haskell - datatype conversion without using buildExpressionParser -

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I am stuck at a point in changing the expression for the user's datatype

I was using biuldExpressionParser , but I did the following by using simple parser and recursive 

  openBrace = char '(' CloseBrace :: GenParser char st char Closebrace = char ')' bracketxprod = spaces & gt; & Gt; OpenBrace expr & lt; - Expression parser spaces & gt; & Gt; CloseBrace return expr

bracketExpr will return the expression entered into my own datatype

To change it into my datatype, If the expression is a number or a variable as follows: 

  expressionParser = negate1 & lt; | & Gt; Number & lt; | & Gt; Variable - & lt; | & Gt; Add & lt ;? & Gt; "Simple expression" negate1 :: parser xp negate1 = do {char '-'; Ds & lt; - Number; Return (Xprunge (DS)) & lt ;? & Gt; "Disclaimer" variable :: parser express Variable = Do {DS & LT; - many 1 (letter & lt;; & gt; digits); Return (XVVR DS)}

edition, I tried to isolate the expression using sepBy but I have to face many issues.

If I am unable to proceed from here (Express 1) (Xprp 2)

If you want to write a parser with the connectors Parser, which you need to think first in terms of high-level rules, here is a skeleton parser in Parsec; It does not meets 100% of your needs because all operators are similarities and right-cooperatives, while you may want different bias and left-collaboration. However, this is the basic way to write a parser: 

  import text. Reader Import Text. Paragraph import data. Client (Digit) - Basic Data Type Data Expr = Op Char Expr XP | N integer derived (show) type parser x = parsec string () x - reverse-sequenced & gt; & Gt ;, bracketed `and 'white-wrench` (<< lt;) :: Moneda M => M X - & gt; Y - & gt; MX MX & lt; & Lt; My = mx & gt; & Gt; = \ X - & gt; My & gt; & Gt; Return x infixel 1 & lt; & Lt; Fielded :: Parser E - & gt; Parser e brackets and e = four '('> '>' white ');' whitespaced :: Parser e - & gt; Parser e whitespace e = space & gt; & Gt; E & lt; & Lt; Space Number :: Parsons Express Number = Do C & LT; - Anof "123456789" - Can be reserved for the Octal / Hexadecimal CS of major 0 - Return of many digits (N (read (C: CS)) Operator :: Parser Expr operator = do e1 & lt; - expr_no_op o & Lt; - whitespaced (oneOf "+ * / -") e2 & lt; - expression returns (op o e1 e2) expr_no_op :: parser expression expr_no_op = whitespaced (try number & lt;; & gt expression expression: expression :: Expression expression: Express expression = whitespaced (try operator  | Try & lt; | & gt; Fielded Expressions)

Note that you token (top, only 'number') and then "this Try combining that with ; otherwise try ... "syntax, also keep in mind that to prevent operator Do not take the expression as your first argument otherwise you should loop it into a operator -> expression -> operator parsing "left factorial "Is called.


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