Sequence, +, and variants

1 files changed, 55 insertions, 1 deletions

diff --git a/src/parcom/parser.cr b/src/parcom/parser.cr
index b78ab77..fcfe292 100644
--- a/src/parcom/parser.cr
+++ b/src/parcom/parser.cr
@@ -86,6 +86,32 @@ module Parcom
       Parser(T, T).satisfy { |x| x == token }.named("Token <#{token}>")
     end
 
+    # Creates a parser from an array of parsers that parses with
+    # each of them in sequence. The results of all parsers are returned
+    # in an array. If any of the parsers fail, the whole parser fails.
+    # TODO: allow support for Iterable(Parser(T, U))
+    def self.sequence(ps : Array(Parser(T, U))) : Parser(T, Array(U))
+      Parser(T, Array(U)).new("Sequence: #{ps.map(&.name)}") do |tokens|
+        values = [] of U
+        ps.each do |p|
+          result = p.parse(tokens)
+          values << result.value
+          tokens = result.tokens
+        end
+        Result.new(tokens, values)
+      end
+    end
+
+    # Creates a parser from an array of `T` that tries to parser
+    # each member of the array in sequence. An identical array is
+    # returned on success. If any of the tokens are absent, the
+    # whole parser fails.
+    # TODO: allow support for Iterable(T)
+    def self.token_sequence(ts : Array(T)) : Parser(T, Array(T))
+      ps = ts.map{ |t| Parser(T, T).token(t) }
+      Parser(T, T).sequence(ps).named("Token Sequence: #{ts}")
+    end
+
     # Creates a new parser from a `Proc`.
     # The `Proc` should have the properties outlined above.
     def initialize(@name : String, @f : Tokens(T) -> Result(T, U))
@@ -157,9 +183,13 @@ module Parcom
       map(block)
     end
 
+    # Creates a new parser from `self` and another parser that will
+    # try to parse with either of them. If the first parser succeeds,
+    # it will return the result of the first parser. Otherwise, it will
+    # return the result of the second parser.
     def |(p2 : Parser(T, U)) : Parser(T, U)
       p1 = self
-      Parser(T, U).new("#{p1.name} or #{p2.name}") do |tokens|
+      Parser(T, U).new("#{p1.name} | #{p2.name}") do |tokens|
         p1.parse(tokens)
       rescue ParserFail
         p2.parse(tokens)
@@ -187,6 +217,30 @@ module Parcom
         Result.new(new_tokens, new_value)
       end
     end
+
+    # Creates a new parser from `self` and another parser that will
+    # try to parse with both parsers and return both results. If either
+    # sub-parser fails, the whole parser fails.
+    def +(p2 : Parser(T, V)) : Parser(T, {U, V}) forall V
+      p1 = self
+      Parser(T, {U, V}).new("#{p1.name} + #{p2.name}") do |tokens|
+        r1 = p1.parse(tokens)
+        r2 = p2.parse(r1.tokens)
+        Result.new(r2.tokens, {r1.value, r2.value})
+      end
+    end
+
+    # Same as `#+`, but discards the second parser's result.
+    def <<(p2 : Parser(T, V)) : Parser(T, U) forall V
+      p1 = self
+      (p1 + p2).map(&.first).named("#{p1.name} << #{p2.name}")
+    end
+
+    # Same as `#+`, but discards the first parser's result.
+    def >>(p2 : Parser(T, V)) : Parser(T, V) forall V
+      p1 = self
+      (p1 + p2).map(&.last).named("#{p1.name} >> #{p2.name}")
+    end
   end
 end