Turbo_Prolog_Owners_Handbook_1987

containing this call. This predicate can be used in conjunction with (tlepos to update a random access file.

openread(SymbolicFileName, DosFileName) (file,string) : (i,i)

Opens the disk file DosFileName for reading, and attaches the SymbolicFileName to that file for future reference within the Turbo Prolog program containing this call.

openwrite(SymbolicFileName,DosFileName) (file,string) : (i,i)

Opens the disk file DosFileName for writing and attaches the SymbolicFileName to that file for future reference within the Turbo Prolog program containing this call. If a file called DosFileName already exists on the disk, it is deleted.

Determines the Color of the trail left by the pen. For the standard Color/Graphics Adapter, the color is determined according to Table 7-1.

pendown

Activates the pen used by the forward and back predicates.

penup

De-activates the pen used by the forward and back predicates.

(1,0)

Binds Value to the decimal equivalent of the byte value at I/O port PortNo.

(1,1)

Sends the Value to I/O port PortNo.

ptr_dword(StringVar, Segment,Offset)

(string,integer,integer) : (i,o,o) (o,i,i)

(1,0,0)

When StringVar is bound, ptr_word returns the internal Segment and Offset address of

StringVar.

(0,1,1)

When Segment and Offset are bound, ptLword returns the contents of location Segment* 16 +Offset and following as a string. The string consists of the characters with the given ASCII values and is terminated at the first location containing a NUL byte (i.e., a byte set to 0).

Reads a single character from the current read device (the keyboard unless the default is changed via readdevice).

(1)

Reassigns the current read device to the file opened with the given SymbolicFileName, which may be the pre-defined symbolic file keyboard or any user-defined symbolic file name for a file opened for reading or modifying.

(0)

Binds SymbolicFileName to the name of the current read device, which may be the predeclared keyboard or a file (see, for example, openread).

readint(IntVariable) (integer) : (0)

Reads an integer from the current read device (the keyboard unless the default is changed via readdevice) terminated by an ASCII carriage-return character.

readln(StringVariable) (string) : (0)

Reads characters from the current read device (the keyboard unless the default is changed via readdevice) until an ASCII carriage-return character is read.

readreal(ReaIVariable) (real) : (0)

Reads a real from the current read device (the keyboard unless the default is changed via readdevice) terminated by an ASCII carriage-return character.

readterm(Domain,Term) (name),(variable») : (o,i)

Reads any object written by the write predicate. Term is bound to the object read, provided it conforms with the declaration of Domain. readterm allows facts to be accessed on files.

removewindow

Removes the currently active window from the screen.

renamefile(OldDosFileName,NewDosFileName)

(string, string) : (i,i)

Renames the file OldDosFileName (on the currently accessed disk) to NewDosFileName.

Deletes the first (fact) in the database that matches the given (fact).

(i)

Turns the turtle the indicated Angle (in degrees) to the right (clockwise).

(0)

Binds Angle to the current direction of the turtle.

Saves all the clauses for database predicates in the text file to which DOSFileName refers. save saves a fact on each line in the file. The file can later be read into memory by the consult predicate. The text file-and thus the entire database, can also be inspected and manipulated using the editor.

scr_attr(Row, Col,Attr) (integer,integer,integer) : (i,i,i) (i,i,o)

(1,1,1)

Sets the attribute of the character at screen position Row, Col to the value referred to by Attr.

(i,i,o)

Returns the value of the attribute setting for the character at position Row, Col.

scr_char(Row,Column,Char) (integer,integer,char) : (i,i,i) (i,i,o)

(i,i,1)

Writes the character Char on the screen with the current attribute at the position given by Rowand Column.

(i,i,o)

Reads a character from the specified position.

(i)

Changes the currently active window to the one referred to by WindowNo. (Any previously active window is stored in its current state.) The cursor returns to the position it was in when window WindowNo was last active.

(0)

Binds WindowNo to the number of the currently active window.

Plays a note through the speaker with given Frequency for Duration hundredths of a second.

storage(StackSize,HeapSize,TrailSize) (real,real,real) : (0,0,0)

Returns the available size of the three run-time memory areas used by the Turbo Prolog system.

(i,o)

Binds ChorPoram to the single character contained in the string to which StringPorom is bound.

(o,i)

Binds StringPoram to the character specified by ChorPoram.

