From 6a297bfcace1151d0f1840c8d7408c128c740962 Mon Sep 17 00:00:00 2001
From: Nat Quayle Nelson <natquaylenelson@gmail.com>
Date: Sat, 16 Jan 2021 21:27:43 -0700
Subject: [PATCH] ifLet

---
 kiss/src/kiss/Macros.hx                | 48 +++++++++++++++++++++++++-
 kiss/src/test/cases/BasicTestCase.hx   |  4 +++
 kiss/src/test/cases/BasicTestCase.kiss | 18 +++++++++-
 3 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/kiss/src/kiss/Macros.hx b/kiss/src/kiss/Macros.hx
index cc0ecaea..917c750a 100644
--- a/kiss/src/kiss/Macros.hx
+++ b/kiss/src/kiss/Macros.hx
@@ -419,7 +419,53 @@ class Macros {
             return null;
         };
 
-        // TODO macros for ifLet, whenLet (for assign then truthy check), caseLet (for extracting from enums)
+        // Macros that null-check and extract patterns from enums (inspired by Rust)
+        function ifLet(wholeExp:ReaderExp, exps:Array<ReaderExp>, k:KissState) {
+            wholeExp.checkNumArgs(2, null, "(ifLet [[enum bindings...]] [thenExp] [?elseExp])");
+            var b = wholeExp.expBuilder();
+
+            var thenExp = exps[1];
+            var elseExp = if (exps.length > 2) {
+                exps[2];
+            } else {
+                b.symbol("null");
+            };
+
+            var bindingList = exps[0].bindingList("ifLet");
+            var firstPattern = bindingList.shift();
+            var firstValue = bindingList.shift();
+
+            return b.call(
+                b.symbol("if"), [
+                    firstValue,
+                    b.call(
+                        b.symbol("case"), [
+                            firstValue,
+                            b.call(
+                                firstPattern, [
+                                    if (bindingList.length == 0) {
+                                        exps[1];
+                                    } else {
+                                        ifLet(wholeExp, [
+                                            b.list(bindingList)
+                                        ].concat(exps.slice(1)), k);
+                                    }
+                                ]),
+                            b.call(
+                                b.symbol("otherwise"), [
+                                    elseExp
+                                ])
+                        ]),
+                    elseExp
+                ]);
+        }
+
+        macros["ifLet"] = ifLet;
+
+        // TODO whenLet
+        // wholeExp.checkNumArgs(2, null, "(whenLet [[enum bindings...]] [body...])");
+        // TODO unlessLet
+        // wholeExp.checkNumArgs(2, null, "(unlessLet [[enum bindings...]] [body...])");
 
         // TODO use expBuilder()
         function awaitLet(wholeExp:ReaderExp, exps:Array<ReaderExp>, k:KissState) {
diff --git a/kiss/src/test/cases/BasicTestCase.hx b/kiss/src/test/cases/BasicTestCase.hx
index df82a90e..501ce124 100644
--- a/kiss/src/test/cases/BasicTestCase.hx
+++ b/kiss/src/test/cases/BasicTestCase.hx
@@ -269,6 +269,10 @@ class BasicTestCase extends Test {
     function testAssignArith() {
         _testAssignArith();
     }
+
+    function testPatternLets() {
+        _testPatternLets();
+    }
 }
 
 class BasicObject {
diff --git a/kiss/src/test/cases/BasicTestCase.kiss b/kiss/src/test/cases/BasicTestCase.kiss
index d77fe717..34e59939 100644
--- a/kiss/src/test/cases/BasicTestCase.kiss
+++ b/kiss/src/test/cases/BasicTestCase.kiss
@@ -436,4 +436,20 @@
     (/= num 25 2)
     (Assert.equals 1 num)
     (-= num 5 6)
-    (Assert.equals -10 num))
\ No newline at end of file
+    (Assert.equals -10 num))
+
+(defun _testPatternLets []
+    (let [some5 (Some 5)
+            some6 (Some 6)
+            none None
+            :Null<Option<Any>> oops null]
+        (ifLet [(Some a) some5
+                (Some b) some6]
+                (Assert.equals 11 (+ a b))
+            (Assert.fail))
+        (ifLet [(Some a) oops]
+            (Assert.fail))
+        (ifLet [(Some (or 5 6)) some5]
+            (Assert.pass))
+        (ifLet [(Some a) none]
+            (Assert.fail))))
\ No newline at end of file