pred

#pred

##Syntax pred ( expn )

##Description The pred function accepts an integer, character, or an enumerated value and returns the integer minus one, the previous character, or the previous value in the enumeration. For example, pred ( 7 ) is 6.

##Example This part of a Turing program fills up array a with the enumerated values red, yellow, green, red, yellow, green, etc.

    type colors : enum ( green, yellow, red )
    var a : array 1 .. 100 of colors
    var c : colors := colors . red
    for i : 1 .. 100
        a ( i ) := c
        if c = colors . green then
            c := colors . red
        else
            c := pred ( c )
        end if
    end for

##Details It is illegal to apply pred to the first value of an enumeration.

##See also succ.html, lower.html and upper.html functions.