R version of https://hackernoon.com/functional-computational-thinking-what-is-a-monad-2adea91154e

functional_prog_fun.R

# R version of 
#https://hackernoon.com/functional-computational-thinking-what-is-a-monad-2adea91154e
library(magrittr)
readLines("./file1") %>% readLines()

readFileCPS <- function(path, cb){
  cb(readLines(path))
}

composeCPS <- function(g,f){
  function(x, cb){
    g(x, function(y){
      f(y, function(z) cb(z))
    })
  }
}

composeCPS(readFileCPS, readFileCPS)('file1', print)


readFileHOF <- function(path){
  function(cb){
    readFileCPS(path, cb)
  }
}

composeHOF <- function(g,f){
  function(x){
    function(cb){
      g(x)(function(y) f(y)(cb))
    }
  }
}

composeHOF(readFileHOF, readFileHOF)('./file1')(print)


readFileEXEC <- function(path){
  return(
    list(
      exec = function(cb){
        readFileCPS(path, cb)
      }
    )
  )
}


composeEXEC <- function(g, f){
  function(x){
    list(
      exec = function(cb){
        g(x)$exec(function(y){
          f(y)$exec(cb)
        })
      }
    )
  }
}

composeEXEC(readFileEXEC, readFileEXEC)('file1')$exec(print)


# Original

createExecObj <- function(exec){
  list(
    exec = exec,
    bind = function(f){
      createExecObj(
        function(cb){
          exec(function(y){
            f(y)$exec(cb)
          })
        }
      )
    }
  )
}


readFileEXEC2 <- function(path){
  createExecObj(function(cb){
    readFileCPS(path, cb)
  })
}


########### First iterations

createExecObj <- function(exec){
  list(
    exec = exec,
    bind = function(f){
      createExecObj(
        function(cb){
          exec(function(y){
            f(y)$exec(cb)
          })
        }
      )
    }
  )
}

callback_fun <- function(f){
  function(...){
    createExecObj(function(cb){
      cb(f(...))
    })  
  }
}

cbReadLines <- callback_fun(readLines)
cbReadLines("./file1")$bind(cbReadLines)$exec(print)



########### Second iterations

createExecObj <- function(exec){
  output <- list(
    exec = exec
  )
  class(output)<-"cb"
  output
}

compute.cb <- function(g, f){
  g$exec(f)
}


plot.cb <- function(g, f){
  createExecObj(
    function(cb){
      g$exec(function(y){
        f(y)$exec(cb)
      })
    }
  )  
}

callback_fun <- function(f){
  function(...){
    createExecObj(function(cb){
      cb(f(...))
    })  
  }
}

cbReadLines <- callback_fun(readLines)
cbReadLines("./file1") %>% plot(cbReadLines) %>% compute(print)



########### Third iterations

createExecObj <- function(exec){
  output <- list(
    exec = exec
  )
  class(output)<-"cb"
  output
}

compute.cb <- function(g, f){
  g$exec(f)
}

then.cb <- function(g, f){
  myf <- f
  if(!("cbfun" %in% class(f))){
    myf <- callback_fun(f)
  }
  createExecObj(
    function(cb){
      g$exec(function(y){
        myf(y)$exec(cb)
      })
    }
  )  
}

then <- function(x, ...){
  UseMethod("then", x)
}

callback_fun <- function(f){
  a <- function(...){
    createExecObj(function(cb){
      cb(f(...))
    })  
  }
  class(a) <- "cbfun"
  a
}

cbReadLines <- callback_fun(readLines)
cbReadLines("./file1") %>% then(cbReadLines) %>% compute(print)
cbReadLines("./file1") %>% then(readLines) %>% compute(print)