Step by Step solution about How to resolve the algorithm Idiomatically determine all the characters that can be used for symbols step by step in the Haskell programming language

File Overview:

This Haskell source code defines a set of functions to validate identifiers and type constructors in Haskell code.

Function Descriptions:

• isSymbolic: Checks if a character is a valid symbol, which can be an alpha-numeric character, underscore, or single quote.
• isConId: Checks if a string represents a valid type constructor identifier. It must start with an uppercase letter and be followed by zero or more symbolic characters.
• isVarId: Checks if a string represents a valid identifier. It must start with a lowercase letter and be followed by zero or more symbolic characters. It should not be a reserved word.
• isReserved: Checks if a string is a reserved word in Haskell.

Helper Functions:

• not: Negates a boolean value.
• null: Checks if a string is empty.
• isUpper: Checks if a character is uppercase.
• isLower: Checks if a character is lowercase.
• head: Returns the first character of a string.
• tail: Returns all characters of a string except the first.
• all: Checks if a predicate holds for all elements in a list or string.
• elem: Checks if an element is in a list.

Usage:

These functions can be used to validate identifiers and type constructors in Haskell code, ensuring they conform to the language's naming conventions. They can be particularly useful in static analysis tools or editors.

For example, the following code checks if a given string is a valid type constructor identifier:

let valid = isConId "MyType"

import Data.Char

-- predicate for valid symbol
isSymbolic ch = isAlphaNum ch || ch `elem` "_'"

-- predicate for valid type construtor
isConId s = and [ not (null s)
                , isUpper (head s)
                , all isSymbolic (tail s) ]

-- predicate for valid identifier
isVarId s = and [ not (null s)
                , isLower (head s)
                , all isSymbolic (tail s)
                , not (isReserved s) ]

-- predicate for reserved words
isReserved s = elem s ["case", "class", "data", "default", "deriving", "do "
                      , "else", "foreign", "if", "import", "in", "infix "
                      , "infixl", "infixr", "instance", "let", "module "
                      , "newtype", "of", "then", "type", "where", "_"