git ssb

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'use strict'
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var drain = require('./drain')
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module.exports = function reduce (reducer, acc, cb ) {
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  if(!cb) cb = acc, acc = null
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  var sink = drain(function (data) {
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    acc = reducer(acc, data)
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  }, function (err) {
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    cb(err, acc)
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  })
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  if (arguments.length === 2)
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    return function (source) {
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      source(null, function (end, data) {
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        //if ended immediately, and no initial...
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        if(end) return cb(end === true ? null : end)
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        acc = data; sink(source)
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      })
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    }
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  else
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    return sink
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}
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