Sample 19. Symbolic Functions

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19. Symbolic Functions
For any function, a corresponding symbolic function can be defined to display the expression rather than evaluate it. For example:

       minus=: [ , '-'"_ , ]
       'a' minus 'b'
    a-b

       list=: 'abcd'
       table=: 4 4$'ABCDEFGHIJKLMNOP'
       minus/list
    a-b-c-d

       (minus/\list);('01'minus"0/list);(minus//.table);table
    +-------+---+-------+----+
    |a      |0-a|A      |ABCD|
    |a-b    |0-b|B-E    |EFGH|
    |a-b-c  |0-c|C-F-I  |IJKL|
    |a-b-c-d|0-d|D-G-J-M|MNOP|
    |       |   |H-K-N  |    |
    |       |1-a|L-O    |    |
    |       |1-b|P      |    |
    |       |1-c|       |    |
    |       |1-d|       |    |
    +-------+---+-------+----+

       (,.list)=: 4 3 2 1
       (". minus/\list) ,: (-/\4 3 2 1)
    4 1 3 2
    4 1 3 2

       3 (minus/\ ; minus/\.) 'abcdefg'
    +-----+-------+
    |a-b-c|d-e-f-g|
    |b-c-d|a-e-f-g|
    |c-d-e|a-b-f-g|
    |d-e-f|a-b-c-g|
    |e-f-g|a-b-c-d|
    +-----+-------+

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