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Language Processing Language, Unread Function Definition

IP.com Disclosure Number: IPCOM000108249D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Hidalgo, DS: AUTHOR

Abstract

Disclosed is a feature of the LANGUAGE PROCESSING LANGUAGE (LPL) that supports the interfacing of a Lexical Scanner mechanically generated from an LDF (Language Definition File) with manually written code to form a translator for a formal language. The technique used by the LPL mechanically generated Lexical Scanner requires that characters be read ahead of their use in order to determine the symbol boundaries within the input source stream. As a result, it is often necessary during the scanning process to "unread" one or two characters after they have been read by the Lexical Scanner.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Language Processing Language, Unread Function Definition

       Disclosed is a feature of the LANGUAGE PROCESSING
LANGUAGE (LPL) that supports the interfacing of a Lexical Scanner
mechanically generated from an LDF (Language Definition File)  with
manually written code to form a translator for a formal language. The
technique used by the LPL mechanically generated Lexical Scanner
requires that characters be read ahead of their use in order to
determine the symbol boundaries within the input source stream. As a
result, it is often necessary during the scanning process to "unread"
one or two characters after they have been read by the Lexical
Scanner. When a character is "unread" by the Lexical Scanner, the
latter calls a function that abstracts the "unread" operation as one
of logically returning the "unread" character to the Input Source so
that it again becomes the character read the next time the Read
Function is called by the Lexical Scanner.

      When the Input Source of the formal language translator is a
file, the LPL mechanically generated code references a default Unread
Function. However, if the Input Source is a main memory buffer the
LPL user must provide a manually written Unread Function. In order to
provide maximum design flexibility, LPL must provide the necessary
interfacing mechanism between the manually written Unread Function
and the mechanically generated code. Such mechanism is, in fact,
essential in abstracting the Input Source from the alg...