Evaluate a list of computation expression values
up vote
2
down vote
favorite
What's a good way to evaluate a list of computation expression values into the corresponding list of values?
Let's say my computation expression type is M<a> then I'm wondering what is the best way to write the function:
mysequence : list<M<'a>> -> M<list<'a>>
I could write this out recursively:
let rec mysequence = function
| -> builder { return }
| (x::xs) -> builder { let! y = x
let! ys = mysequence xs
return (y::ys)
}
Is there a more concise way?
f#
asked Nov 12 at 4:24
Strecster
352
add a comment |
up vote
2
down vote
favorite
What's a good way to evaluate a list of computation expression values into the corresponding list of values?
Let's say my computation expression type is M<a> then I'm wondering what is the best way to write the function:
mysequence : list<M<'a>> -> M<list<'a>>
I could write this out recursively:
let rec mysequence = function
| -> builder { return }
| (x::xs) -> builder { let! y = x
let! ys = mysequence xs
return (y::ys)
}
Is there a more concise way?
f#
asked Nov 12 at 4:24
Strecster
352
add a comment |
up vote
2
down vote
favorite
up vote
2
down vote
favorite
What's a good way to evaluate a list of computation expression values into the corresponding list of values?
Let's say my computation expression type is M<a> then I'm wondering what is the best way to write the function:
mysequence : list<M<'a>> -> M<list<'a>>
I could write this out recursively:
let rec mysequence = function
| -> builder { return }
| (x::xs) -> builder { let! y = x
let! ys = mysequence xs
return (y::ys)
}
Is there a more concise way?
f#
asked Nov 12 at 4:24
Strecster
352
What's a good way to evaluate a list of computation expression values into the corresponding list of values?
Let's say my computation expression type is M<a> then I'm wondering what is the best way to write the function:
mysequence : list<M<'a>> -> M<list<'a>>
I could write this out recursively:
let rec mysequence = function
| -> builder { return }
| (x::xs) -> builder { let! y = x
let! ys = mysequence xs
return (y::ys)
}
Is there a more concise way?
f#
f#
asked Nov 12 at 4:24
Strecster
352
asked Nov 12 at 4:24
Strecster
352
asked Nov 12 at 4:24
Strecster
352
asked Nov 12 at 4:24
Strecster
352
asked Nov 12 at 4:24
Strecster
352
352
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
up vote
4
down vote
accepted
You could make this a bit shorter by using List.fold and even shorter if you introduced a couple of helper combinators such as a lift2 function of the following type:
lift2 : ('a -> 'b -> 'c) -> M<'a> -> M<'b> -> M<'c>
This is something you can easily define using the builder { .. } notation and it lets you turn functions that work on normal values into functions that work on wrapped values. You could then lift the list consing operation and use that with fold. Doing that will make the code shorter (if you ignore all the helpers one has to write), but it also makes it pretty ugly and obscure.
If I was writing this, I'd go with something very close to your version. I prefer to keep the entire body in builder { .. } rather than having function and I'd also use the accumulator parameter, so I'd write:
let rec mysequence acc input = builder {
match input with
| -> return List.rev acc
| x::xs ->
let! y = x
return! mysequence (y::acc) xs }
But aside from the accumulator and some minor syntactic differences, it's pretty much the same as yours!
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
You could make this a bit shorter by using List.fold and even shorter if you introduced a couple of helper combinators such as a lift2 function of the following type:
lift2 : ('a -> 'b -> 'c) -> M<'a> -> M<'b> -> M<'c>
This is something you can easily define using the builder { .. } notation and it lets you turn functions that work on normal values into functions that work on wrapped values. You could then lift the list consing operation and use that with fold. Doing that will make the code shorter (if you ignore all the helpers one has to write), but it also makes it pretty ugly and obscure.
If I was writing this, I'd go with something very close to your version. I prefer to keep the entire body in builder { .. } rather than having function and I'd also use the accumulator parameter, so I'd write:
let rec mysequence acc input = builder {
match input with
| -> return List.rev acc
| x::xs ->
let! y = x
return! mysequence (y::acc) xs }
But aside from the accumulator and some minor syntactic differences, it's pretty much the same as yours!
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
add a comment |
up vote
4
down vote
accepted
You could make this a bit shorter by using List.fold and even shorter if you introduced a couple of helper combinators such as a lift2 function of the following type:
lift2 : ('a -> 'b -> 'c) -> M<'a> -> M<'b> -> M<'c>
This is something you can easily define using the builder { .. } notation and it lets you turn functions that work on normal values into functions that work on wrapped values. You could then lift the list consing operation and use that with fold. Doing that will make the code shorter (if you ignore all the helpers one has to write), but it also makes it pretty ugly and obscure.
If I was writing this, I'd go with something very close to your version. I prefer to keep the entire body in builder { .. } rather than having function and I'd also use the accumulator parameter, so I'd write:
let rec mysequence acc input = builder {
match input with
| -> return List.rev acc
| x::xs ->
let! y = x
return! mysequence (y::acc) xs }
But aside from the accumulator and some minor syntactic differences, it's pretty much the same as yours!
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
add a comment |
up vote
4
down vote
accepted
up vote
4
down vote
accepted
You could make this a bit shorter by using List.fold and even shorter if you introduced a couple of helper combinators such as a lift2 function of the following type:
lift2 : ('a -> 'b -> 'c) -> M<'a> -> M<'b> -> M<'c>
This is something you can easily define using the builder { .. } notation and it lets you turn functions that work on normal values into functions that work on wrapped values. You could then lift the list consing operation and use that with fold. Doing that will make the code shorter (if you ignore all the helpers one has to write), but it also makes it pretty ugly and obscure.
If I was writing this, I'd go with something very close to your version. I prefer to keep the entire body in builder { .. } rather than having function and I'd also use the accumulator parameter, so I'd write:
let rec mysequence acc input = builder {
match input with
| -> return List.rev acc
| x::xs ->
let! y = x
return! mysequence (y::acc) xs }
But aside from the accumulator and some minor syntactic differences, it's pretty much the same as yours!
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
You could make this a bit shorter by using List.fold and even shorter if you introduced a couple of helper combinators such as a lift2 function of the following type:
lift2 : ('a -> 'b -> 'c) -> M<'a> -> M<'b> -> M<'c>
This is something you can easily define using the builder { .. } notation and it lets you turn functions that work on normal values into functions that work on wrapped values. You could then lift the list consing operation and use that with fold. Doing that will make the code shorter (if you ignore all the helpers one has to write), but it also makes it pretty ugly and obscure.
If I was writing this, I'd go with something very close to your version. I prefer to keep the entire body in builder { .. } rather than having function and I'd also use the accumulator parameter, so I'd write:
let rec mysequence acc input = builder {
match input with
| -> return List.rev acc
| x::xs ->
let! y = x
return! mysequence (y::acc) xs }
But aside from the accumulator and some minor syntactic differences, it's pretty much the same as yours!
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
answered Nov 12 at 11:50
Tomas Petricek
197k13285459
197k13285459
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
add a comment |
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
Thankyou Tomas, very informative.
– Strecster
Nov 12 at 22:32
add a comment |
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