Implement Exactly + extra test for Sequence

2 files changed, 60 insertions, 2 deletions

diff --git a/spec/parcom_spec.cr b/spec/parcom_spec.cr
index 9051cb7..713445f 100644
--- a/spec/parcom_spec.cr
+++ b/spec/parcom_spec.cr
@@ -401,6 +401,15 @@ describe Sequence do
         expect_raises(ParserException) { p.parse(tokens) }
       end
     end
+
+    it "succeeds and returns empty array if parser iterable is empty" do
+      tokens = TokenStream.from_string("abcd")
+      empty_p = Sequence.new([] of Parser(Char, Char))
+      result = empty_p.parse(tokens)
+
+      result.value.empty?.should be_true
+      result.tokens.should eq(tokens)
+    end
   end
 end
 
@@ -480,7 +489,46 @@ describe Some do
   end
 end
 
-pending Exactly do
+describe Exactly do
+  letter_a = Token.new('a')
+  tokens = TokenStream.from_string("aaabcd")
+
+  describe "#parse" do
+    it "tries to parse exactly n of the wrapper parser" do
+      p = Exactly.new(3, letter_a)
+      result = p.parse(tokens)
+
+      result.value.should eq("aaa".chars)
+      result.tokens.should eq(tokens[3..])
+    end
+
+    it "always succeeds with an empty array if n < 1" do
+      p = Exactly.new(0, letter_a)
+      result = p.parse(tokens)
+
+      result.value.empty?.should be_true
+      result.tokens.should eq(tokens)
+
+      p = Exactly.new(-42, letter_a)
+      result = p.parse(tokens)
+
+      result.value.empty?.should be_true
+      result.tokens.should eq(tokens)
+    end
+
+    it "does not take extra matching tokens" do
+      p = Exactly.new(2, letter_a)
+      result = p.parse(tokens)
+
+      result.value.should eq("aa".chars)
+      result.tokens.should eq(tokens[2..])
+    end
+
+    it "fails if there are not enough matching tokens" do
+      p = Exactly.new(60, letter_a)
+      expect_raises(ParserException) { p.parse(tokens) }
+    end
+  end
 end
 
 pending AtLeast do
diff --git a/src/parcom.cr b/src/parcom.cr
index d7e6682..c7f4012 100644
--- a/src/parcom.cr
+++ b/src/parcom.cr
@@ -295,7 +295,17 @@ module Parcom
     end
   end
 
-  class Exactly
+  class Exactly(T, V) < Parser(T, Array(V))
+    @p : Sequence(T, V)
+
+    def initialize(i : Int, p : Parser(T, V))
+      i = i.negative? ? 0 : i
+      @p = Sequence.new(([p] of Parser(T, V)) * i)
+    end
+
+    def parse(tokens : TokenStream(T)) : Result(T, Array(V))
+      @p.parse(tokens)
+    end
   end
 
   class AtLeast