This library provides facilities for parsing structured text data into concrete Elm values.
The Parser type.
At their core, Parsers wrap functions from some state and an
InputStream to a tuple representing the new state, the
remaining InputStream and a ParseResult res.
The input stream over which Parsers operate.
data is the initial input provided by the userinput is the remainder after running a parseposition is the starting position of input in data after a parseA record representing the current parse location in an InputStream.
source the current line of source codeline the current line number (starting at 1)column the current column (starting at 1)A tuple representing the current parser state, the remaining input
stream and the parse result. Don't worry about this type unless
you're writing your own primitive parsers.
Running a Parser results in one of two states:
Ok res when the parser has successfully parsed the inputErr messages when the parser has failed with a list of error messages.A tuple representing a failed parse. It contains the state after running the parser, the remaining input stream and a list of error messages.
A tuple representing a successful parse. It contains the state after running the parser, the remaining input stream and the result.
Parse a string. See runParser if your parser needs to manage
some internal state.
import Combine.Num exposing (int)
import String
parseAnInteger : String -> Result String Int
parseAnInteger input =
case parse int input of
Ok (_, stream, result) ->
Ok result
Err (_, stream, errors) ->
Err (String.join " or " errors)
parseAnInteger "123"
-- Ok 123
parseAnInteger "abc"
-- Err "expected an integer"
Parse a string while maintaining some internal state.
import Combine.Num exposing (int)
import String
type alias Output =
{ count : Int
, integers : List Int
}
statefulInt : Parse Int Int
statefulInt =
-- Parse an int, then increment the state and return the parsed
-- int. It's important that we try to parse the int _first_
-- since modifying the state will always succeed.
int <* modifyState ((+) 1)
ints : Parse Int (List Int)
ints =
sepBy (string " ") statefulInt
parseIntegers : String -> Result String Output
parseIntegers input =
case runParser ints 0 input of
Ok (state, stream, ints) ->
Ok { count = state, integers = ints }
Err (state, stream, errors) ->
Err (String.join " or " errors)
parseIntegers ""
-- Ok { count = 0, integers = [] }
parseIntegers "1 2 3 45"
-- Ok { count = 4, integers = [1, 2, 3, 45] }
parseIntegers "1 a 2"
-- Ok { count = 1, integers = [1] }
Construct a new primitive Parser.
If you find yourself reaching for this function often consider opening a Github issue with the library to have your custom Parsers included in the standard distribution.
Unwrap a parser so it can be applied to a state and an input
stream. This function is useful if you want to construct your own
parsers via primitive. If you're using this outside of the context
of primitive then you might be doing something wrong so try asking
for help on the mailing list.
Here's how you would implement a greedy version of manyTill using
primitive and app:
manyTill : Parser s a -> Parser s x -> Parser s (List a)
manyTill p end =
let
accumulate acc state stream =
case app end state stream of
( rstate, rstream, Ok _ ) ->
( rstate, rstream, Ok (List.reverse acc) )
_ ->
case app p state stream of
( rstate, rstream, Ok res ) ->
accumulate (res :: acc) rstate rstream
( estate, estream, Err ms ) ->
( estate, estream, Err ms )
in
primitive <| accumulate []
Defer running a parser until it's actually required. Use this function to avoid "bad-recursion" errors.
type Expression
= ETerm String
| EList (List E)
name : Parser s String
name = whitespace *> regex "[a-zA-Z]+" <* whitespace
term : Parser s Expression
term = ETerm <$> name
list : Parser s Expression
list =
let
-- helper is itself a function so we avoid the case where the
-- value `list` tries to apply itself in its definition.
helper () =
EList <$> between (string "(") (string ")") (many (term <|> list))
in
-- lazy defers calling helper until it's actually needed.
lazy helper
parse list ""
-- Err ["expected \"(\""]
parse list "()"
-- Ok (EList [])
parse list "(a (b c))"
-- Ok (EList [ETerm "a", EList [ETerm "b", ETerm "c"]])
Fail without consuming any input.
parse (fail "some error") "hello"
-- Err ["some error"]
Return a value without consuming any input.
parse (succeed 1) "a"
-- Ok 1
Parse an exact string match.
parse (string "hello") "hello world"
-- Ok "hello"
parse (string "hello") "goodbye"
-- Err ["expected \"hello\""]
Parse a Regex match.
