% Calculator.Txl - simple numerical expression evaluator

include "expr-grammar.Grm"

% Part 2.  Transformation rules
rule main
    replace [expression]
        E [expression]
    construct NewE [expression]
        E [resolveAddition] [resolveSubtraction] [resolveMultiplication] 
          [resolveDivision] [resolveParentheses]
    where not
        NewE [= E]
    by
        NewE
end rule

rule resolveAddition
    replace [expression]
        N1 [number] + N2 [number]
    by
        N1 [+ N2]
end rule

rule resolveSubtraction
    replace [expression]
        N1 [number] - N2 [number]
    by
        N1 [- N2]
end rule 

rule resolveMultiplication
    replace [term]
        N1 [number] * N2 [number]
    by
        N1 [* N2]
end rule 

rule resolveDivision
    replace [term]
        N1 [number] / N2 [number]
    by
        N1 [/ N2]
end rule

rule resolveParentheses
    replace [primary]
        ( N [number] )
    by
        N
end rule