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package main
import (
"math/rand"
"strings"
)
func first(s, arg string) agg { return &sbinop{s, opfirst} }
func last(s, arg string) agg { return &sbinop{s, oplast} }
func prefix(s, arg string) agg { return &sbinop{s, opprefix} }
func join(s, arg string) agg { return &sbinop{s, opjoin(arg)} }
func smin(s, arg string) agg { return &sbinop{s, opsmin} }
func smax(s, arg string) agg { return &sbinop{s, opsmax} }
type sbinop struct {
s string
f func(a, b string) string
}
func (o *sbinop) String() string { return o.s }
func (o *sbinop) merge(s string) { o.s = o.f(o.s, s) }
func opfirst(a, b string) string { return a }
func oplast(a, b string) string { return b }
func opprefix(a, b string) string {
for i := range a {
if i >= len(b) || a[i] != b[i] {
return a[:i]
}
}
return a
}
func opjoin(sep string) func(a, b string) string {
return func(a, b string) string {
return a + sep + b // TODO(kr): too slow? maybe strings.Join?
}
}
func opsmin(a, b string) string {
if strings.Compare(a, b) <= 0 {
return a
}
return b
}
func opsmax(a, b string) string {
if strings.Compare(a, b) >= 0 {
return a
}
return b
}
type sampler struct {
n int
s string
}
func sample(s, arg string) agg { return &sampler{1, s} }
func (p *sampler) String() string { return p.s }
func (p *sampler) merge(s string) {
p.n++
if rand.Intn(p.n) == 0 {
p.s = s
}
}
type constant string
func constf(init, arg string) agg { return constant(arg) }
func (c constant) String() string { return string(c) }
func (c constant) merge(string) {}
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