Regular expressions must match from the beginning of the input and their
subgroups are ignored. A ^ is added implicitly to the beginning of
every pattern unless one already exists.
parse (regex "a+") "aaaaab"
-- Ok "aaaaa"
Fail when the input is not empty.
parse end ""
-- Ok ()
parse end "a"
-- Err ["expected end of input"]
Parse zero or more whitespace characters.
parse (whitespace *> string "hello") "hello"
-- Ok "hello"
parse (whitespace *> string "hello") " hello"
-- Ok "hello"
Parse one or more whitespace characters.
parse (whitespace1 *> string "hello") "hello"
-- Err ["whitespace"]
parse (whitespace1 *> string "hello") " hello"
-- Ok "hello"
Transform the result of a parser.
let
parser =
string "a"
|> map String.toUpper
in
parse parser "a"
-- Ok "A"
Transform the error of a parser.
let
parser =
string "a"
|> mapError (always ["bad input"])
in
parse parser b
-- Err ["bad input"]
)
Sequence two parsers, passing the result of the first parser to a function that returns the second parser. The value of the second parser is returned on success.
import Combine.Num exposing (int)
choosy : Parser s String
choosy =
let
createParser n =
if n % 2 == 0 then
string " is even"
else
string " is odd"
in
int
|> andThen createParser
parse choosy "1 is odd"
-- Ok " is odd"
parse choosy "2 is even"
-- Ok " is even"
parse choosy "1 is even"
-- Err ["expected \" is odd\""]
Sequence two parsers.
import Combine.Num exposing (int)
plus : Parser s String
plus = string "+"
sum : Parser s Int
sum =
int
|> map (+)
|> andMap (plus *> int)
parse sum "1+2"
-- Ok 3
), (*>), sequence
Apply a parser without consuming any input on success.
Consume input while the predicate matches.
parse (while ((/=) ' ')) "test 123"
-- Ok "test"
Choose between two parsers.
parse (or (string "a") (string "b")) "a"
-- Ok "a"
parse (or (string "a") (string "b")) "b"
-- Ok "b"
parse (or (string "a") (string "b")) "c"
-- Err ["expected \"a\"", "expected \"b\""]
Choose between a list of parsers.
parse (choice [string "a", string "b"]) "a"
-- Ok "a"
parse (choice [string "a", string "b"]) "b"
-- Ok "b"
Return a default value when the given parser fails.
letterA : Parser s String
letterA = optional "a" (string "a")
parse letterA "a"
-- Ok "a"
parse letterA "b"
-- Ok "a"
Wrap the return value into a Maybe. Returns Nothing on failure.
parse (maybe (string "a")) "a"
-- Ok (Just "a")
parse (maybe (string "a")) "b"
-- Ok Nothing
Apply a parser zero or more times and return a list of the results.
parse (many (string "a")) "aaab"
-- Ok ["a", "a", "a"]
parse (many (string "a")) "bbbb"
-- Ok []
parse (many (string "a")) ""
-- Ok []
Parse at least one result.
parse (many1 (string "a")) "a"
-- Ok ["a"]
parse (many1 (string "a")) ""
-- Err ["expected \"a\""]
Apply the first parser zero or more times until second parser succeeds. On success, the list of the first parser's results is returned.
string "<!--" *> manyTill anyChar (string "-->")
Parser zero or more occurences of one parser separated by another.
parse (sepBy (string ",") (string "a")) "b"
-- Ok []
parse (sepBy (string ",") (string "a")) "a,a,a"
-- Ok ["a", "a", "a"]
parse (sepBy (string ",") (string "a")) "a,a,b"
-- Ok ["a", "a"]
Parse one or more occurences of one parser separated by another.
Parse zero or more occurences of one parser separated and optionally ended by another.
parse (sepEndBy (string ",") (string "a")) "a,a,a,"
-- Ok ["a", "a", "a"]
Parse one or more occurences of one parser separated and optionally ended by another.
parse (sepEndBy1 (string ",") (string "a")) ""
-- Err ["expected \"a\""]
parse (sepEndBy1 (string ",") (string "a")) "a"
-- Ok ["a"]
parse (sepEndBy1 (string ",") (string "a")) "a,"
-- Ok ["a"]
Apply a parser and skip its result.
Apply a parser and skip its result many times.
Apply a parser and skip its result at least once.
Parse one or more occurences of p separated by op, recursively
apply all functions returned by op to the values returned by p. See
the examples/Calc.elm file for an example.
Similar to chainl but functions of op are applied in
right-associative order to the values of p. See the
examples/Python.elm file for a usage example.
Parse n occurences of p.
Parse something between two other parsers.
The parser
between (string "(") (string ")") (string "a")
is equivalent to the parser
string "(" *> string "a" <* string ")"
Parse something between parentheses.
Parse something between braces {}.
Parse something between square brackets [].
Get the parser's state and pipe it into a parser.
