CS 403: Programming Languages

Lecture 15

Fall 2003

Department of Computer Science

University of Alabama

Joel Jones

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Overview

Announcements Homework Minilanguages

Preliminaries—data formats Taxonomy of Minilanguages Case Studies

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Minilanguage

Definition—little language specialized for a particular application domain

A good notation has a subtlety and suggestiveness which at times makes it almost seem like a live teacher. —Bertrand Russell The World of Mathematics (1956)

Pair Up:

• Why use a minilanguage ?

Hint: Error rates are largely independent of the language used.

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Data Formats Programs store and retrieve data

from files and/or transmit data to another program, via a network or some other mechanism.

But, what should the format be? Binary–fast, but inflexible Textual–flexible, but slow(?)

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But what distinguishes text from binary?

Pair Up:

• List differences between a text format and a binary format

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On the importance of being textual Flexible, but what does that mean?

Not brittle, allows for future changes in the format/contents

Pair Up:

• What happens if larger numbers are needed in a binary format? In a text format?

We’ll examine the issue of speed later

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Styles (metaformats) of structuring textual data Delimiter separated value

Example, Unix passwd file:

games:*:12:100:games:/usr/games:gopher:*:13:30:gopher:/usr/lib/gopher-data:ftp:*:14:50:FTP User:/home/ftp:esr:0SmFuPnH5JlNs:23:23:Eric S. Raymond:/home/esr:nobody:*:99:99:Nobody:/:

Colons are allowed inside fields by using escape mechanism: \: Much better than quoting mechanism used by

various CSV files from Microsoft–quotes within quotes

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Textual works for protocols also

SMTP: Simple Mail Transfer Protocol Used to send mail

C: <client connects to service port 25> C: HELO snark.thyrsus.com sending host identifies self S: 250 OK Hello snark, glad to meet you receiver acknowledges C: MAIL FROM: <esr@thyrsus.com> identify sending user S: 250 <esr@thyrsus.com>... Sender ok receiver acknowledges C: RCPT TO: cor@cpmy.com identify target user S: 250 root... Recipient ok receiver acknowledges C: DATA S: 354 Enter mail, end with "." on a line by itself C: Scratch called. He wants to share C: a room with us at Balticon. C: .end of multiline send S: 250 WAA01865 Message accepted for delivery C: QUIT sender signs off S: 221 cpmy.com closing connection receiver disconnects C: <client hangs up>

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Taxonomy of minilanguages

/etc/passwdYaccmakeXSLT awk

Postscript

Data Formats Minilanguages Interpreters

Less to more generaldeclarative to imperative

Flat to structured

SNG regexps bc

JavaScriptsh Perl

PythonJava

Increasing Loopiness

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Case Studies

Performed live on stage! The following demo will be captured using script, a Unix command that captures input and output

Using a shell as glue Pipes and filters Wrappers vs. programs

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Case Studies: Regular Expressions . Matches any single

character * Matches zero or more

copies of the preceding expression

[] Character class which matches any character within the brackets. If it starts with a circumflex ‘^’ negates test. A dash indicates a range

^ Matches the beginning of a line

$ Matches the end of a line \ escapes metacharacters e.g.

“\n” is a newline character, “\*” is a literal asterisk

+ Matches one or more occurrences

? Matches zero or one occurences

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Regular Expression (Continued) | Matches either the

regular expression before or after

“…” Interprets everything inside quotes literally

() Groups a series of regular expression together into a new regular expression