From b274828831fec26cd8b3089ffef14cb96ce2de2f Mon Sep 17 00:00:00 2001 From: Matthew Hall Date: Thu, 16 Mar 2023 20:36:03 +1300 Subject: Second rewrite attempt, this one should work, monkaS --- src/__OLD_parcom/alt.cr | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) create mode 100644 src/__OLD_parcom/alt.cr (limited to 'src/__OLD_parcom/alt.cr') diff --git a/src/__OLD_parcom/alt.cr b/src/__OLD_parcom/alt.cr new file mode 100644 index 0000000..dedd41d --- /dev/null +++ b/src/__OLD_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 + -- cgit v1.2.1