From 70917e529550d8b507dcd1c1ac65e600e1a48337 Mon Sep 17 00:00:00 2001
From: Nat Quayle Nelson <natquaylenelson@gmail.com>
Date: Thu, 19 Nov 2020 13:00:42 -0700
Subject: [PATCH] (let...)

---
 src/kiss/SpecialForms.hx          | 36 ++++++++++++++++++++++++++++++-
 src/test/cases/BasicTestCase.hx   |  4 ++++
 src/test/cases/BasicTestCase.kiss | 10 ++++++++-
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/kiss/SpecialForms.hx b/src/kiss/SpecialForms.hx
index 866b6c36..6b764608 100644
--- a/src/kiss/SpecialForms.hx
+++ b/src/kiss/SpecialForms.hx
@@ -6,6 +6,7 @@ import kiss.Reader;
 import kiss.Types;
 
 using kiss.Helpers;
+using kiss.Prelude;
 
 // Special forms convert Kiss reader expressions into Haxe macro expressions
 typedef SpecialFormFunction = (args:Array<ReaderExp>, convert:ExprConversion) -> Expr;
@@ -34,7 +35,40 @@ class SpecialForms {
 
         // TODO special form for local var declaration
 
-        // TODO let
+        map["let"] = (args:Array<ReaderExp>, convert:ExprConversion) -> {
+            var bindingList = switch (args[0]) {
+                case ListExp(bindingExps) if (bindingExps.length > 0 && bindingExps.length % 2 == 0):
+                    bindingExps;
+                default:
+                    throw '${args[0]} should be a list expression with an even number of sub expressions';
+            };
+            var bindingPairs = bindingList.groups(2);
+            var varDefs = [
+                for (bindingPair in bindingPairs)
+                    {
+                        name: switch (bindingPair[0]) {
+                            case Symbol(name) | TypedExp(_, Symbol(name)):
+                                name;
+                            default:
+                                throw 'first element of binding pair $bindingPair should be a symbol or typed symbol';
+                        },
+                        type: switch (bindingPair[0]) {
+                            case TypedExp(type, _):
+                                Helpers.parseTypePath(type);
+                            default: null;
+                        },
+                        isFinal: true, // Let's give (let...) variable immutability a try
+                        expr: convert(bindingPair[1])
+                    }
+            ];
+
+            var body = args.slice(1);
+            if (body.length == 0) {
+                throw '(let....) expression with bindings $bindingPairs needs a body';
+            }
+
+            EBlock([EVars(varDefs).withPos(), EBlock(body.map(convert)).withPos()]).withPos();
+        };
 
         // TODO special form for lambda
 
diff --git a/src/test/cases/BasicTestCase.hx b/src/test/cases/BasicTestCase.hx
index 323c2434..8b73882b 100644
--- a/src/test/cases/BasicTestCase.hx
+++ b/src/test/cases/BasicTestCase.hx
@@ -146,4 +146,8 @@ class BasicTestCase extends Test {
         Assert.equals([[1, 2], [3, 4]].toString(), BasicTestCase.myGroups1().toString());
         Assert.equals([[1, 2, 3], [4]].toString(), BasicTestCase.myGroups2().toString());
     }
+
+    function testLet() {
+        _testLet();
+    }
 }
diff --git a/src/test/cases/BasicTestCase.kiss b/src/test/cases/BasicTestCase.kiss
index b23bc54f..a3aff4f5 100644
--- a/src/test/cases/BasicTestCase.kiss
+++ b/src/test/cases/BasicTestCase.kiss
@@ -91,4 +91,12 @@
     (Prelude.groups [1 2 3 4] 2))
 
 (defun myGroups2 []
-    (Prelude.groups [1 2 3 4] 3 true))
\ No newline at end of file
+    (Prelude.groups [1 2 3 4] 3 true))
+
+(defun _testLet []
+    (let [a 5
+            b 6
+            :String c "stuff"]
+        (Assert.equals 5 a)
+        (Assert.equals 6 b)
+        (Assert.equals "stuff" c)))
\ No newline at end of file