Implement map_const

1 files changed, 12 insertions, 0 deletions

diff --git a/src/parcom/parser.cr b/src/parcom/parser.cr
index fd161f9..57c7b44 100644
--- a/src/parcom/parser.cr
+++ b/src/parcom/parser.cr
@@ -207,6 +207,18 @@ module Parcom
       map(block)
     end
 
+    # Replaces the value inside `self` when parsing is successful.
+    # This is effectively a shorthand for the following:
+    # ```
+    # a = Parser.token('a')
+    # # These are equivalent:
+    # into42_map       = a.map { |_| 42 }
+    # into42_map_const = a.map_const(42)
+    # ```
+    def map_const(value : V) : Parser(T, V) forall V
+      map { |_| value }.named("#{@name} (const #{value})")
+    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