Programming Terminology – Origin of ‘Calling’ a Function

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I've always wondered why one calls a function as opposed to, for example, executing it.

A Google search for function call etymology and similar terms turns up nothing useful, Wikipedia doesn't mention it, online dictionaries have either no entry at all or no etymology section.

Where did the notion of 'calling' a function come from?

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The word call goes back at least to Fortran, the first widely used programming language. In Fortran, CALL is a keyword that passes control to a subroutine. It's not clear why John Backus chose that word to invoke subroutines -- you may need to read one or more biographies of Backus to discover that -- but it seems likely that the use in Fortran is the reason that we use the word call today with respect to functions, methods, etc.

Note that the use of call with respect to functions and other subroutines also fits well with several English-language definitions of call:

to make a brief visit
to demand something
to rouse from sleep
to invite

Related Solutions

Origin of the Term ‘Red/Black Tree’

EDIT: Answer from Professor Guibas:

from Leonidas Guibas guibas@cs.stanford.edu to of the "Red-Black" term mailed-by cs.stanford.edu hide details 16:16 (0 minutes ago)

we had red and black pens for drawing the trees.

I believe the term first appeared in "A dichromatic framework for balanced trees" from Leonidas J. Guibas and Robert Sedgewick in 1978.

Where did the notion of “one return only” come from

"Single Entry, Single Exit" was written when most programming was done in assembly language, FORTRAN, or COBOL. It has been widely misinterpreted, because modern languages do not support the practices Dijkstra was warning against.

"Single Entry" meant "do not create alternate entry points for functions". In assembly language, of course, it is possible to enter a function at any instruction. FORTRAN supported multiple entries to functions with the ENTRY statement:

      SUBROUTINE S(X, Y)
      R = SQRT(X*X + Y*Y)
C ALTERNATE ENTRY USED WHEN R IS ALREADY KNOWN
      ENTRY S2(R)
      ...
      RETURN
      END

C USAGE
      CALL S(3,4)
C ALTERNATE USAGE
      CALL S2(5)

"Single Exit" meant that a function should only return to one place: the statement immediately following the call. It did not mean that a function should only return from one place. When Structured Programming was written, it was common practice for a function to indicate an error by returning to an alternate location. FORTRAN supported this via "alternate return":

C SUBROUTINE WITH ALTERNATE RETURN.  THE '*' IS A PLACE HOLDER FOR THE ERROR RETURN
      SUBROUTINE QSOLVE(A, B, C, X1, X2, *)
      DISCR = B*B - 4*A*C
C NO SOLUTIONS, RETURN TO ERROR HANDLING LOCATION
      IF DISCR .LT. 0 RETURN 1
      SD = SQRT(DISCR)
      DENOM = 2*A
      X1 = (-B + SD) / DENOM
      X2 = (-B - SD) / DENOM
      RETURN
      END

C USE OF ALTERNATE RETURN
      CALL QSOLVE(1, 0, 1, X1, X2, *99)
C SOLUTION FOUND
      ...
C QSOLVE RETURNS HERE IF NO SOLUTIONS
99    PRINT 'NO SOLUTIONS'

Both these techniques were highly error prone. Use of alternate entries often left some variable uninitialized. Use of alternate returns had all the problems of a GOTO statement, with the additional complication that the branch condition was not adjacent to the branch, but somewhere in the subroutine.

Thanks to Alexey Romanov for finding the original paper. See http://www.cs.utexas.edu/users/EWD/ewd02xx/EWD249.PDF, page 28 (printed page number is 24). Not limited to functions.

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Related Solutions

Origin of the Term ‘Red/Black Tree’

Where did the notion of “one return only” come from

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