(i,i)

Succeeds if ChorPoram and StringPoram are both bound to representations of the same character.

str-int(StringParam,IntParam) (string,integer) : (i,o) (o,i) (i,i)

(i,o)

Binds IntPoram to the internal (binary) equivalent of the decimal integer to which

StringPoram is bound.

(o,i)

Binds StringPoram to a string of decimal digits representing the value to which IntPorom is bound.

(i,i)

Succeeds if IntPoram is bound to the internal (binary) representation of the decimal integer to which StringPoram is bound.

(i,i)

Succeeds if String has Length characters.

(i,o)

Succeeds by binding Length to the number of characters in String.

(i,o)

Binds ReolPoram to the internal (binary) equivalent of the decimal real number to which

StringPoram is bound.

(o,i)

Binds StringPoram to a string of the decimal digits representing the value to which

ReolPoram is bound.

(i,i)

Succeeds if ReolPoram is bound to the internal (binary) representation of the decimal real number represented by the string to which StringPoram is bound.

(i)

Sends DosCommandString to DOS for execution.

text

Resets the screen in text mode. The call has no effect if the screen was already in text mode.

time(Hours,Minutes,Seconds,Hundredths)

(integer,integer,integer,integer) : (i,i,i,i) (0,0,0,0)

(i,i,i,i)

Sets the time used by the computer's internal clock.

(0,0,0,0)

Reads the time from the computer's internal clock.

( i)

trace(on) turns tracing on (in whichever mode has been selected by the corresponding compiler directive-trace or shorttrace); trace(off) turns tracing off.

(0)

Binds Status to on or off. indicating whether tracing is being performed or not.

upper-Iower(StringlnUpperCase, StringlnLowerCase) (string,string) : (i,i) (i,o) (o,i)

(i,o)

Binds StringlnLowerCase to the lowercase equivalent of the string to which StringlnUpperCase is bound.

(o,i)

Binds StringlnUpperCase to the uppercase equivalent of the string to which StringlnLowerCase is bound.

(i,i)

Succeeds if StringlnLowerCase and StringlnUpperCase are bound to lower and uppercase versions of the same string.

Gives the currently active window the attribute value to which Attr is bound.

(i)

Binds ScreenString to the string currently displayed in the active window; therefore ScreenString has the same number of lines as there are lines in the active window. The length of each line is determined by the last non-blank character in that line.

(0)

ScreenString is written in the window according to the following criteria:

•If there are more lines in the string than there are lines in the window, lines will be written until the window space is exhausted.

•If there are fewer lines in the string than in the window, the remaining lines in the window will be filled out with blank spaces.

•If there are more characters on a string line than are available on a window line, the string line will be truncated to fit.

•If there are fewer characters in a line than there are columns in the window, the line will be filled out with blank spaces.

write( el,e2,e3, ... ,eN)

Writes the given constants or values in the currently active window on the current writedevice. Can be called with an optional number of arguments ei, which can either be constants or variables bound to values of the standard domain types.

(i)

Reassigns the current writedevice to the file opened with the given SymbolicFileName, which may be one of the predefined symbolic files (screen and printer) or any userdefined symbolic filename for a file opened for writing or modifying.

(0)

Binds SymbolicFileName to the name of the current writedevice, which may be the predeclared screen or printer, or a file (see, for example, openwrite).

Produces formatted output. Arg I to ArgN must be constants or variables that belong to domains of standard type. The format string contains ordinary characters, which are printed without modification, and format specifiers of the form:

%-m.p

• "_" indicates left justification; right justification is the default.

•The optional m field specifies the minimum field width.

•The optional .p field determines the precision of a floating-point image (or the maximum number of characters to be printed from a string). This field can also contain one of the letters f, ~ or g denoting:

f - Reals in fixed decimal notation (default). e - Reals in exponential notation.

g - Use the shortest format.

COMPILER DIRECTIVES

BNF SYNTAX FOR TURBO PROLOG

The following BNF notation is used to define Turbo Prolog syntax:

Names

A Turbo Prolog (name) is defined by

<name> ::= «letter> ! _ ) { <letter> <digit>! }*

(name)s must start with a letter or an underscore, followed by a contiguous sequence of letters, digits and underscore characters. A list of names separated by commas is defined by

Note that a leading capital letter (or underscore) denotes a variable and a leading small letter denotes a constant.

Program Section

<predicate section> <clause section> <goal section> <database section> <include-directive>

(This syntax is subject to the restrictions on program sections.)

Directives

Domains Section

Predicate and Database Section

<database-section> ::= database { <predicate-def>}*

Clause Section