48 lines
891 B
Go
48 lines
891 B
Go
// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
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// All rights reserved.
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// operator-fact.go
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package expr
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import "fmt"
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//-------- fact term
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func newFactTerm(tk *Token) (inst *term) {
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return &term{
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tk: *tk,
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children: make([]*term, 0, 1),
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position: posPostfix,
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priority: priFact,
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evalFunc: evalFact,
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}
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}
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func evalFact(ctx ExprContext, opTerm *term) (v any, err error) {
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var leftValue any
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if leftValue, err = opTerm.evalPrefix(ctx); err != nil {
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return
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}
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if IsInteger(leftValue) {
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if i, _ := leftValue.(int64); i >= 0 {
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f := int64(1)
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for k := int64(1); k <= i; k++ {
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f *= k
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}
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v = f
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} else {
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err = fmt.Errorf("factorial of a negative integer (%d) is not allowed", i)
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}
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} else {
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err = opTerm.errIncompatibleType(leftValue)
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}
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return
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}
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// init
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func init() {
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registerTermConstructor(SymExclamation, newFactTerm)
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}
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