Replace the parser's state.
Modify the parser's state.
Get the current position in the input stream and pipe it into a parser.
Get the current line and pipe it into a parser.
Get the current column and pipe it into a parser.
Get the current (line, column) in the input stream.
Get the current source line in the input stream.
Get the current line in the input stream.
Get the current column in the input stream.
module Combine
exposing
( Parser
, InputStream
, ParseLocation
, ParseContext
, ParseResult
, ParseErr
, ParseOk
, primitive
, app
, lazy
, parse
, runParser
, withState
, putState
, modifyState
, withLocation
, withLine
, withColumn
, currentLocation
, currentSourceLine
, currentLine
, currentColumn
, map
, mapError
, andThen
, andMap
, sequence
, fail
, succeed
, string
, regex
, end
, whitespace
, whitespace1
, lookAhead
, while
, or
, choice
, optional
, maybe
, many
, many1
, manyTill
, sepBy
, sepBy1
, sepEndBy
, sepEndBy1
, skip
, skipMany
, skipMany1
, chainl
, chainr
, count
, between
, parens
, braces
, brackets
, (<?>)
, (>>=)
, (<$>)
, (<$)
, ($>)
, (<*>)
, (<*)
, (*>)
, (<|>)
)
{-| This library provides facilities for parsing structured text data
into concrete Elm values.
## API Reference
- [Core Types](#core-types)
- [Running Parsers](#running-parsers)
- [Constructing Parsers](#constructing-parsers)
- [Parsers](#parsers)
- [Combinators](#combinators)
- [Transforming Parsers](#transforming-parsers)
- [Chaining Parsers](#chaining-parsers)
- [Parser Combinators](#parser-combinators)
- [State Combinators](#state-combinators)
## Core Types
@docs Parser, InputStream, ParseLocation, ParseContext, ParseResult, ParseErr, ParseOk
## Running Parsers
@docs parse, runParser
## Constructing Parsers
@docs primitive, app, lazy
## Parsers
@docs fail, succeed, string, regex, end, whitespace, whitespace1
## Combinators
### Transforming Parsers
@docs map, (<$>), (<$), ($>), mapError, (<?>)
### Chaining Parsers
@docs andThen, (>>=), andMap, (<*>), (<*), (*>), sequence
### Parser Combinators
@docs lookAhead, while, or, (<|>), choice, optional, maybe, many, many1, manyTill, sepBy, sepBy1, sepEndBy, sepEndBy1, skip, skipMany, skipMany1, chainl, chainr, count, between, parens, braces, brackets
### State Combinators
@docs withState, putState, modifyState, withLocation, withLine, withColumn, currentLocation, currentSourceLine, currentLine, currentColumn
-}
import Lazy as L
import Regex exposing (Regex)
import String
{-| The input stream over which `Parser`s operate.
- `data` is the initial input provided by the user
- `input` is the remainder after running a parse
- `position` is the starting position of `input` in `data` after a parse
-}
type alias InputStream =
{ data : String
, input : String
, position : Int
}
initStream : String -> InputStream
initStream s =
InputStream s s 0
{-| A record representing the current parse location in an InputStream.
- `source` the current line of source code
- `line` the current line number (starting at 1)
- `column` the current column (starting at 1)
-}
type alias ParseLocation =
{ source : String
, line : Int
, column : Int
}
{-| A tuple representing the current parser state, the remaining input
stream and the parse result. Don't worry about this type unless
you're writing your own `primitive` parsers.
-}
type alias ParseContext state res =
( state, InputStream, ParseResult res )
{-| Running a `Parser` results in one of two states:
- `Ok res` when the parser has successfully parsed the input
- `Err messages` when the parser has failed with a list of error messages.
-}
type alias ParseResult res =
Result (List String) res
{-| A tuple representing a failed parse. It contains the state after
running the parser, the remaining input stream and a list of
error messages.
-}
type alias ParseErr state =
( state, InputStream, List String )
{-| A tuple representing a successful parse. It contains the state
after running the parser, the remaining input stream and the
result.
-}
type alias ParseOk state res =
( state, InputStream, res )
type alias ParseFn state res =
state -> InputStream -> ParseContext state res
{-| The Parser type.
At their core, `Parser`s wrap functions from some `state` and an
`InputStream` to a tuple representing the new `state`, the
remaining `InputStream` and a `ParseResult res`.
-}
type Parser state res
= Parser (ParseFn state res)
| RecursiveParser (L.Lazy (ParseFn state res))
{-| Construct a new primitive Parser.
If you find yourself reaching for this function often consider opening
a [Github issue][issues] with the library to have your custom Parsers
included in the standard distribution.
