calc/help/unexpected

Unexpected

    While calc is C-like, users of C will find some unexpected
    surprises in calc syntax and usage.  Persons familiar with C should
    review this file.


    The Comma
    =========

    The comma is also used for continuation of obj and mat creation
    expressions and for separation of expressions to be used for
    arguments or values in function calls or initialization lists.  The
    precedence order of these different uses is:  continuation,
    separator, comma operator.  For example, assuming the variables a,
    b, c, d, e, and object type xx have been defined, the arguments
    passed to f in:

	    f(a, b, c, obj xx d, e)

    are a, b, c, and e, with e having the value of a newly created xx
    object.  In:

	    f((a, b), c, (obj xx d), e)

    the arguments of f are b, c, d, e, with only d being a newly
    created xx object.

    In combination with other operators, the continuation use of the
    comma has the same precedence as [] and ., the separator use the
    same as the comma operator.  For example, assuming xx.mul() has
    been defined:

	    f(a = b, obj xx c, d = {1,2} * obj xx e = {3,4})

    passes two arguments: a (with value b) and the product d * e of two
    initialized xx objects.


    ^ is not xor
    ============

    In C, ^ is the xor operator.  Like the '**', '^' is the
    exponentiation operator.  The expression:

	    a^b

    yields "a to the b power", NOT "a xor b".

    Note that 'b' must be an integer.  Also if 'a' == 0, 'b'
    must be >= 0 as well.

    To raise to a non-integer power, use the power() builtin function.


    ** is exponentiation
    ====================

    As was suggested in the '^ is not xor' section, the expression:

	    a**b

    yields "a to the b power", NOT "a xor b".

    Note that 'b' must be an integer.  Also if 'a' == 0, 'b'
    must be >= 0 as well.

    To raise to a non-integer power, use the power() builtin function.


    op= operators associate left to right
    =====================================

    Operator-with-assignments:

	    +=  -=  *=  /=  %=  //=  &=  |=  <<=  >>=  ^=  **=

    associate from left to right instead of right to left as in C.
    For example:

	    a += b *= c

    has the effect of:

	    a = (a + b) * c

    where only 'a' is required to be an lvalue.  For the effect of:

	    b *= c; a += b

    when both 'a' and 'b' are lvalues, use:

	    a += (b *= c)


    || yields values other than 0 or 1
    ==================================

    In C:

	    a || b

    will produce 0 or 1 depending on the logical evaluation
    of the expression.  In calc, this expression will produce
    either 'a' or 'b' and is equivalent to the expression:

	    a ? a : b

    In other words, if 'a' is true, then 'a' is returned, otherwise
    'b' is returned.


    && yields values other than 0 or 1
    ==================================

    In C:

	    a && b

    will produce 0 or 1 depending on the logical evaluation
    of the expression.  In calc, this expression will produce
    either 'a' or 'b' and is equivalent to the expression:

	    a ? b : a

    In other words, if 'a' is true, then 'b' is returned, otherwise
    'a' is returned.


    / is fractional divide, // is integral divide
    =============================================

    In C:

	    x/y

    performs integer division when 'x' and 'y' are integer types.
    In calc, this expression yields a rational number.

    Calc uses:

	    x//y

    to perform division with integer truncation and is the equivalent to:

	    int(x/y)


    | and & have higher precedence than ==, +, -, *, / and %
    ========================================================

    Is C:

	    a == b | c * d

    is interpreted as:

	    (a == b) | (c * d)

    and calc it is interpreted as:

	    a == ((b | c) * d)


    calc always evaluates terms from left to right
    ==============================================

    Calc has a definite order for evaluation of terms (addends in a
    sum, factors in a product, arguments for a function or a matrix,
    etc.).  This order is always from left to right. but skipping of
    terms may occur for ||, && and ? : .

    Consider, for example:

	    A * B + C * D

    In calc above expression is evaluated in the following order:

	    A
	    B
	    A * B
	    C
	    D
	    C * D
	    A * B + C * D

    This order of evaluation is significant if evaluation of a
    term changes a variable on which a later term depends.  For example:

	    x++ * x++ + x++ * x++

    in calc returns the value:

	    x * (x + 1) + (x + 2) * (x + 3)

    and increments x as if by x += 4.  Similarly, for functions f, g,
    the expression:

	    f(x++, x++) + g(x++)

    evaluates to:

	    f(x, x + 1) + g(x + 2)

    and increments x three times.


    &A[0] and A are different things in calc
    ========================================

    In calc, value of &A[0] is the address of the first element, whereas
    A is the entire array.


    *X may be used to to return the value of X
    ==========================================

    If the current value of a variable X is an octet, number or string,
    *X may be used to to return the value of X; in effect X is an
    address and *X is the value at X.


    freeing a variable has the effect of assigning the null value to it
    ===================================================================

    The freeglobals(), freestatics(), freeredc() and free() free
    builtins to not "undefine" the variables, but have the effect of
    assigning the null value to them, and so frees the memory used for
    elements of a list, matrix or object.

    Along the same lines:

	    undefine *

    undefines all current user-defined functions.  After executing
    all the above freeing functions (and if necessary free(.) to free
    the current "old value"), the only remaining numbers as displayed by

	    show numbers

    should be those associated with epsilon(), and if it has been
    called, qpi().