Meta-programming important for Psychology of Programming

[Massimo Dentico]

Excerpt  from  "Getting Rid of the Single Notation  Paradigm  with
Multiple Views" (emphasis mine):

- http://www.ppig.org/papers/11th-sajaniemi.html

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Introduction

[...]

The  normal  program text representation is all  that  a  compiler
needs  but humans need multiple representations, or views, of  the
same  program to support the construction of different aspects  of
mental representations.

[...]

The  method proposed in this paper is a step towards the direction
proposed  by Green. We give programmers an opportunity to  utilize
multiple  editable views of the same program. In other words,  the
system described in this paper is capable of representing programs
in  various  notations  supporting various types  of  information.
Moreover,  programs  can  be edited through  most  views  enabling
programmers not only to extract information in multiple  notations
but  also  to fully work in these notations. As a consequence,  it
becomes  almost  impossible to say which of the notations  is  the
'right' one, i.e., obeys the syntax of the programming language as
understood  by the compiler. Thus, ***the role of the  programming
language  changes  from a syntax definition  to  a  more  semantic
description.***
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A  leit-motiv in Tunes: syntaxes (notations) should be constructed
dynamically, when necessary, and they should not be fixed once for
all.

However,  from  the  point  of view of the  compiler  (thus  meta-
programming),  it  is  not  true that  "The  normal  program  text
representation is all that a compiler needs ...": different views,
or   intermediate  representations  (AST,  DAG,  RTL,  ...),   are
necessary even to the compiler in order to complete its task.



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Views in Action

We have implemented a program editor framework, VinEd (Sajaniemi &
Ikonen, 1998), that is capable of showing multiple editable  views
of  programs. An optimal set of views is, however, beyond  current
knowledge  of  program  representations and program  comprehension
process.  It  may even be impossible to define any  representation
that  every individual can call sensible, and views probably  need
to  be defined according to the environment and background of  the
programmer  (Shneiderman & al., 1986). This problem is  solved  in
VinEd  by  ***letting programmers define their own views  and  add
them  to  the system. As programmers are programming experts  they
are  able, and supposedly also keen, to create supporting programs
that construct views that they feel to be helpful for their tasks.
VinEd  is  shipped with some ready-made views for some programming
languages but users are supposed to add their own views.***

In  VinEd,  a  view  can  be any text obtained  by  applying  some
***transformer program*** to the original file. As the output of a
transformer   is   text  (and  not  a  graphical  representation),
programming  new  transformers is relatively easy.  If  a  reverse
transforming program is also given, files can be edited  (and  not
just  browsed) in the view. For example, the list of all  function
names  in  a  program facilitates comprehension of the program  by
showing   structured   information  and  the   underlying   design
(Shneiderman & al., 1986). ***A Pascal programmer can easily  make
a  short program (using a single line UNIX shell script consisting
of  a  call  of the grep command with the result piped  to  a  sed
command)  that  makes  such a list for his  or  her  own  programs
(though  the  solution  in  the  general  case  is  somewhat  more
tedious).*** Thus he or she can see the list in a view window with
the  program text in another window. Even the reverse transforming
is  simple  in this case and hence the programmer can  change  the
name  of a function in the function name list, and the system will
automatically  apply  the reverse filtering and  thus  change  all
occurrences  of  that  name  in the  program.  Views  are  updated
automatically  so  that  they  reflect  all  the   time    editing
operations made so far.

[...]
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It  is  obvious  that these transformer programs, which  construct
views  of  the program in examination, are meta-programs (programs
that  manipulate  and/or produce programs) and,  contrary  to  the
example described in the text, the meta-language could be the same
of the target language (providing the suitable infrastructure). As
a side note, Domain Specific Languages (DSLs) are a kind of "view"
(notation, syntax).

Moreover it is desirable that the development environment is  open
(open  implementation): many parts (if not all) of the programming
environment are available to the application programmer like,  for
example, in Smalltalk, Forth or Pliant.

This paper shows the importance of meta-programming even from  the
psychological-cognitive point of view.



The home page of Psychology of Programming Interest Group (PPIG):
- http://www.ppig.org/

-- 
Massimo Dentico