diff options
| -rw-r--r-- | src/parcom.cr | 15 | ||||
| -rw-r--r-- | src/parcom/alt.cr | 28 |
2 files changed, 28 insertions, 15 deletions
diff --git a/src/parcom.cr b/src/parcom.cr index 82c4c3b..44a770c 100644 --- a/src/parcom.cr +++ b/src/parcom.cr @@ -81,21 +81,6 @@ module Parcom end end - class Alt(T, V) < Parser(T, V) - def initialize(@p1 : Parser(T, V), @p2 : Parser(T, V)) - end - - def parse(tokens : Tokens(T)) : Result(T, V) - @p1.parse(tokens) - rescue ex1 : ParserFail - begin - @p2.parse(tokens) - rescue ex2 : ParserFail - raise ParserFail.new("Alt (#{ex1.message}), (#{ex2.message})") - end - end - end - class Map(T, V, U) < Parser(T, U) def initialize(@p : Parser(T, V), &block : V -> U) @f = block diff --git a/src/parcom/alt.cr b/src/parcom/alt.cr new file mode 100644 index 0000000..dedd41d --- /dev/null +++ b/src/parcom/alt.cr @@ -0,0 +1,28 @@ +require "./parser.cr" + +module Parcom + # `Alt` is a `Parser` that accepts two other parsers and tries + # to parse with one of them. + # If the first (left) parser succeeds, its result is returned. + # If the first parser fails, it will try the second (right) parser. + class Alt(T, V) < Parser(T, V) + # Accepts the two parsers to try to parse with. + def initialize(@p1 : Parser(T, V), @p2 : Parser(T, V)) + end + + # Tries to parse using both parsers. + # + # It will initially try to parse with the first parser. + # If it fails, it will try to parse with the second parser. + def parse(tokens : Tokens(T)) : Result(T, V) + @p1.parse(tokens) + rescue ex1 : ParserFail + begin + @p2.parse(tokens) + rescue ex2 : ParserFail + raise ParserFail.new("Alt (#{ex1.message}), (#{ex2.message})") + end + end + end +end + |