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functions

summary

    This subchapter looks at functions.

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stub section

    This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.

    Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.

functions

    This subchapter looks at functions.

    Functions are named by a valid identifier.

    Quick summary of the rules for building valid function identifiers in several major languages, using regular expressions:

Ada	[a-zA-Z](_?[a-zA-Z0-9])*
ALGOL-68	[a-z][a-z0-9 ]*
Awk	[_a-zA-Z][_a-zA-Z0-9]*
B	[_a-zA-Z][_a-zA-Z0-9]*
BourneShell	[_a-zA-Z0-9]+
C	[_a-zA-Z][_a-zA-Z0-9]*
C#	[_a-zA-Z][_a-zA-Z0-9]*
C++	[_a-zA-Z][_a-zA-Z0-9]*
COBOL	[a-zA-Z][a-zA-Z0-9-]* 30 character maximum
Classic REXX	[a-zA-Z!?@#][a-zA-Z0-9!?@#]*
Common Lisp	anything without a space and is not a number
E	[_a-zA-Z][_a-zA-Z0-9]*
Eiffel	[a-zA-Z][_a-zA-Z0-9]*
F#	[_a-zA-Z][_a-zA-Z0-9']*
FORTRAN	[A-Z][A-Z0-9]* maximum of six characters
Forth	anything without a space and is not a number
GNU-bc	[a-z][a-z0-9_]*
Haskell	[_a-z][_a-zA-Z0-9']*
Java	[_a-zA-Z$][_a-zA-Z0-9$]*
JavaScript	[_a-zA-Z$][_a-zA-Z0-9$]*
Lisp	anything without a space and is not a number
Maple	[_a-zA-Z][_a-zA-Z0-9]*
Mathematica	[a-zA-Z][a-zA-Z0-9]*
Matlab	[a-zA-Z][_a-zA-Z0-9]*
Mercury	[_a-z][_a-zA-Z0-9]*
merd	[_a-z][_a-zA-Z0-9]*[!?']*
Modula-3	[a-zA-Z][_a-zA-Z0-9]*
MUMPS	[a-zA-Z%][a-zA-Z0-9]*
OCaml	[_a-z][_a-zA-Z0-9']*
Pascal	[a-zA-Z][a-zA-Z0-9]*
Perl	[_a-zA-Z0-9]+
Perl6	[_a-zA-Z0-9]+
PHP	[_a-zA-Z][_a-zA-Z0-9]*
PL/I	[a-zA-Z][a-zA-Z0-9]*
Pliant	[_a-zA-Z][_a-zA-Z0-9]* or '[^']*'
Prolog	[_a-z][_a-zA-Z0-9]*
Python	[_a-zA-Z][_a-zA-Z0-9]*
Rebol	[_a-zA-Z?!.'+*&|=~-][_a-zA-Z0-9?!.'+*&|=~-]* or [^0-9[](){}":;/][^ \n\t[](){}":;/]*
Ruby	[_a-zA-Z][_a-zA-Z0-9]*[!?]?
Scheme	[_a-zA-Z!0&*/:<=>?^][_a-zA-Z!0&*/:<=>?^0-9.+-]*
SmallTalk	[a-zA-Z][a-zA-Z0-9]*
SML	[_a-z][_a-zA-Z0-9']*
Tcl	[^ \t\n\r\f]+

   “Procedure names should reflect what they do; function names should reflect what they return.ÊFunctions are used in expressions, often in things like ifs, so they need to read appropriately.
        if(checksize(x))
   “is unhelpful because we can’t deduce whether checksize returns true on error or non-error; instead
        if(validsize(x))
   “makes the point clear and makes a future mistake in using the routine less likely.” —Rob Pike, Notes on Programming in C, February 21, 1989

    Suggestion from Bjarne Stroustrup, creator of C++
        [g] Don’t use inline functions; except as a significant optimization.

mismatched types

    According to Brian Kernighan, co-creator of the AWK and AMPL programming languages and co-author of K&R C, one of the three most common errors for new programmers is mismatched types in a fucntion call.

Ada

other

   “2. Functions delay binding: data structures induce binding. Moral: Structure data late in the programming process.” —Alan Perlis, Epigrams on Programming, ACM’s SIGPLAN Notices Volume 17, No. 9, September 1982, pages 7-13

   “9. It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.” —Alan Perlis, Epigrams on Programming, ACM’s SIGPLAN Notices Volume 17, No. 9, September 1982, pages 7-13

   “94. Interfaces keep things tidy, but don’t accelerate growth: Functions do.” —Alan Perlis, Epigrams on Programming, ACM’s SIGPLAN Notices Volume 17, No. 9, September 1982, pages 7-13

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