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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.lisp
Subject: Re: X in every language syndrome
Date: Sun, 7 Jul 2024 05:58:57 -0000 (UTC)
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On 2024-07-06, B. Pym <No_spamming@noWhere_7073.org> wrote:
> [ Another poster: ]
>
>> TXR Lisp.
>> 
>> Having defined:
>> 
>>   (defun bellied-p (num)
>>     (let ((d (digits num)))
>>       (and (= 4 (len d))
>> 	   (< (+ [d 0] [d 3])
>> 	      (+ [d 1] [d 2])))))
>> 
>> We casually do this at the prompt:
>> 
>>   1> [find-max [partition-by bellied-p (range 1000 9999)] :
>> 	       [iff [chain car bellied-p] len (ret 0)]]
>>   (1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932
>>    1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945
>>    1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958
>>    1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971
>>    1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984
>>    1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
>>    1998 1999)
>
> Shorter.
>
> Gauche Scheme:
>
> (use gauche.sequence) ;; group-contiguous-sequence find-max
> ,print-mode pretty #t length #f width 64
>
> (define (bellied? n)
>   (define (d i) (mod (div n (expt 10 i)) 10))
>   (> (+ (d 1) (d 2))
>      (+ (d 0) (d 3))))
>
> (find-max
>   (group-contiguous-sequence (filter bellied? (iota 9000 1000)))
>  :key length)
>
>  ===>
> (1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931
>  1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943
>  1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955
>  1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
>  1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979
>  1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991
>  1992 1993 1994 1995 1996 1997 1998 1999)

(defun bellied (num)
  (match (@a @b @c @d) (digits num)
    (< (+ a d) (+ b c)))) 

[find-max (split* (range 1000 9999) (op where [notf bellied])) : len]

OR:

(defun not-bellied (num)
  (match (@a @b @c @d) (digits num)
    (>= (+ a d) (+ b c)))) 

[find-max (split* (range 1000 9990) (op where not-bellied)) : len]

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca