Add unicode-lambda recipe

recipes/unicode-lambda.md

@@ -0,0 +1,55 @@
+# Unicode lambda
+
+## Problem
+
+Instead of
+
+`(lambda (a b c) (* a (+ b c))`
+
+you'd like to type
+
+`(λ (a b c) (* a (+ b c)))`
+
+i.e. use the Unicode greek letter lambda in your Scheme code.
+
+## Solution
+
+### Using import renaming
+
+R6RS:
+
+```Scheme
+(import (rename (only (rnrs base) lambda) (lambda λ)))
+```
+
+R7RS:
+
+```Scheme
+(import (rename (only (scheme base) lambda) (lambda λ)))
+```
+
+### Using a macro
+
+```Scheme
+(define-syntax λ (syntax-rules () ((λ . rest) (lambda . rest))))
+```
+
+or the non-standard:
+
+```Scheme
+(define-macro (λ . rest) `(lambda ,@rest))
+```
+
+### Spelling out `lambda` in source files but displaying `λ` on screen
+
+See [Display Unicode symbols in Emacs](https://cookbook.scheme.org/display-unicode-symbols-in-emacs/).
+
+### Safely storing `λ` in text files
+
+`λ` is one Unicode codepoint, so changing the Unicode normalization
+form does not change the way `λ` characters are encoded. In R7RS `λ`
+can also be escaped using vertical bar syntax as `|\x3bb;|`.
+
+## See also
+
+[Unicode lambda at Scheme Surveys](https://doc.scheme.org/surveys/unicode-lambda/)

www-index.scm

@@ -48,7 +48,8 @@
  ("Macros"
   "bind-optional-arguments"
   "check-for-symbol-in-syntax-rules"
-  "define-symbols")
+  "define-symbols"
+  "unicode-lambda")
 
  ("Tool integrations"
   "display-unicode-symbols-in-emacs"))