From b274828831fec26cd8b3089ffef14cb96ce2de2f Mon Sep 17 00:00:00 2001
From: Matthew Hall <hallmatthew314@gmail.com>
Date: Thu, 16 Mar 2023 20:36:03 +1300
Subject: Second rewrite attempt, this one should work, monkaS

---
 src/__OLD_parcom/parser.cr | 87 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 src/__OLD_parcom/parser.cr

(limited to 'src/__OLD_parcom/parser.cr')

diff --git a/src/__OLD_parcom/parser.cr b/src/__OLD_parcom/parser.cr
new file mode 100644
index 0000000..ca350df
--- /dev/null
+++ b/src/__OLD_parcom/parser.cr
@@ -0,0 +1,87 @@
+require "../parcom.cr"
+
+module Parcom
+  # `Parser` is the base class of all parser objects and contains
+  # a handful of helper methods that can allow for cleaner syntax.
+  #
+  # The generic type `T` represents the type of tokens a parser will
+  # operate on (usually `Char`).
+  # The generic type `V` represents the type of value that a parser
+  # will return when parsing is successful.
+  abstract class Parser(T, V)
+    # Accepts a `Tokens(T)` and either retuns a `Result(T, V)`, or raises a
+    # `ParserFail` exception with a message providing context of where
+    # in the chain the parsing failed.
+    #
+    # The `V` in the returned `Result` is arbitrary, but the `Tokens(T)` in
+    # the returned result MUST contain the parser's input, with some tokens
+    # removed from the front proprtional to what was parsed.
+    #
+    # Example:
+    # ```
+    # hello = ParsesHello.new # inherits from Parser(Char, String)
+    # input = Tokens.from_string("Hello world!")
+    #
+    # result = hello.parse(input)
+    # result.value  # => "Hello"
+    # result.tokens # => [' ', 'w', 'o', 'r', 'l', 'd', '!']
+    #
+    # bad_input = Tokens.from_string("Good evening world!")
+    # hello.parse(bad_input) # raises ParserFail
+    # ```
+    abstract def parse(tokens : Tokens(T)) : Result(T, V)
+
+    # Same as `#parse`, but returns `nil` instead of raising `ParserFail`.
+    def parse?(tokens : Tokens(T)) : Result(T, V)?
+      self.parse(tokens)
+    rescue ParserFail
+      return nil
+    end
+
+    # Constructs an `Alt` parser with `self` and `other`.
+    def |(other : Parser(T, V)) : Alt(T, V)
+      Alt.new(self, other)
+    end
+
+    # Constructs a `Plus` parser with `self` and `other`.
+    def +(other : Parser(T, U)) : Plus(T, V, U) forall U
+      Plus.new(self, other)
+    end
+
+    # Constructs a `Left` parser with `self` and `other`.
+    def <<(other : Parser(T, U)) : Left(T, V, U) forall U
+      Left.new(self, other)
+    end
+
+    # Constructs a `Right` parser with `self` and `other`.
+    def >>(other : Parser(T, U)) : Right(T, V, U) forall U
+      Right.new(self, other)
+    end
+
+    # Constructs an `Assert` parser with `self` and the given block.
+    def assert(&block : V -> Bool) : Assert(T, V)
+      Assert.new(self, &block)
+    end
+
+    # Constructs an `Assert` parser with `self` and the given proc.
+    def assert(f : V -> Bool) : Assert(T, V)
+      Assert.new(self, &f)
+    end
+
+    # Constructs a `Map` parser with `self` and the given block.
+    def map(&block : V -> U) : Map(T, V, U) forall U
+      Map.new(self, &block)
+    end
+
+    # Constructs a `Map` parser with `self` and the given proc.
+    def map(f : V -> U) : Map(T, V, U) forall U
+      Map.new(self, &f)
+    end
+
+    # Constructs a `Recover` parser with `self` and the given `V`.
+    def recover(default : V) : Recover(T, V)
+      Recover.new(self, default)
+    end
+  end
+end
+
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