diff options
| -rw-r--r-- | spec/parcom_spec.cr | 33 | ||||
| -rw-r--r-- | src/parcom.cr | 26 |
2 files changed, 57 insertions, 2 deletions
diff --git a/spec/parcom_spec.cr b/spec/parcom_spec.cr index fd4b470..77a14dd 100644 --- a/spec/parcom_spec.cr +++ b/spec/parcom_spec.cr @@ -614,7 +614,38 @@ end pending StopIf do end -pending FirstOf do +describe FirstOf do + tokens = TokenStream.from_string("abcd") + letter_a = Token.new('a') + f = Flunk(Char, Char).new + + describe "#parse" do + it "cannot be instantiated with an empty Enumerable" do + expect_raises(ArgumentError) { FirstOf.new([] of Parser(Char, Char)) } + end + + it "uses the result of the first successful parser" do + a1 = [letter_a, f, f, f] of Parser(Char, Char) + a2 = [f, letter_a, f, f] of Parser(Char, Char) + a3 = [f, f, letter_a, f] of Parser(Char, Char) + a4 = [f, f, f, letter_a] of Parser(Char, Char) + + [a1, a2, a3, a4].each do |arr| + p = FirstOf.new(arr) + r = p.parse(tokens) + r.value.should eq('a') + r.tokens.should eq(tokens[1..]) + end + end + + it "only fails if no parsers are successful" do + x = Token.new('x') + y = Token.new('x') + z = Token.new('x') + p = FirstOf.new([x, y, z] of Parser(Char, Char)) + expect_raises(ParserException) { p.parse(tokens) } + end + end end pending SepBy do diff --git a/src/parcom.cr b/src/parcom.cr index cb3408a..2a61c2d 100644 --- a/src/parcom.cr +++ b/src/parcom.cr @@ -405,7 +405,31 @@ module Parcom class StopIf end - class FirstOf + class FirstOf(T, V) < Parser(T, V) + @p : Parser(T, V) + + def initialize(ps : Iterable(Parser(T, V))) + ps_iter = ps.each + p = ps_iter.next + + if p.is_a?(Iterator::Stop) + raise ArgumentError.new("FirstOf requires atleast one parser, got none") + end + + @p = p + p = ps_iter.next + + until p.is_a?(Iterator::Stop) + @p = @p | p + p = ps_iter.next + end + end + + def parse(tokens : TokenStream(T)) : Result(T, V) + @p.parse(tokens) + rescue ex : ParserException + raise ParserException.new("FirstOf: #{ex.message}") + end end class SepBy |