[racket] λ vs lambda

[Michael Rice]

The code below (kons) gets flagged in R5RS:  

define: not allowed in an expression context in: (define dispatch (λ (m) (cond ((= m 0) x) ((= m 1) y) (else (error "Argument not 0 or 1 -- KONS" m)))))

Works fine if I replace the lambda symbols with "lambda".

Cause?

Michael

============= 

From page 91 in SICP (slightly modified):

(define kons (λ (x y)

    (define dispatch (λ (m)

        (cond ((= m 0) x)

              ((= m 1) y)

              (else (error "Argument not 0 or 1 -- KONS" m)))))

    dispatch))

(define (kar z)

    (z 0))

(define (kdr z)

    (z 1))

[Ray Racine]

R5RS does not specify 'λ'.  It's just another character like 'A' or 'a'.  In Racket, the language, λ and lambda are equivalent.

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[Grant Rettke]

Can we hack DrRacket to display a lambda instead of the word lambda like pretty-mode in emacs?

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[Danny Yoo]

On Mon, May 14, 2012 at 11:09 AM, Michael Rice <limi...@gmail.com> wrote:

> The code below (kons) gets flagged in R5RS:

Unfortunately, the error message is not reporting the leftmost error
in this situation. The real source of the problem is that the lambda
character λ is not in R5RS. The whole purpose of the r5rs language is
to be extremely conservative.

[Jens Axel Søgaard]

2012/5/14 Michael Rice <limi...@gmail.com>:

> The code below (kons) gets flagged in R5RS:
>
> define: not allowed in an expression context in: (define dispatch (λ (m)
> (cond ((= m 0) x) ((= m 1) y) (else (error "Argument not 0 or 1 -- KONS"
> m)))))
>
> Works fine if I replace the lambda symbols with "lambda".
>
> Cause?

Insert this macro definition at the top of your R5RS code.

(define-syntax λ
(syntax-rules ()
((_ . more) (lambda . more))))

--
Jens Axel Søgaard