JavaScript and Prolog are both dynamically typed languages. The WASM module defines a faithful translation between JavaScript data and Prolog data that aims at completeness as well as keeping the data representation clean in the common cases. We describe the translation in two descriptions because round tripping does not always result in the original object.
This section describes how data from JavaScript is translated into Prolog. The interface is primarily designed for passing JavaScript data as typically used to a natural Prolog representation. In addition a number of classes are provided to create Prolog specific data structures such as strings (as opposed to atoms), variables, compound terms, etc.
new Prolog.String(text)
to create a Prolog string. See below.true or false.undefined.null.$:Typev holds the text. May be
created using new Prolog.string(text). May be created using new
Prolog.String(text).n and d
represent the numerator and denominator. For example,
to represent 1r3, use {$:"r",
n:1, d:3}. May be created using new
Prolog.Rational(n, d), where n and d can be
JavaScript numbers or big integers.point(1,2) is constructed using
{$:"t", point:[1,2]}. May be created using new
Prolog.Compound(functor, args)v is present this
identifies the variable. Two variables processed in the same translation
with the same identifier represent the same Prolog variable. If the v
key is omitted the variable will be unique. May be created using new
Prolog.Var(id).Array we only need
this typed object to create a partial list. The v
key contains the “normal” elements and the key tail
contains the tail of the list. May be created using new
Prolog.List(array, tail).Objectdict.
Note that JavaScript object keys are always strings and (thus) all dict
keys are atoms. This, {1:"one"} is translated into
_{'1': one}.ArrayBuffer are translated into a Prolog
string that consists of characters in the range 0 ... 255.Object<js_Class(id)>. The
Prolog interface allows for passing the objects back and calling methods
on them. See section
13.3.
Most of the translation from Prolog data to JavaScript is the reverse
of the translation described in section
13.2.2.1. In some cases however reverse translation is ambiguous.
For example, both
42 and 42n (a JavaScript BigInt)
translate to a simple Prolog integer. The other way around, as
JavaScript
Number is a float, both Prolog 42 and 42.0
translate to 42 in JavaScript.
Prolog.Variable instance where
the identifier is a unique number of each unique variable.Number when possible or
BigInt otherwise. Currently JavaScript Number
can represent integers upto 2^53 precisely.Prolog.Rational instance.Number.String.Prolog.String instance.Array,
otherwise create a JavaScript Prolog.List instance.Prolog.Compound instance.Object with the same keys. If the
dict has a non-var tag, add a $tag property.