[issues]: https://github.com/elm-community/parser-combinators/issues
-}
primitive : (state -> InputStream -> ParseContext state res) -> Parser state res
primitive =
Parser
{-| Unwrap a parser so it can be applied to a state and an input
stream. This function is useful if you want to construct your own
parsers via `primitive`. If you're using this outside of the context
of `primitive` then you might be doing something wrong so try asking
for help on the mailing list.
Here's how you would implement a greedy version of `manyTill` using
`primitive` and `app`:
manyTill : Parser s a -> Parser s x -> Parser s (List a)
manyTill p end =
let
accumulate acc state stream =
case app end state stream of
( rstate, rstream, Ok _ ) ->
( rstate, rstream, Ok (List.reverse acc) )
_ ->
case app p state stream of
( rstate, rstream, Ok res ) ->
accumulate (res :: acc) rstate rstream
( estate, estream, Err ms ) ->
( estate, estream, Err ms )
in
primitive <| accumulate []
-}
app : Parser state res -> state -> InputStream -> ParseContext state res
app p =
case p of
Parser inner ->
inner
RecursiveParser t ->
L.force t
{-| Parse a string. See `runParser` if your parser needs to manage
some internal state.
import Combine.Num exposing (int)
import String
parseAnInteger : String -> Result String Int
parseAnInteger input =
case parse int input of
Ok (_, stream, result) ->
Ok result
Err (_, stream, errors) ->
Err (String.join " or " errors)
parseAnInteger "123"
-- Ok 123
parseAnInteger "abc"
-- Err "expected an integer"
-}
parse : Parser () res -> String -> Result (ParseErr ()) (ParseOk () res)
parse p =
runParser p ()
{-| Parse a string while maintaining some internal state.
import Combine.Num exposing (int)
import String
type alias Output =
{ count : Int
, integers : List Int
}
statefulInt : Parse Int Int
statefulInt =
-- Parse an int, then increment the state and return the parsed
-- int. It's important that we try to parse the int _first_
-- since modifying the state will always succeed.
int <* modifyState ((+) 1)
ints : Parse Int (List Int)
ints =
sepBy (string " ") statefulInt
parseIntegers : String -> Result String Output
parseIntegers input =
case runParser ints 0 input of
Ok (state, stream, ints) ->
Ok { count = state, integers = ints }
Err (state, stream, errors) ->
Err (String.join " or " errors)
parseIntegers ""
-- Ok { count = 0, integers = [] }
parseIntegers "1 2 3 45"
-- Ok { count = 4, integers = [1, 2, 3, 45] }
parseIntegers "1 a 2"
-- Ok { count = 1, integers = [1] }
-}
runParser : Parser state res -> state -> String -> Result (ParseErr state) (ParseOk state res)
runParser p st s =
case app p st (initStream s) of
( state, stream, Ok res ) ->
Ok ( state, stream, res )
( state, stream, Err ms ) ->
Err ( state, stream, ms )
{-| Defer running a parser until it's actually required. Use this
function to avoid "bad-recursion" errors.
type Expression
= ETerm String
| EList (List E)
name : Parser s String
name = whitespace *> regex "[a-zA-Z]+" <* whitespace
term : Parser s Expression
term = ETerm <$> name
list : Parser s Expression
list =
let
-- helper is itself a function so we avoid the case where the
-- value `list` tries to apply itself in its definition.
helper () =
EList <$> between (string "(") (string ")") (many (term <|> list))
in
-- lazy defers calling helper until it's actually needed.
lazy helper
parse list ""
-- Err ["expected \"(\""]
parse list "()"
-- Ok (EList [])
parse list "(a (b c))"
-- Ok (EList [ETerm "a", EList [ETerm "b", ETerm "c"]])
-}
lazy : (() -> Parser s a) -> Parser s a
lazy t =
RecursiveParser (L.lazy (\() -> app (t ())))
{-| Transform both the result and error message of a parser.
-}
bimap :
(a -> b)
-> (List String -> List String)
-> Parser s a
-> Parser s b
bimap fok ferr p =
Parser <|
\state stream ->
case app p state stream of
( rstate, rstream, Ok res ) ->
( rstate, rstream, Ok (fok res) )
( estate, estream, Err ms ) ->
( estate, estream, Err (ferr ms) )
-- State management
-- ----------------
{-| Get the parser's state and pipe it into a parser.
-}
withState : (s -> Parser s a) -> Parser s a
withState f =
Parser <|
\state stream ->
app (f state) state stream
{-| Replace the parser's state.
