3.2 Special Sequences

3.2 Special Sequences

The scanner scans the input file from top to bottom, left to right, treating the

input as ordinary text (to be handed directly to the parser as a text token) unless

Tutorial

it encounters the 

special character

 which introduces a 

special sequence

. Thus,

the scanner partitions the input file into ordinary text and special sequences.

Developer

(Note: This sort of character is often referred to as the "escape character" or the

"control character" in other systems. However, as there is great potential to

Reference

confuse these names with the "escape" character (ASCII 27) and ASCII

"control" characters, the term "special" has been chosen instead. This results in

1 Introduction

the terms 

special character

  and 

special sequence

 .

2 Interface

3 Scanner

input_file = { ordinary_text | special_sequence }

4 Parser

5 Analyser

Upon startup, the special character is @, but it can be changed using the

6 Tangle

= special sequence. Rather than using 

7 Weave

whenever the special character appears, this document uses the default special

character "

@

" to represent the current special character. More importantly,

8 Shell

FunnelWeb s error messages all use the default special character in examples,

9 Commands

even if the special character has been changed.

10 Glossary

11 References

An occurrence of the special character in the input file introduces a special

sequence. The kind of special sequence is determined by the character following

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the special character. Only printable characters can follow the special character.

The following list gives all the possible characters that can follow the special

character, and the legality of each sequence. The first column gives the ASCII

number of each ASCII character. The second column gives the special sequence

for that character. The next column contains one of three characters: "

" means

that the sequence is illegal. "

S

" indicates that the sequence is a 

simple sequence

(with no attributes or side effects) that appears exactly as shown and is

converted directly into a token and fed to the parser. Finally, "

C

" indicates that

the special sequence is complex, possibly having a following syntax or

producing funny side effects.

ASC  SEQ  COMMENT

000       \

016        | Unprintable chars (illegal specials).

031       /

032  @      Illegal (space).

033  @!   C Comment.

034  @"   S Parameter delimeter.

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