Documentation for Phrase

2 files changed, 34 insertions, 1 deletions

diff --git a/src/parcom.cr b/src/parcom.cr
index aa7abba..6c17596 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -81,7 +81,7 @@ module Parcom
     end
   end
 
-  class Phrase(T, V)
+  class Phrase(T, V) < Parser(T, V)
     @p : Map(T, {V, Nil}, V)
 
     def initialize(p : Parser(T, V))
diff --git a/src/parcom/phrase.cr b/src/parcom/phrase.cr
new file mode 100644
index 0000000..1996fd4
--- /dev/null
+++ b/src/parcom/phrase.cr
@@ -0,0 +1,33 @@
+require "./parser.cr"
+require "./eof.cr"
+require "./map.cr"
+
+module Parcom
+  # `Phrase` is a `Parser` that tries to parse with another parser,
+  # but will fail if any of the input has not been consumed.
+  #
+  # Example:
+  # ```
+  # letter_a = Token.new('a')
+  # tokens = Tokens.from_string("aaa")
+  # one_a = Phrase(Char, Char).new(letter_a)
+  # result = one_a.parse(tokens) # This fails
+  # ```
+  class Phrase(T, V) < Parser(T, V)
+    @p : Map(T, {V, Nil}, V)
+
+    # Accepts the parser to parse with.
+    def initialize(p : Parser(T, V))
+      @p = (p + EOF(T).new).map &.first
+    end
+
+    # Tries to parse with the given parser, fails if there
+    # is any un-parsed input remaining.
+    def parse(tokens : Tokens(T)) : Result(T, V)
+      @p.parse(tokens)
+    rescue ex : ParserFail
+      raise ParserFail.new("Phrase: #{ex.message}")
+    end
+  end
+end
+