-}
putState : s -> Parser s ()
putState state =
Parser <|
\_ stream ->
app (succeed ()) state stream
{-| Modify the parser's state.
-}
modifyState : (s -> s) -> Parser s ()
modifyState f =
Parser <|
\state stream ->
app (succeed ()) (f state) stream
{-| Get the current position in the input stream and pipe it into a parser.
-}
withLocation : (ParseLocation -> Parser s a) -> Parser s a
withLocation f =
Parser <|
\state stream ->
app (f <| currentLocation stream) state stream
{-| Get the current line and pipe it into a parser.
-}
withLine : (Int -> Parser s a) -> Parser s a
withLine f =
Parser <|
\state stream ->
app (f <| currentLine stream) state stream
{-| Get the current column and pipe it into a parser.
-}
withColumn : (Int -> Parser s a) -> Parser s a
withColumn f =
Parser <|
\state stream ->
app (f <| currentColumn stream) state stream
{-| Get the current `(line, column)` in the input stream.
-}
currentLocation : InputStream -> ParseLocation
currentLocation stream =
let
find position currentLine lines =
case lines of
[] ->
ParseLocation "" currentLine position
line :: rest ->
let
length =
String.length line
lengthPlusNL =
length + 1
in
if position == length then
ParseLocation line currentLine position
else if position > length then
find (position - lengthPlusNL) (currentLine + 1) rest
else
ParseLocation line currentLine position
in
find stream.position 0 (String.split "\n" stream.data)
{-| Get the current source line in the input stream.
-}
currentSourceLine : InputStream -> String
currentSourceLine =
currentLocation >> .source
{-| Get the current line in the input stream.
-}
currentLine : InputStream -> Int
currentLine =
currentLocation >> .line
{-| Get the current column in the input stream.
-}
currentColumn : InputStream -> Int
currentColumn =
currentLocation >> .column
-- Transformers
-- ------------
{-| Transform the result of a parser.
let
parser =
string "a"
|> map String.toUpper
in
parse parser "a"
-- Ok "A"
-}
map : (a -> b) -> Parser s a -> Parser s b
map f p =
bimap f identity p
{-| Transform the error of a parser.
let
parser =
string "a"
|> mapError (always ["bad input"])
in
parse parser b
-- Err ["bad input"]
-}
mapError : (List String -> List String) -> Parser s a -> Parser s a
mapError =
bimap identity
{-| Sequence two parsers, passing the result of the first parser to a
function that returns the second parser. The value of the second
parser is returned on success.
import Combine.Num exposing (int)
choosy : Parser s String
choosy =
let
createParser n =
if n % 2 == 0 then
string " is even"
else
string " is odd"
in
int
|> andThen createParser
parse choosy "1 is odd"
-- Ok " is odd"
parse choosy "2 is even"
-- Ok " is even"
parse choosy "1 is even"
-- Err ["expected \" is odd\""]
-}
andThen : (a -> Parser s b) -> Parser s a -> Parser s b
andThen f p =
Parser <|
\state stream ->
case app p state stream of
( rstate, rstream, Ok res ) ->
app (f res) rstate rstream
( estate, estream, Err ms ) ->
( estate, estream, Err ms )
{-| Sequence two parsers.
import Combine.Num exposing (int)
plus : Parser s String
plus = string "+"
sum : Parser s Int
sum =
int
|> map (+)
|> andMap (plus *> int)
parse sum "1+2"
-- Ok 3
-}
andMap : Parser s a -> Parser s (a -> b) -> Parser s b
andMap rp lp =
lp >>= flip map rp
{-| Run a list of parsers in sequence, accumulating the results. The
main use case for this parser is when you want to combine a list of
parsers into a single, top-level, parser. For most use cases, you'll
want to use one of the other combinators instead.
parse (sequence [string "a", string "b"]) "ab"
-- Ok ["a", "b"]
parse (sequence [string "a", string "b"]) "ac"
-- Err ["expected \"b\""]
-}
sequence : List (Parser s a) -> Parser s (List a)
sequence parsers =
let
accumulate acc ps state stream =
case ps of
[] ->
( state, stream, Ok (List.reverse acc) )
x :: xs ->
case app x state stream of
( rstate, rstream, Ok res ) ->
accumulate (res :: acc) xs rstate rstream
( estate, estream, Err ms ) ->
( estate, estream, Err ms )
in
Parser <|
\state stream ->
accumulate [] parsers state stream
-- Combinators
-- -----------
{-| Fail without consuming any input.
parse (fail "some error") "hello"
-- Err ["some error"]
-}
fail : String -> Parser s a
fail m =
Parser <|
\state stream ->
( state, stream, Err [ m ] )
emptyErr : Parser s a
emptyErr =
Parser <|
\state stream ->
( state, stream, Err [] )
{-| Return a value without consuming any input.
