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// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Paul Buetow
package rpn
import (
"strings"
)
// stack manipulation operators
// Dup duplicates the top stack value.
func (o *Operations) Dup(stack *Stack) error {
val, err := stack.Peek()
if err != nil {
return buildError("dup", err)
}
stack.Push(val)
return nil
}
// Swap swaps the top two stack values.
func (o *Operations) Swap(stack *Stack) error {
if err := ensureStackLength(stack, 2, "swap"); err != nil {
return err
}
top, _ := stack.Pop()
second, _ := stack.Pop()
stack.Push(top)
stack.Push(second)
return nil
}
// Pop removes and discards the top stack value.
func (o *Operations) Pop(stack *Stack) error {
if _, err := stack.Pop(); err != nil {
return buildError("pop", err)
}
return nil
}
// Show returns the current stack as a formatted string.
// Each value uses its StackValue.String() method for display.
// Numeric values with non-Universal metrics append the metric suffix (e.g., "100Mbps").
// Values with the Universal metric (Cool) display without a suffix.
// Booleans display as "true"/"false". Symbols display with a leading ":" prefix.
func (o *Operations) Show(stack *Stack) (string, error) {
if stack.Len() == 0 {
return "Stack is empty", nil
}
vals := stack.Values()
var sb strings.Builder
for i, val := range vals {
if i > 0 {
sb.WriteByte(' ')
}
// Append metric suffix for non-Cool metrics
m := val.Metric()
if m != nil && m.Category != Universal {
sb.WriteString(val.String())
sb.WriteString(m.Name)
} else {
sb.WriteString(val.String())
}
}
return sb.String(), nil
}
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