FNname(expression, ...)

Calls a function defined with DEF FNname(...). The call appears inside an expression (for example on the right-hand side of =, or as part of PRINT).

There is no space between FN and the function name (e.g. FNadd(1,2), not FN add(1,2)).
The number of arguments and their types must match the definition.
The return type is determined by the function name suffix:
- no suffix - integer
- name ending with # - real
- name ending with $ - string
A function defined with DEF FN... returns its value on a line that begins with = in the definition.

Integer result

DEF FNadd(A, B)
= A + B
 
X = FNadd(2, 3)
PRINT X

Real result

DEF FNmean#(A#, B#)
= (A# + B#) / 2#
 
M# = FNmean#(1.5#, 2.5#)
PRINT M#

String result

DEF FNgreet$(NAME$)
= "HELLO, " + NAME$
 
PRINT FNgreet$("WORLD")

Calling an undefined function, supplying the wrong number of arguments, or passing mismatched types raises a runtime error (catchable with ON ERROR PROCname).
If the definition does not end with a leading = return line, calling the function is invalid.

See also:
DEF PROC ENDPROC Parameter types