117 lines
1.8 KiB
Go
117 lines
1.8 KiB
Go
package main
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import (
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"fmt"
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"os"
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)
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var source = `
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(+ 1 2 3 4)
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`
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func (v *Value[T]) Step() (Expression, error) {
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return v, nil
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}
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func (v *Quoted) Step() (Expression, error) {
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return v, nil
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}
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func (d *Declaration) Step() (Expression, error) {
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return &Value[int]{0}, nil
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}
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func (v *Identifier) Step() (Expression, error) {
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switch v.value {
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case "+":
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f := func(args []Expression) (Expression, error) {
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sum := 0
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for _, arg := range args {
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if !isValue(arg) {
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panic("!")
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}
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switch x := arg.(type) {
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case *Value[int]:
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sum += x.value
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case *Value[*Int]:
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sum += x.value.value
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default:
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return nil, fmt.Errorf("invalid type")
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}
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}
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return &Value[int]{sum}, nil
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}
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return &Value[Function]{f}, nil
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default:
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panic("!")
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}
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}
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func (v *List) Step() (Expression, error) {
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for i, expr := range v.els {
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if !isValue(expr) {
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e, err := expr.Step()
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if err != nil {
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return nil, err
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}
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v.els[i] = e
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return v, nil
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}
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}
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if len(v.els) == 0 {
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return nil, fmt.Errorf("empty list")
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}
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f, ok := v.els[0].(*Value[Function])
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if !ok {
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return nil, fmt.Errorf("not a function")
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}
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r, err := f.value(v.els[1:])
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if err != nil {
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return nil, err
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}
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return r, nil
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}
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func isValue(e Expression) bool {
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switch e.(type) {
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case *Value[int], *Value[*Int], *Value[Function], *Quoted:
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return true
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default:
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return false
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}
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}
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func fullStep(e Expression) (Expression, error) {
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for !isValue(e) {
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n, err := e.Step()
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if err != nil {
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return n, nil
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}
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e = n
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}
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return e, nil
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}
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func main() {
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if len(os.Args) > 1 {
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source = os.Args[1]
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}
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tk, err := lex(source)
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if err != nil {
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panic(err)
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}
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p, err := consume(tk)
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if err != nil {
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panic(err)
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}
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s, err := p.Step()
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if err != nil {
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panic(err)
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}
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result, err := fullStep(s)
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if err != nil {
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panic(err)
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}
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fmt.Println(result)
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}
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