Appendix C  Core Predicates

• Modules
• Predicate definition
• Control
• I/O
• Arrays
• Hash Tables
• Arithmetic
• Terms and structures
• List Handling

This section lists essential ECLiPSe built-in and library predicates. These predicates are used in most applications, and should be well understood. There are more than 1000 other built-in and library predicates which are required for specific tasks only.

C.1  Modules

module directive

define a module

export directive

make predicates available outside a module

use_module directive

make predicates from other module available

lib directive

make predicates from library available

:

call a predicate from a particular module

C.2  Predicate definition

mode directive

define input/output modes for a predicate

comment directive

define comments about a module or a predicate

C.3  Control

,

conjunction, and

;

disjunction, or

->

implication, if-then-else together with disjunction

!

cut, remove choices

call/1

call argument as a predicate call

once/1

call argument as a predicate call, find one solution only

not/1

negation, fail if call to argument succeeds

true/0

always succeed, empty predicate definition

block/3

define a block in order to catch exceptions

exit_block/1

jump out of a block

C.3.1  Do Loops

do

general iteration operator

foreach

iterate over each element in a list

foreacharg

iterate over each argument of a term

fromto

accumulator argument

for

iterate over all integers between two bounds

param

declare parameter variables which are passed into the do-loop

C.4  I/O

exists/1

succeeds if a file exists

open/3

open a file or a string as a stream

close/1

close a stream

write/2

write some term to a stream

nl/1

write a new-line to a stream

writeln/2

write a term to a stream, followed by a new-line

writeq/2

write a term in canoncial form, so that if can be read back

read/2

read a term from a stream

read_string/4

read a string from a stream

concat_string/2

build a string from a list of components

phrase/3

call DCG analyzer

read_exdr/2

read a term from a file in EXDR format

write_exdr/2

write a term to a file in EXDR format

flush/1

flush an output stream

C.5  Arrays

dim/2

define an array; can also be used to find size of an array

subscript/3

get an element of an array

C.6  Hash Tables

hash_create/1

create a hash table

hash_add/3

add an item to a hash table

hash_find/3

find if an item is in a hash table

C.7  Arithmetic

is/2

evaluate term

=:= /2

evaluate two terms and compare for equality

=\= /2

evaluate two terms and compare for disequality

>/2

evaluate two terms and compare for inequality

>= /2

evaluate two terms and compare for inequality

</2

evaluate two terms and compare for inequality

=</2

evaluate two terms and compare for inequality

C.8  Terms and structures

struct/1

define named structure

with

access element(s) in named structure

of

find argument position in named structure

functor/3

define/analyze term for functor and arity

arg/3

access argument of term

compare/3

compare two terms for lexicographical order

= /2

two terms can be unified

== /2

two terms are identical

\= /2

two terms cannot be unified

number/1

argument is a number

integer/1

argument is an integer

atom/1

argument is an atom

var/1

argument is a variable

string/1

argument is a string

real/1

argument is a float

compound/1

argument is a term

C.9  List Handling

sort/2/4

sort a list

memberchk/2

check if an item occurs in a list

length/2

find the length of a list or create a list with given length

findall/3

find all solutions to a query and return a list of all answers