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expr_recursion.go
53 lines (45 loc) · 1.43 KB
/
expr_recursion.go
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package rel
import (
"fmt"
"github.com/arr-ai/wbnf/parser"
"github.com/go-errors/errors"
)
type RecursionExpr struct {
ExprScanner
name Pattern
fn Expr
fix, fixt Value
}
func NewRecursionExpr(scanner parser.Scanner, name Pattern, fn Expr, fix, fixt Value) Expr {
return RecursionExpr{ExprScanner{scanner}, name, fn, fix, fixt}
}
func (r RecursionExpr) Eval(local Scope) (Value, error) {
name, isIdent := r.name.(ExprPattern).Expr.(IdentExpr)
if !isIdent {
return nil, wrapContext(errors.Errorf("Does not evaluate to a variable name: %v", r.name), r, local)
}
val, err := r.fn.Eval(local)
if err != nil {
return nil, wrapContext(err, r, local)
}
//TODO: optimise, get it to load either fix or fixt not both
switch f := val.(type) {
case Tuple:
t := f
for e := f.Enumerator(); e.MoveNext(); {
attr, val := e.Current()
if fn, isFunction := val.(Closure); isFunction {
f = f.With(attr, NewClosure(local, NewFunction(fn.Source(), name, fn.f).(*Function)))
continue
}
return nil, wrapContext(errors.Errorf("Recursion requires a tuple of functions: %v", t.String()), r, local)
}
return Call(r.fixt, f, local)
case Closure:
return Call(r.fix, NewClosure(local, NewFunction(f.Source(), name, f.f).(*Function)), local)
}
return nil, wrapContext(errors.Errorf("Recursion does not support %T", val), r, local)
}
func (r RecursionExpr) String() string {
return fmt.Sprintf("\\%s %s", r.name, r.fn)
}