Implement Sequence

2 files changed, 43 insertions, 0 deletions

diff --git a/spec/parcom_spec.cr b/spec/parcom_spec.cr
index 57c5024..9051cb7 100644
--- a/spec/parcom_spec.cr
+++ b/spec/parcom_spec.cr
@@ -378,6 +378,32 @@ describe Optional do
   end
 end
 
+describe Sequence do
+  # HACK: ps has to be declared this way due to contravariance
+  # https://crystal-lang.org/reference/1.7/syntax_and_semantics/inheritance.html#covariance-and-contravariance
+  ps = [] of Parser(Char, Char)
+  ps = ps + "abcd".chars.map { |c| Token.new(c) }
+  p = Sequence.new(ps)
+
+  describe "#parse" do
+    it "runs each wrapped parser in order, returns each result" do
+      tokens = TokenStream.from_string("abcd")
+      result = p.parse(tokens)
+
+      result.value.should eq("abcd".chars)
+      result.tokens.empty?.should be_true
+    end
+
+    it "fails if any of the wrapped parsers fail" do
+      fail_strings = ["", "abed", "bbcd", "abce"]
+      fail_strings.each do |s|
+        tokens = TokenStream.from_string(s)
+        expect_raises(ParserException) { p.parse(tokens) }
+      end
+    end
+  end
+end
+
 describe Tokens do
   p = Tokens.new("test".chars)
 
diff --git a/src/parcom.cr b/src/parcom.cr
index 8d7c754..6fc6339 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -228,6 +228,23 @@ module Parcom
     end
   end
 
+  class Sequence(T, V) < Parser(T, Array(V))
+    def initialize(@ps : Iterable(Parser(T, V)))
+    end
+
+    def parse(tokens : TokenStream(T)) : Result(T, Array(V))
+      parsed = [] of V
+
+      @ps.each do |p|
+        r = p.parse(tokens)
+        parsed << r.value
+        tokens = r.tokens
+      end
+
+      Result.new(tokens, parsed)
+    end
+  end
+
   class Tokens(T) < Parser(T, Array(T))
     def initialize(@expected : Iterable(T))
     end