106 lines
2.4 KiB
Go
106 lines
2.4 KiB
Go
package lang
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import (
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"fmt"
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"reflect"
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"strings"
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)
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// Term is a unit of language which carries some meaning. Some Terms are
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// actually comprised of multiple sub-Terms.
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type Term interface {
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fmt.Stringer // for debugging
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// Type returns a Term which describes the type of this Term, i.e. the
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// components this Term is comprised of.
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Type() Term
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}
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// Equal returns whether or not two Terms are of equal value
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func Equal(t1, t2 Term) bool {
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return reflect.DeepEqual(t1, t2)
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}
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////////////////////////////////////////////////////////////////////////////////
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// Atom is a constant with no other meaning than that it can be equal or not
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// equal to another Atom.
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type Atom string
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func (a Atom) String() string {
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return string(a)
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}
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// Type implements the method for Term
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func (a Atom) Type() Term {
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return Atom("atom")
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}
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////////////////////////////////////////////////////////////////////////////////
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// Const is a constant whose meaning depends on the context in which it is used
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type Const string
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func (a Const) String() string {
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return string(a)
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}
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// Type implements the method for Term
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func (a Const) Type() Term {
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return Const("const")
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}
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////////////////////////////////////////////////////////////////////////////////
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// Tuple is a compound Term of zero or more sub-Terms, each of which may have a
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// different Type. Both the length of the Tuple and the Type of each of it's
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// sub-Terms are components in the Tuple's Type.
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type Tuple []Term
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func (t Tuple) String() string {
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ss := make([]string, len(t))
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for i := range t {
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ss[i] = t[i].String()
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}
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return "(" + strings.Join(ss, " ") + ")"
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}
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// Type implements the method for Term
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func (t Tuple) Type() Term {
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tt := make(Tuple, len(t))
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for i := range t {
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tt[i] = t[i].Type()
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}
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return Tuple{Atom("tup"), tt}
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}
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////////////////////////////////////////////////////////////////////////////////
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type list struct {
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typ Term
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ll []Term
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}
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// List is a compound Term of zero or more sub-Terms, each of which must have
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// the same Type (the one given as the first argument to this function). Only
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// the Type of the sub-Terms is a component in the List's Type.
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func List(typ Term, elems ...Term) Term {
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return list{
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typ: typ,
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ll: elems,
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}
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}
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func (l list) String() string {
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ss := make([]string, len(l.ll))
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for i := range l.ll {
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ss[i] = l.ll[i].String()
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}
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return "[" + strings.Join(ss, " ") + "]"
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}
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// Type implements the method for Term
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func (l list) Type() Term {
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return Tuple{Atom("list"), l.typ}
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}
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