INTRINSIC (BUILT-IN) FUNCTIONS

A FUNCTION, built-in or otherwise, can be used anywhere that
an expression can be used.  It can be a part of an expression,
and it can have an expression as it's argument.  It returns a
single value, which is defined by the descriptions below.
Some functions return string values, and some return numeric ones.

ABS(<numeric expression>)
Returns the absolute value of <numeric expression>.  In other words,
the expression is evaluated;  if the result is minus, the minus
sign is removed to make it positive.
Examples:  ABS(X-5*SIN(Y))    ABS(B^2-4*A*C)

ASC(<string expression>)
Returns the ASCII code of the first character of <string expression>.
(i.e. the number which corresponds with the ASCII character)
Examples:  ASC("A")    ASC(ANS$)    ASC(A$(N))

ATN(<numeric expression>)
Returns the arctangent of <numeric expression>, which is in radians.
Examples:  ATN(RADIANS)    ATN(DEGREES*PI/180)    ATN(.053)

* CALL(<numeric expression>,<numeric expression>)
Calls a machine language subroutine at the address indicated by
the first <numeric expression>, with the value of the second
<numeric expression> in registers D&E.  The CALL function
evaluates to the number which is returned in registers D&E.
The returned value in D&E is in the range -32768 to +32767.
Example:   PRINT CALL(PLOT,X)

CHR$(<numeric expression>)
Returns a single character string whose ASCII code is <numeric expression>.
Examples:  CHR$(7)    CHR$(48+NUM)    CHR$(CONTROL)

COS(<numeric expression>)
Returns the cosine of the angle <numeric expression>, which
is in radians.  Example:  COS(DEG*3.14159/180)

EOF(<numeric expression>)
Returns false (0) if an end-of-file has not been encountered,
or true (-1) if an end-of-file has been encountered, during
the last read operation from a file through the logical unit
specified by <numeric expression>.
Examples:    IF EOF(2) THEN GOTO QUIT    LET CASFLG=EOF(4)

EXP(<numeric expression>)
Returns the constant e (2.718282) to the <numeric expression> power.
Examples:  EXP(1)    EXP(0)    EXP(X+Y*2)

FILEXISTS(<string expression>)
Returns with 0 (false) if the file named by the string expression
does not exist.  Returns with -1 (true) if the file does exist.
Example:   IF FILEXISTS("STARTREK") THEN GOTO FOUND ELSE GOTO NOTFOUND

FRE(<expression>)
Returns the amount of free (unused) space in memory.  Because
the null string ("") takes less space in memory, this form will
return a slightly larger number than a numeric argument.
Examples:  FRE("")    FRE(0)    FRE(1)

* HEX(<hexadecimal string>)
Returns the decimal equivalent of the <hexadecimal string>.
Examples:   LET ADDR=HEX(HADDR$)    FOR N=0 TO HEX("A")















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