Lexical Elements of the DEC Text Processing Utility Language 4.8 Expressions

When used with markers, these operators test whether one marker is closer to (or farther from) the top of the buffer than another marker. (If markers are in different buffers, they will return as false.) For example, the procedure in Example 4–3 uses relational operators to determine which half of the buffer the cursor is located in.

Example 4–3 Procedure That Uses Relational Operators on Markers

PROCEDURE which_half

LOCAL number_lines, saved_mark;

saved_mark := MARK (FREE_CURSOR);

POSITION (BEGINNING_OF (CURRENT_BUFFER));

number_lines := GET_INFO (current_buffer, "record_count"); IF number_lines = 0

THEN

MESSAGE ("The current buffer is empty");

ELSE

MOVE_VERTICAL (number_lines/2);

IF MARK (FREE_CURSOR) = saved_mark

THEN

MESSAGE ("You are at the middle of the buffer");

ELSE

IF MARK (FREE_CURSOR) < saved_mark

THEN

MESSAGE ("You are in the second half of the buffer");

ELSE

MESSAGE ("You are in the first half of the buffer");

ENDIF;

ENDIF;

ENDIF;

ENDPROCEDURE;

4.8.3 Pattern Expressions

A pattern expression consists of the pattern operators (+, &, , @) combined with string constants, string variables, pattern variables, pattern procedures, pattern keywords, or parentheses. The following are valid pattern expressions:

pat1 := LINE_BEGIN + SPAN ("0123456789") + ANY ("abc"); pat2 := LINE_END + ("end""begin");

pat3 := SCAN (’;"!’) + (NOTANY ("’") & LINE_END);

See Chapter 3 for more information on pattern expressions.

4.8.4 Boolean Expressions

DECTPU performs bitwise logical operations on Boolean expressions. This means that the logical operation is performed on the individual bits of the operands to produce the individual bits of the result. In the following example, the value of user_variable is set to 3.

user_variable := 3 AND 7;

As another example, if user_var were %X7777 (30583), then you would use the following statement to set user_var to %x0077 (119):

user_var := user_var AND %XFF

Lexical Elements of the DEC Text Processing Utility Language 4–11

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Compaq AA-PWCBD-TE manual Pattern Expressions, Boolean Expressions
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