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:

(import (rename (only (rnrs base) lambda) (lambda λ)))

R7RS:

(import (rename (only (scheme base) lambda) (lambda λ)))

Using a macro

(define-syntax λ (syntax-rules () ((λ . rest) (lambda . rest))))

or the non-standard:

(define-macro (λ . rest) `(lambda ,@rest))

Spelling out `lambda` in source files but displaying `λ` on screen

See 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;|.