6 Tangle

6 Tangle

If the scanner, parser, and analyser have successfully (i.e. with

no errors, severe errors, or fatal errors) completed, and the

Tutorial

Tangle option (+O) is turned on (it is by default), then the

Tangle component of FunnelWeb is invoked to generate the

Developer

product files specified in the @O macros of the input file.

The operation of Tangle is very simple. Each @O macro is

Reference

expanded and written to a file of the same name. As there are a

1 Introduction

finite number of macros, and the analyser guarantees that the

2 Interface

macro structure is non recursive, Tangle is guaranteed to

3 Scanner

terminate.

4 Parser

Three remaining points are worth mentioning.

5 Analyser

Tangle expands macros using blank indentation unless

G   

6 Tangle

the user has specified otherwise in an indentation pragma

7 Weave

in the input file.

8 Shell

Tangle keeps track of the length of the lines that it is

G   

9 Commands

writing and issues an error if any line of any product file

10 Glossary

that it generates is longer than the maximum. The

11 References

maximum is the minimum of a value defaulted or

specified in the input file, and the value (if any) provided

SEARCH

by the +w command line argument.

If there is more than one macro definition of the same

G   

name, then each such definition must have a different

library level (@L). Tangle uses the macro definition that

has the lowest library level and ignores the others

completely.

Memory Use During Tangling

When FunnelWeb executes, it reads each input file (the main

input file and any include files) into memory where they are

kept for the duration of the run. This means that there must be

room in memory for all of the input files. This approach is

necessary to support FunnelWeb s unrestricted forward

referencing.

In contrast, there is no requirement that there be enough

memory to hold the product files, as these are written to disk

sequentially during their expansion. Furthermore, FunnelWeb

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