From 7e3e4eb8b4b8711635aa6e05d90877bfdfcb4b6d Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Wed, 3 Aug 2022 20:25:46 -0700
Subject: Start the scheme base library.

---
 lib/scheme/base/20-let.csc | 76 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 lib/scheme/base/20-let.csc

(limited to 'lib/scheme/base/20-let.csc')

diff --git a/lib/scheme/base/20-let.csc b/lib/scheme/base/20-let.csc
new file mode 100644
index 0000000..96f0247
--- /dev/null
+++ b/lib/scheme/base/20-let.csc
@@ -0,0 +1,76 @@
+(export
+  lambda
+  let
+  let*
+  letrec
+  letrec*)
+(import (only (csc builtins)
+          define-syntax
+          lambda))
+(begin
+
+
+  (define-syntax letrec*
+    (syntax-rules ()
+      ((letrec* ((var1 init1) ...) body1 body2 ...)
+        (lambda ()
+          (define var1 init1)
+          ...
+          body1 body2 ...))))
+
+
+  (define-syntax letrec-generate-temp-names
+    (syntax-rules ()
+      ((letrec-generate-temp-names
+         ()
+         (temp1 ...)
+         ((var1 init1) ...)
+         body ...)
+        (letrec* ((temp1 init1)
+                  ...
+                  (var1 temp1)
+                  ...)
+          body ...))
+      ((letrec-generate-temp-names
+         (x y ...)
+         (temp ...)
+         ((var1 init1) ...)
+         body ...)
+        (letrec-generate-temp-names
+          (y ...)
+          (newtemp temp ...)
+          ((var1 init1) ...)
+          body ...))))
+
+
+  (define-syntax letrec
+    (syntax-rules ()
+      ((letrec ((var1 init1) ...) body1 body2 ...)
+        (letrec-generate-temp-names
+          (var1 ...)
+          ()
+          ((var1 init1) ...)
+          body1 body2 ...))))
+
+
+  (define-syntax let
+    (syntax-rules ()
+      ((let ((name val) ...) body1 body2 ...)
+        ((lambda (name ...) body1 body2 ...)
+         val ...))
+      ((let tag ((name val) ...) body1 body2 ...)
+        ((letrec ((tag (lambda (name ...)
+                         body1 body2 ...)))
+           tag)
+         val ...))))
+
+
+  (define-syntax let*
+    (syntax-rules ()
+      ((let* () body1 body2 ...)
+        (let () body1 body2 ...))
+      ((let* ((name1 val1) (name2 val2) ...)
+         body1 body2 ...)
+        (let ((name1 val1))
+          (let* ((name2 val2) ...)
+            body1 body2 ...))))))
-- 
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