parse (succeed 1) "a"
-- Ok 1
-}
succeed : a -> Parser s a
succeed res =
Parser <|
\state stream ->
( state, stream, Ok res )
{-| Parse an exact string match.
parse (string "hello") "hello world"
-- Ok "hello"
parse (string "hello") "goodbye"
-- Err ["expected \"hello\""]
-}
string : String -> Parser s String
string s =
Parser <|
\state stream ->
if String.startsWith s stream.input then
let
len =
String.length s
rem =
String.dropLeft len stream.input
pos =
stream.position + len
in
( state, { stream | input = rem, position = pos }, Ok s )
else
( state, stream, Err [ "expected " ++ toString s ] )
{-| Parse a Regex match.
Regular expressions must match from the beginning of the input and their
subgroups are ignored. A `^` is added implicitly to the beginning of
every pattern unless one already exists.
parse (regex "a+") "aaaaab"
-- Ok "aaaaa"
-}
regex : String -> Parser s String
regex pat =
let
pattern =
if String.startsWith "^" pat then
pat
else
"^" ++ pat
in
Parser <|
\state stream ->
case Regex.find (Regex.AtMost 1) (Regex.regex pattern) stream.input of
[ match ] ->
let
len =
String.length match.match
rem =
String.dropLeft len stream.input
pos =
stream.position + len
in
( state, { stream | input = rem, position = pos }, Ok match.match )
_ ->
( state, stream, Err [ "expected input matching Regexp /" ++ pattern ++ "/" ] )
{-| Consume input while the predicate matches.
parse (while ((/=) ' ')) "test 123"
-- Ok "test"
-}
while : (Char -> Bool) -> Parser s String
while pred =
let
accumulate acc state stream =
case String.uncons stream.input of
Just ( h, rest ) ->
if pred h then
let
c =
String.cons h ""
pos =
stream.position + 1
in
accumulate (acc ++ c) state { stream | input = rest, position = pos }
else
( state, stream, acc )
Nothing ->
( state, stream, acc )
in
Parser <|
\state stream ->
let
( rstate, rstream, res ) =
accumulate "" state stream
in
( rstate, rstream, Ok res )
{-| Fail when the input is not empty.
parse end ""
-- Ok ()
parse end "a"
-- Err ["expected end of input"]
-}
end : Parser s ()
end =
Parser <|
\state stream ->
if stream.input == "" then
( state, stream, Ok () )
else
( state, stream, Err [ "expected end of input" ] )
{-| Apply a parser without consuming any input on success.
-}
lookAhead : Parser s a -> Parser s a
lookAhead p =
Parser <|
\state stream ->
case app p state stream of
( rstate, _, Ok res ) ->
( rstate, stream, Ok res )
err ->
err
{-| Choose between two parsers.
parse (or (string "a") (string "b")) "a"
-- Ok "a"
parse (or (string "a") (string "b")) "b"
-- Ok "b"
parse (or (string "a") (string "b")) "c"
-- Err ["expected \"a\"", "expected \"b\""]
-}
or : Parser s a -> Parser s a -> Parser s a
or lp rp =
Parser <|
\state stream ->
case app lp state stream of
( _, _, Ok _ ) as res ->
res
( _, _, Err lms ) ->
case app rp state stream of
( _, _, Ok _ ) as res ->
res
( _, _, Err rms ) ->
( state, stream, Err (lms ++ rms) )
{-| Choose between a list of parsers.
parse (choice [string "a", string "b"]) "a"
-- Ok "a"
parse (choice [string "a", string "b"]) "b"
-- Ok "b"
-}
choice : List (Parser s a) -> Parser s a
choice xs =
List.foldr or emptyErr xs
{-| Return a default value when the given parser fails.
letterA : Parser s String
letterA = optional "a" (string "a")
parse letterA "a"
-- Ok "a"
parse letterA "b"
-- Ok "a"
-}
optional : a -> Parser s a -> Parser s a
optional res p =
p <|> succeed res
{-| Wrap the return value into a `Maybe`. Returns `Nothing` on failure.
parse (maybe (string "a")) "a"
-- Ok (Just "a")
parse (maybe (string "a")) "b"
-- Ok Nothing
-}
maybe : Parser s a -> Parser s (Maybe a)
maybe p =
Parser <|
\state stream ->
case app p state stream of
( rstate, rstream, Ok res ) ->
( rstate, rstream, Ok (Just res) )
_ ->
( state, stream, Ok Nothing )
{-| Apply a parser zero or more times and return a list of the results.
