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Monads on R
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"%<-%" <- function(x,y) call("<-",substitute(x),substitute(y)) | |
returm <- function(x) call("return",substitute(x)) | |
exec <- quote | |
join <- function(ss,sep) { | |
res <- "" | |
for (s in ss) { | |
res <- paste(res,s,sep=sep) | |
} | |
res | |
} | |
monad <- function(bind, ret) { | |
list2call <- function(calls) { | |
t <- call("{") | |
for (x in calls) t[[length(t)+1]] <- x | |
return(t) | |
} | |
newfunc <- function(a,b) { | |
f <- eval(parse(text=paste("function(",a,"){}",sep=""))) | |
body(f) <- if (is.list(b)) list2call(b) else b | |
return(f) | |
} | |
function(...) { | |
ss <- list(...) | |
f <- (function(i,a,b) { | |
if (i>length(ss)) return(newfunc(a,b)) | |
s <- ss[[i]] | |
if (s[[1]] == "<-") { | |
r <- Recall(i+1,s[[2]],list()) | |
newfunc(a,append(b,call("bind",s[[3]],r))) | |
} else if (s[[1]] == "return") { | |
Recall(i+1,a,append(b,call("ret",s[[2]]))) | |
} | |
})(1,"",list()) | |
params <- append(as.list(parent.frame()),list(bind=bind,ret=ret)) | |
f <- evalq(eval(parse(text=join(deparse(f),""))),params) | |
f() | |
} | |
} | |
## Maybeモナド | |
maybe_do <- monad( | |
bind = function(x,f) if(is.na(x)) NA else f(x), | |
ret = function(x) x | |
) | |
maybe_test <- function() { | |
loves_list <- list( | |
c("Taro","Miki"), | |
c("Jiro","Hanako"), | |
c("Saburo","Hanako"), | |
c("Daisuke","Youko"), | |
c("Shunsuke","AnyGirl"), | |
c("Masatoshi","AnyGirl"), | |
c("Miki","Taro"), | |
c("Hanako","Daisuke"), | |
c("AnyGirl","Masao") | |
) | |
lover <- function(x) { | |
for (p in loves_list) { | |
if (x == p[1]) return(p[2]) | |
} | |
return(NA) | |
} | |
do <- maybe_do | |
couple_test <- function(a,b,lover) do ( | |
x %<-% lover(a), | |
y %<-% lover(x), | |
returm(x == b && y == a) | |
) | |
rival_test <- function(a,b,lover) do ( | |
x %<-% lover(a), | |
y %<-% lover(b), | |
returm(x == y) | |
) | |
jealousy_test <- function(a,b,lover) do ( | |
x %<-% lover(a), | |
y %<-% lover(x), | |
returm(y != a && y == b) | |
) | |
run <- function(test,a,b) { | |
print(paste(substitute(test),a,"-->",b,":",test(a,b,lover))) | |
} | |
run(couple_test,"Taro","Miki") | |
run(couple_test,"Jiro","Miki") | |
run(couple_test,"Daisuke","Youko") | |
run(rival_test,"Taro","Jiro") | |
run(rival_test,"Jiro","Saburo") | |
run(jealousy_test,"Shunsuke","Masao") | |
run(jealousy_test,"Shunsuke","Taro") | |
run(jealousy_test,"Jiro","Saburo") | |
} | |
maybe_test() |
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