Rmonad: cheatsheet

Zebulun Arendsee

This work is funded by the National Science Foundation grant NSF-IOS 1546858.

Here are the currently supported operators:

%>>% - pass left hand side (lhs) as initial argument of right hand side (rhs) function
%v>% - like %>>% but stores lhs value
%>_% - like %>>% but passes lhs instead of rhs – propagates rhs failure
%>^% - like %>_% but does not propagate rhs failure, branch operator
%||% - use rhs value if lhs is failing
%|>% - call rhs on lhs if lhs failed
%*>% - treat lhs as list of arguments passed to the rhs function
%__% - ignore lhs, rhs starts a new chain (but preserves lhs history)

The design space can be enumerated with following states:

lhs class
1. a value
2. a list of values
rhs class
1. function of lhs
2. a value independent of the lhs
Value is stored
1. no
2. yes
What is passed
1. the output of the rhs
2. the output of the lhs
3. the value of the rhs if the lhs failed
Operations passes if
1. lhs and rhs both pass
2. lhs or rhs pass
3. lhs passes
4. rhs passes

Given these states, the current operators can be represented as

%>>% - 00000
%*>% - 10000
%v>% - 00100
%>_% - 00010
%>^% - 00012
%__% - 01003
%||% - 01021
%|>% - 00021

There are a lot of potentially useful combinations that are not used. And there are likely other operator types not in this space that would be useful.

Below is reformating of the same information:

op	lhs	rhs	store	passes	runif	pass error
`%>>%`	x	f(x)	-	f(x)	x passes	yes
`%v>%`	x	f(x)	x	f(x)	x passes	yes
`%>_%`	x	f(x)	-	x	x passes	yes
`%>^%`	x	f(x)	-	x	x passes	no
`%\|>%`	x	f(x)	-	x or f(x)	x fails	no
`%\|\|%`	x	y	-	x or y	x fails	no
`%*>%`	…	f(…)	-	f(…)	all … pass	yes
`%__%`	x	y	-	y	always	no

The operator %^>%, used for branch merging, is on the chop block. It can be replaced with a combination of funnel and %*>%. The operator is too specialized and convoluted.

Helper functions

esc - extract current value and raise any exceptions
mtabulate - summarize the pipeline in tabular form
missues - list all warnings and errors
funnel - merge pipelines

Examples

library(rmonad)

letters[1:5] %>>% paste(collapse="")
letters[1:5] %v>% paste(collapse="")
rnorm(1) %>_%
  { stopifnot(. > 0 & . < 1) } %>>%
  { rbinom(n=10, size=5, prob=.) } 

rnorm(1) %>^%
  {

      "This is a seperate branch, it fails if '.' is not between 0 and 1"

      . %>_%
        { stopifnot(. > 0 & . < 1) } %>>%
        { rbinom(n=10, size=5, prob=.) }
  } %>>%
  {

      "This will run even if the branch producing the binomial random
      variables fails. It never fails."

      rnorm(n=10, mean=.,sd=1)
  }