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82 lines
1.8 KiB
Go
82 lines
1.8 KiB
Go
package main
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import (
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"fmt"
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"reflect"
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)
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// type accumulator describes an accumulator. That is, it is a numerical
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// structure that applies a pair of functions across a list of values that are
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// expected to be numerical; i.e. of type int64 or float64.
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type accumulator struct {
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name string
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floatFn func(float64, float64) (float64, error)
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intFn func(int64, int64) (int64, error)
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acc int64
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accf float64
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floating bool
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}
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// runs the accumulator accros the set of values, applying the accumulator's
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// intFn and floatFn functions in order. It's basically just a left fold, and
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// it starts using floatFn once the first float value is encountered, and then
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// thereafter.
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func (a accumulator) total(vals []interface{}) (interface{}, error) {
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if vals == nil || len(vals) == 0 {
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return a.acc, nil
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}
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switch v := vals[0].(type) {
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case int64:
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a.acc = v
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case float64:
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a.floating = true
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a.accf = v
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default:
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return nil, fmt.Errorf("%v is not defined for %v", a.name, reflect.TypeOf(v))
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}
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if len(vals) == 1 {
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if a.floating {
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return a.accf, nil
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} else {
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return a.acc, nil
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}
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}
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for _, raw := range vals[1:] {
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switch v := raw.(type) {
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case int64:
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var err error
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if a.floating {
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a.accf, err = a.floatFn(a.accf, float64(v))
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} else {
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a.acc, err = a.intFn(a.acc, v)
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}
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if err != nil {
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return nil, err
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}
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case float64:
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var err error
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if a.floating {
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a.accf, err = a.floatFn(a.accf, v)
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} else {
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a.floating = true
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a.accf, err = a.floatFn(a.accf, float64(a.acc))
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}
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if err != nil {
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return nil, err
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}
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default:
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return nil, fmt.Errorf("%v is not defined for %v", a.name, reflect.TypeOf(v))
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}
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}
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if a.floating {
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return a.accf, nil
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} else {
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return a.acc, nil
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}
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panic("not reached")
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}
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