In Haskell Language write matchEmpty, which determines whether the language for a regular -- expression includes the empty string. matchEmpty :: RE symbol -> Bool matchEmpty = ? -- Note that the type signature does not restrict symbol to types with -- equality testing, so we cannot use match or match' to check whether the -- empty string is allowed. -- -- matchEmpty r = match r [] -- type error -- -- Similarly, we cannot use generate' and check whether the first string -- it provides is the empty string. -- -- Finally, while generate has the proper type, we cannot use it to write a -- function that always terminates, as we cannot conclude that the empty -- string is not present until we have examined every string. -- -- *HW3> matchEmpty (getRE "e") -- True -- *HW3> matchEmpty (getRE "abc*") -- False -- *HW3> matchEmpty (getRE "a*") -- True -- *HW3> matchEmpty (getRE "0") -- False -- *HW3> matchEmpty (getRE "0*") -- True NOTE: Above are a few examples of what the output will look like. All that needs to be done is matchEmpty needs to be defined where the question mark is.
In Haskell Language write matchEmpty, which determines whether the language for a regular -- expression includes the empty string. matchEmpty :: RE symbol -> Bool matchEmpty = ? -- Note that the type signature does not restrict symbol to types with -- equality testing, so we cannot use match or match' to check whether the -- empty string is allowed. -- -- matchEmpty r = match r [] -- type error -- -- Similarly, we cannot use generate' and check whether the first string -- it provides is the empty string. -- -- Finally, while generate has the proper type, we cannot use it to write a -- function that always terminates, as we cannot conclude that the empty -- string is not present until we have examined every string. -- -- *HW3> matchEmpty (getRE "e") -- True -- *HW3> matchEmpty (getRE "abc*") -- False -- *HW3> matchEmpty (getRE "a*") -- True -- *HW3> matchEmpty (getRE "0") -- False -- *HW3> matchEmpty (getRE "0*") -- True NOTE: Above are a few examples of what the output will look like. All that needs to be done is matchEmpty needs to be defined where the question mark is.
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
Related questions
Question
In Haskell Language write matchEmpty, which determines whether the language for a regular
-- expression includes the empty string.
matchEmpty :: RE symbol -> Bool
matchEmpty = ?
-- Note that the type signature does not restrict symbol to types with
-- equality testing, so we cannot use match or match' to check whether the
-- empty string is allowed.
--
-- matchEmpty r = match r [] -- type error
--
-- Similarly, we cannot use generate' and check whether the first string
-- it provides is the empty string.
--
-- Finally, while generate has the proper type, we cannot use it to write a
-- function that always terminates, as we cannot conclude that the empty
-- string is not present until we have examined every string.
--
-- *HW3> matchEmpty (getRE "e")
-- True
-- *HW3> matchEmpty (getRE "abc*")
-- False
-- *HW3> matchEmpty (getRE "a*")
-- True
-- *HW3> matchEmpty (getRE "0")
-- False
-- *HW3> matchEmpty (getRE "0*")
-- True
-- expression includes the empty string.
matchEmpty :: RE symbol -> Bool
matchEmpty = ?
-- Note that the type signature does not restrict symbol to types with
-- equality testing, so we cannot use match or match' to check whether the
-- empty string is allowed.
--
-- matchEmpty r = match r [] -- type error
--
-- Similarly, we cannot use generate' and check whether the first string
-- it provides is the empty string.
--
-- Finally, while generate has the proper type, we cannot use it to write a
-- function that always terminates, as we cannot conclude that the empty
-- string is not present until we have examined every string.
--
-- *HW3> matchEmpty (getRE "e")
-- True
-- *HW3> matchEmpty (getRE "abc*")
-- False
-- *HW3> matchEmpty (getRE "a*")
-- True
-- *HW3> matchEmpty (getRE "0")
-- False
-- *HW3> matchEmpty (getRE "0*")
-- True
NOTE: Above are a few examples of what the output will look like. All that needs to be done is matchEmpty needs to be defined where the question mark is.
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