Re: What's the best language to learn? [was Re: Should I learn C or Pascal?]

[ok@goanna.cs.rmit.edu.au (Richard A. O'Keefe)]

Here's the reference I promised.

	The IMP Language and Compiler
	P. D. Stephens
	EMAS report 6
	Department of Computer Science, University of Edinburgh

My copy says "Reprinted 1977"; it was also apparently published in
The Computer Journal.

IMP is basically a sort of Algol with dynamic arrays, records, pointers,
bitwise operations, strings, and nested procedures.  (Pointers to
procedures were at one time provided, but dropped because they felt that
the scope rules -- similar to Ada 95's -- "emasculated" the feature.)
It's rather like C, but somewhat higher level.

Here's the quotation:

	The EMAS programmers who had previous experience of high-level
	languages adapted easily to system programming in IMP.  They
	produced compact, highly structured programs, which were easy
	to maintain or amend despite defects incommentary and/or
	documentation.  They seldom worried about the efficiency of
	object code produced by the compiler, but their programs
	generally performed well.  This group included the most productive
	programmers working on the [EMAS operating system] project.
	
	Programmers with a background of assembly language were less
	happy with IMP and seldom used its more advanced features such
	as recursion.  They produced well commented and documented
	programs that nevertheless proved difficult to maintain since they
	lacked structure.  This group worried about the efficiency of
	object code produced by the compiler to the extent of examining
	the listings of code produced, yet their programs were often
	large in size and slow in execution.  Some of the least productive
	programmers were included in this group.

Earlier in the report, they say that

	Two routines in EMAS and twnty in the compiler have been hand-coded
	[in assembler].  The gains in performance or reductions in size
	have varied from an encouraging 2% to a rather discouraging 40%.
	The majority have fallen into the 10% to 20% range.  One routine
	in EMAS -- the interrupt analysis routine -- was originally written
	in assembly code.  This routine has recently been rewritten in IMP
	and this time the IMP version is smaller by 11% and presumably
	faster by a like amount.
...
	The effect of [improvements to the code generator, most importantly
	the register allocator] is that the Release 8 compiler produces
	about half the amount of object code that Release 1 produced for
	the same program.  Release 8 object code is rather more than twice
	as fast as Release 1 object code.  Since the compiler is written
	in IMP, compiling speeds have increased similarly.  These figures
	enable the 4 months spent hand coding analysis routines to be seen
	as the waste of effort it undoubtedly was.

The bottom line is that thinking in assembly language terms, whether the
programmers actually _wrote_ in assembly language or an Algol-like language,
in the end led to _less_ efficient code.  Draw your own conclusions about
implications for teaching.

-- 
Australian citizen since 14 August 1996.  *Now* I can vote the xxxs out!
Richard A. O'Keefe; http://www.cs.rmit.edu.au/~ok; RMIT Comp.Sci.