129 lines
2.8 KiB
Go
129 lines
2.8 KiB
Go
package evaluator
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import (
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"monkey/ast"
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"monkey/object"
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)
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var (
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NULL = &object.Null{}
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TRUE = &object.Boolean{Value: true}
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FALSE = &object.Boolean{Value: false}
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)
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func Eval(node ast.Node) object.Object {
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switch node := node.(type) {
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// Statements
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case *ast.Program:
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return evalStatements(node.Statements)
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case *ast.ExpressionStatement:
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return Eval(node.Expression)
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// Expressions
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case *ast.IntegerLiteral:
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return &object.Integer{Value: node.Value}
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case *ast.Boolean:
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return nativeBoolToBooleanObject(node.Value)
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case *ast.PrefixExpression:
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right := Eval(node.Right)
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return evalPrefixExpression(node.Operator, right)
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case *ast.InfixExpression:
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left := Eval(node.Left)
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right := Eval(node.Right)
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return evalInfixExpression(node.Operator, left, right)
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}
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return nil
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}
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func evalStatements(stmts []ast.Statement) object.Object {
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var result object.Object
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for _, statement := range stmts {
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result = Eval(statement)
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}
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return result
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}
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func nativeBoolToBooleanObject(input bool) object.Object {
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if input {
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return TRUE
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}
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return FALSE
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}
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func evalPrefixExpression(operator string, right object.Object) object.Object {
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switch operator {
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case "!":
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return evalBangOperatorExpression(right)
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case "-":
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return evalMinusPrefixOperatorExpression(right)
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default:
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return NULL
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}
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}
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func evalBangOperatorExpression(right object.Object) object.Object {
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switch right {
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case TRUE:
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return FALSE
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case FALSE:
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return TRUE
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case NULL:
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return TRUE
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default:
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return FALSE
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}
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}
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func evalMinusPrefixOperatorExpression(right object.Object) object.Object {
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if right.Type() != object.INTEGER_OBJ {
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return NULL
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}
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value := right.(*object.Integer).Value
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return &object.Integer{Value: -value}
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}
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func evalInfixExpression(operator string, left, right object.Object) object.Object {
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switch {
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case left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ:
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return evalIntegerInfixExpression(operator, left, right)
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case operator == "==":
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return nativeBoolToBooleanObject(left == right)
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case operator == "!=":
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return nativeBoolToBooleanObject(left != right)
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default:
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return NULL
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}
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}
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func evalIntegerInfixExpression(operator string, left, right object.Object) object.Object {
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leftVal := left.(*object.Integer).Value
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rightVal := right.(*object.Integer).Value
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switch operator {
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case "+":
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return &object.Integer{Value: leftVal + rightVal}
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case "-":
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return &object.Integer{Value: leftVal - rightVal}
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case "*":
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return &object.Integer{Value: leftVal * rightVal}
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case "/":
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return &object.Integer{Value: leftVal / rightVal}
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case "<":
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return nativeBoolToBooleanObject(leftVal < rightVal)
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case ">":
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return nativeBoolToBooleanObject(leftVal > rightVal)
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case "==":
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return nativeBoolToBooleanObject(leftVal == rightVal)
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case "!=":
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return nativeBoolToBooleanObject(leftVal != rightVal)
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default:
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return NULL
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}
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}
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