    = none
+
+    # Use `or` to provide a fallback:
+    >> (+: empty) or 100
+    = ???
+
+    # `_min_` and `_max_` work as reducers:
+    >> (_max_: [10, 30, 20])!
+    = ???
+    >> (_min_.length: ["x", "abcd", "yz"])!
+    = "???"
+
+    # Comprehensions inside reductions:
+    >> (+: i * 2 for i in [1, 2, 3])!
+    = ???
+
+    >> (+: i for i in 10 if i:is_prime())!
+    = 0