Go To Statement Considered Harmful

1
Go To Statement Considered Harmful

• by E.W. Dijkstra Mar. 1968
• presented by Yuanhua Qu
• for spring 2003 CS5391

2
Go To Statement Considered Harmful

• Overview
• Two Remarks
• Process
• The Go To Statement
• Acknowledgment

3
Overview

• The quality of programmers is a decreasing
  function of the density of go to statements in
  the programs they produce.
• The go to statement should be abolished from all
  "higher level" programming languages (i.e.
  everything except, perhaps, plain machine code).

4
Two Remarks

• First remark
• programmers activity ends when correct program
  is constructed.
• Process is the true subject matter of his
  activity
• accomplish the desired effect
• satisfy the desired specifications in its dynamic
  behavior

5
Two Remarks

• Second remark
• Our intellectual powers are rather geared to
  master static relations.
• Our powers to visualize processes evolving in
  time are relatively poorly developed.
• Therefore should shorten the gap between the
  static program and the dynamic process

6
Process (continued)

• textual index
• is a pointer to a suitable place in the text
• The progress of a process
• can always be uniquely characterized by a (mixed
  ) sequence of textual and/or dynamic indices.

7
Process (continued)

• Indices provide independent coordinates in which
  to describe the progress of the process.
• An independent coordinate system can describe the
  process in a helpful and manageable way.

8
The Go To Statement

• Unbridled use of the go to statement has an
  immediate consequence that it becomes terribly
  hard to find a meaningful set of coordinates in
  which to describe the process progress.
• The go to statement as it stands is just too
  primitive it is too much an invitation to make a
  mess of ones program.

9
Acknowledgment

• The remark about the undesirability of the go to
  statement is far from new. Trace back to
  C.A.R.Hoare and Wirth.
• Guiseppe Jacopini seems to have proved the
  (logical) superfluousness of the go to statement.
  
• The end.