RosettaCodeData/Task/Arithmetic-evaluation/E/arithmetic-evaluation-1.e

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def eParser := <elang:syntax.makeEParser>
def LiteralExpr := <elang:evm.makeLiteralExpr>.asType()
def arithEvaluate(expr :String) {
def ast := eParser(expr)
def evalAST(ast) {
return switch (ast) {
match e`@a + @b` { evalAST(a) + evalAST(b) }
match e`@a - @b` { evalAST(a) - evalAST(b) }
match e`@a * @b` { evalAST(a) * evalAST(b) }
match e`@a / @b` { evalAST(a) / evalAST(b) }
match e`-@a` { -(evalAST(a)) }
match l :LiteralExpr { l.getValue() }
}
}
return evalAST(ast)
}