An Exercise In Writing

(comments are still off)

I am making an effort to improve my writing. Here is a sample of what I have been doing.

In the following exercise, I take a murky paragraph(from EssentialsOf Programming Languages, First Edition,Chapter 8, "Continuation Passing Style") and try to systematically make it clearer. (The technical content of the passage is irrelevant. I am concerned here with sentence and paragraph structure).

The original paragraph

1."We have seen how interpreters can be used to model and explain the behaviour of programming languages. The explicit treatment of environments serves to explain scope and identifier lookup rules and the modelling of procedures as closures explains how procedures use lexical scope to make their behaviour independent of the environment in which they are invoked. Our interpreters are written in scheme, but are suitable for implementation in many other languages because they use ordinary data structures and procedure calls."

Getting rid of the nominalizations and passives gives

2." In previous chapters we learned how interpreters model and explain programming language behaviour. First, we focussed explicitly on environments to understand scope and the rules for identifier lookup. Then we modelled procedures as closures to understand how lexical scope enables procedures to have behaviour independent of the environments in which we invoke them. So far, we wrote the interpreters in scheme, but we could use many other languages because they all use ordinary data structures and procedure calls."

Splitting off the "writing in scheme" idea is into its own paragraph, and eliminating the irrelevant sequencing gives

3."Writing Interpreters is the best way to model programming languages and learn how they behave. When we focus explicitly on environments, we understand how scoping and identifier lookup works. If we model procedures as closures, we can understand how lexical scoping enables a procedure to have behaviour distinct from the environments in which we invoke them.

So far, we wrote the interpreters in scheme, but we could use many other languages because they all use ordinary data structures and procedure calls."

Now there is a concept gap evident between the first and second lines. Plugging that gap and rewriting the 3d sentence to eliminate the irrelevant "we", we get

4. "Interpreters model programming languages and explain their behaviour.To understand language features we need to study the structure of interpreters implementing those features.If we focus on environments, we understand scoping and identifier lookup. Modelling procedures as closures clarifies how lexical scoping makes the behaviour of a proceudure independent of the environment in which we invoke it.

So far, we wrote the interpreters in scheme, but we could use many other languages because they all use ordinary data structures and procedure calls."

I don't like the phrases "(lexical closures) make the behaviour of procedures independent" and "environment in which we invoke". So I replace them.

5. Interpreters model programming languages and explain their behaviour.To understand language features we study the architecture of interpreters implementing those features.If we focus on environments, we understand scoping and identifier lookup. Modelling procedures as closures clarifies how lexical scoping frees a procedure's behaviour from its invocation environment.

So far, we wrote the interpreters in scheme, but we could use many other languages because they all use ordinary data structures and procedure calls."

Now the paragraph is as clean as I can make it, but so far I have treated it as a standalone chunk of text with no relation to the rest of the chapter. I fix that (these modifications depend on understanding what the author intends to teach in this chapter), and smooth away the abruptness of the second paragraph, and remove an ambigous "they" (they = interpreters? languages?) to get the final version

6. Interpreters model programming languages and explain their behaviour.To understand language features we study the architecture of interpreters implementing those features.

If we focus on environments, we understand scoping and identifier lookup. Modelling procedures as closures clarifies how lexical scoping frees a procedure's behaviour from its invocation environment. To study recursion, exceptions, and other language features involving transfer of control, we should study an interpreter that explicitly maps control flow using continuations.

So far, we wrote the interpreters in Scheme and they all use ordinary data structures and procedure calls. So we could, in theory, use many other languages. In practice, we .."

At this point, I can't think of anything else to do (well I could change the rhythm of the sentences to avoid a staccato effect. But here I am concerned with sentence clarity not rhythm). So I stop.