parse (many (string "a")) "aaab"
-- Ok ["a", "a", "a"]
parse (many (string "a")) "bbbb"
-- Ok []
parse (many (string "a")) ""
-- Ok []
-}
many : Parser s a -> Parser s (List a)
many p =
let
accumulate acc state stream =
case app p state stream of
( rstate, rstream, Ok res ) ->
if stream == rstream then
( rstate, rstream, List.reverse acc )
else
accumulate (res :: acc) rstate rstream
_ ->
( state, stream, List.reverse acc )
in
Parser <|
\state stream ->
let
( rstate, rstream, res ) =
accumulate [] state stream
in
( rstate, rstream, Ok res )
{-| Parse at least one result.
parse (many1 (string "a")) "a"
-- Ok ["a"]
parse (many1 (string "a")) ""
-- Err ["expected \"a\""]
-}
many1 : Parser s a -> Parser s (List a)
many1 p =
(::) <$> p <*> many p
{-| Apply the first parser zero or more times until second parser
succeeds. On success, the list of the first parser's results is returned.
string "<!--" *> manyTill anyChar (string "-->")
-}
manyTill : Parser s a -> Parser s end -> Parser s (List a)
manyTill p end =
let
accumulate acc state stream =
case app end state stream of
( rstate, rstream, Ok _ ) ->
( rstate, rstream, Ok (List.reverse acc) )
( estate, estream, Err ms ) ->
case app p state stream of
( rstate, rstream, Ok res ) ->
accumulate (res :: acc) rstate rstream
_ ->
( estate, estream, Err ms )
in
Parser (accumulate [])
{-| Parser zero or more occurences of one parser separated by another.
parse (sepBy (string ",") (string "a")) "b"
-- Ok []
parse (sepBy (string ",") (string "a")) "a,a,a"
-- Ok ["a", "a", "a"]
parse (sepBy (string ",") (string "a")) "a,a,b"
-- Ok ["a", "a"]
-}
sepBy : Parser s x -> Parser s a -> Parser s (List a)
sepBy sep p =
sepBy1 sep p <|> succeed []
{-| Parse one or more occurences of one parser separated by another.
-}
sepBy1 : Parser s x -> Parser s a -> Parser s (List a)
sepBy1 sep p =
(::) <$> p <*> many (sep *> p)
{-| Parse zero or more occurences of one parser separated and
optionally ended by another.
parse (sepEndBy (string ",") (string "a")) "a,a,a,"
-- Ok ["a", "a", "a"]
-}
sepEndBy : Parser s x -> Parser s a -> Parser s (List a)
sepEndBy sep p =
sepEndBy1 sep p <|> succeed []
{-| Parse one or more occurences of one parser separated and
optionally ended by another.
parse (sepEndBy1 (string ",") (string "a")) ""
-- Err ["expected \"a\""]
parse (sepEndBy1 (string ",") (string "a")) "a"
-- Ok ["a"]
parse (sepEndBy1 (string ",") (string "a")) "a,"
-- Ok ["a"]
-}
sepEndBy1 : Parser s x -> Parser s a -> Parser s (List a)
sepEndBy1 sep p =
sepBy1 sep p <* maybe sep
{-| Apply a parser and skip its result.
-}
skip : Parser s x -> Parser s ()
skip p =
() <$ p
{-| Apply a parser and skip its result many times.
-}
skipMany : Parser s x -> Parser s ()
skipMany p =
() <$ many (skip p)
{-| Apply a parser and skip its result at least once.
-}
skipMany1 : Parser s x -> Parser s ()
skipMany1 p =
() <$ many1 (skip p)
{-| Parse one or more occurences of `p` separated by `op`, recursively
apply all functions returned by `op` to the values returned by `p`. See
the `examples/Calc.elm` file for an example.
-}
chainl : Parser s (a -> a -> a) -> Parser s a -> Parser s a
chainl op p =
let
accumulate x =
(op
|> andThen
(\f ->
p
|> andThen (\y -> accumulate (f x y))
)
)
<|> succeed x
in
andThen accumulate p
{-| Similar to `chainl` but functions of `op` are applied in
right-associative order to the values of `p`. See the
`examples/Python.elm` file for a usage example.
-}
chainr : Parser s (a -> a -> a) -> Parser s a -> Parser s a
chainr op p =
let
accumulate x =
(op
|> andThen
(\f ->
p
|> andThen accumulate
|> andThen (\y -> succeed (f x y))
)
)
<|> succeed x
in
andThen accumulate p
{-| Parse `n` occurences of `p`.
