tijani
a170eb4450
git-svn-id: https://svn.tlawal.org/svn/monkey@47 f6afcba9-9ef1-4bdd-9b72-7484f5705bac
90 lines
1.6 KiB
Go
90 lines
1.6 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 eval_statements(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 native_bool_to_boolean_object(node.Value)
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case *ast.PrefixExpression:
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right := Eval(node.Right)
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return eval_prefix_expression(node.Operator, right)
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}
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return nil
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}
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func eval_statements(statements []ast.Statement) object.Object {
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var result object.Object
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for _, statement := range statements {
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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 native_bool_to_boolean_object(input bool) *object.Boolean {
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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 eval_prefix_expression(operator string, right object.Object) object.Object {
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switch operator {
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case "!":
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return eval_bang_operator_expression(right)
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case "-":
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return eval_minus_prefix_operator_expression(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 eval_bang_operator_expression(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 eval_minus_prefix_operator_expression(right object.Object) object.Object {
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if right.Type() != object.INTEGER_OBJECT{
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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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