-}
count : Int -> Parser s a -> Parser s (List a)
count n p =
let
accumulate x acc =
if x <= 0 then
succeed (List.reverse acc)
else
andThen (\res -> accumulate (x - 1) (res :: acc)) p
in
accumulate n []
{-| Parse something between two other parsers.
The parser
between (string "(") (string ")") (string "a")
is equivalent to the parser
string "(" *> string "a" <* string ")"
-}
between : Parser s l -> Parser s r -> Parser s a -> Parser s a
between lp rp p =
lp *> p <* rp
{-| Parse something between parentheses.
-}
parens : Parser s a -> Parser s a
parens =
between (string "(") (string ")")
{-| Parse something between braces `{}`.
-}
braces : Parser s a -> Parser s a
braces =
between (string "{") (string "}")
{-| Parse something between square brackets `[]`.
-}
brackets : Parser s a -> Parser s a
brackets =
between (string "[") (string "]")
{-| Parse zero or more whitespace characters.
parse (whitespace *> string "hello") "hello"
-- Ok "hello"
parse (whitespace *> string "hello") " hello"
-- Ok "hello"
-}
whitespace : Parser s String
whitespace =
regex "[ \t\x0D\n]*" <?> "whitespace"
{-| Parse one or more whitespace characters.
parse (whitespace1 *> string "hello") "hello"
-- Err ["whitespace"]
parse (whitespace1 *> string "hello") " hello"
-- Ok "hello"
-}
whitespace1 : Parser s String
whitespace1 =
regex "[ \t\x0D\n]+" <?> "whitespace"
-- Infix operators
-- ---------------
{-| Variant of `mapError` that replaces the Parser's error with a List
of a single string.
parse (string "a" <?> "gimme an 'a'") "b"
-- Err ["gimme an 'a'"]
-}
(<?>) : Parser s a -> String -> Parser s a
(<?>) p m =
mapError (always [ m ]) p
{-| Infix version of `andThen`.
import Combine.Num exposing (int)
choosy : Parser s String
choosy =
let
createParser n =
if n % 2 == 0 then
string " is even"
else
string " is odd"
in
int >>= createParser
parse choosy "1 is odd"
-- Ok " is odd"
parse choosy "2 is even"
-- Ok " is even"
parse choosy "1 is even"
-- Err ["expected \" is odd\""]
-}
(>>=) : Parser s a -> (a -> Parser s b) -> Parser s b
(>>=) =
flip andThen
{-| Infix version of `map`.
parse (toString <$> int) "42"
-- Ok "42"
parse (toString <$> int) "abc"
-- Err ["expected an integer"]
-}
(<$>) : (a -> b) -> Parser s a -> Parser s b
(<$>) =
map
{-| Run a parser and return the value on the left on success.
parse (True <$ string "true") "true"
-- Ok True
parse (True <$ string "true") "false"
-- Err ["expected \"true\""]
-}
(<$) : a -> Parser s x -> Parser s a
(<$) res =
map (always res)
{-| Run a parser and return the value on the right on success.
parse (string "true" $> True) "true"
-- Ok True
parse (string "true" $> True) "false"
-- Err ["expected \"true\""]
-}
($>) : Parser s x -> a -> Parser s a
($>) =
flip (<$)
{-| Infix version of `andMap`.
add : Int -> Int -> Int
add = (+)
plus : Parser s String
plus = string "+"
parse (add <$> int <*> (plus *> int)) "1+1"
-- Ok 2
-}
(<*>) : Parser s (a -> b) -> Parser s a -> Parser s b
(<*>) =
flip andMap
{-| Join two parsers, ignoring the result of the one on the right.
unsuffix : Parser s String
unsuffix =
regex "[a-z]"
<* regex "[!?]"
parse unsuffix "a!"
-- Ok "a"
-}
(<*) : Parser s a -> Parser s x -> Parser s a
(<*) lp rp =
lp
|> map always
|> andMap rp
{-| Join two parsers, ignoring the result of the one on the left.
unprefix : Parser s String
unprefix =
string ">"
*> while ((==) ' ')
*> while ((/=) ' ')
parse unprefix "> a"
-- Ok "a"
-}
(*>) : Parser s x -> Parser s a -> Parser s a
(*>) lp rp =
lp
|> map (flip always)
|> andMap rp
{-| Synonym for `or`.
-}
(<|>) : Parser s a -> Parser s a -> Parser s a
(<|>) =
or
-- Fixities
infixl 1 >>=
infixr 1 <|>
infixl 4 <$>
infixl 4 <$
infixl 4 $>
infixl 4 <*>
infixl 4 <*
infixl 4 *>