/
evaluator.go
157 lines (136 loc) · 3.37 KB
/
evaluator.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
package evaluator
import (
"monkey_interpreter/ast"
"monkey_interpreter/object"
)
var (
NULL = &object.Null{}
TRUE = &object.Boolean{Value: true}
FALSE = &object.Boolean{Value: false}
)
func Eval(node ast.Node) object.Object {
switch node := node.(type) {
// statements
case *ast.Program:
return evalStatements(node.Statements)
case *ast.ExpressionStatement:
return Eval(node.Expression)
case *ast.BlockStatement:
return evalStatements(node.Statements)
// expressions
case *ast.IntegerLiteral:
return &object.Integer{Value: node.Value}
case *ast.Boolean:
return nativeBoolToBooleanObject(node.Value)
case *ast.PrefixExpression:
right := Eval(node.Right)
return evalPrefixExpression(node.Operator, right)
case *ast.InfixExpression:
left := Eval(node.Left)
right := Eval(node.Right)
return evalInfixExpression(node.Operator, left, right)
case *ast.IfExpression:
return evalIfExpression(node)
}
return nil
}
func evalStatements(stmts []ast.Statement) object.Object {
var result object.Object
for _, statement := range stmts {
result = Eval(statement)
}
return result
}
func evalPrefixExpression(operator string, right object.Object) object.Object {
switch operator {
case "!":
return evalBangOperatorExpression(right)
case "-":
return evalMinusPrefixOperatorExpression(right)
default:
return NULL
}
}
func evalBangOperatorExpression(right object.Object) object.Object {
switch right {
case TRUE:
return FALSE
case FALSE:
return TRUE
case NULL:
return TRUE
default:
return FALSE
}
}
func evalMinusPrefixOperatorExpression(right object.Object) object.Object {
if right.Type() != object.INTEGER_OBJ {
return NULL
}
value := right.(*object.Integer).Value
return &object.Integer{Value: -value}
}
func evalInfixExpression(operator string, left, right object.Object) object.Object {
switch {
case left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ:
return evalIntegerInfixExpression(operator, left, right)
case operator == "==":
return nativeBoolToBooleanObject(left == right)
case operator == "!=":
return nativeBoolToBooleanObject(left != right)
default:
return NULL
}
}
func evalIntegerInfixExpression(operator string, left, right object.Object) object.Object {
leftVal := left.(*object.Integer).Value
rightVal := right.(*object.Integer).Value
switch operator {
case "+":
return &object.Integer{Value: leftVal + rightVal}
case "-":
return &object.Integer{Value: leftVal - rightVal}
case "*":
return &object.Integer{Value: leftVal * rightVal}
case "/":
return &object.Integer{Value: leftVal / rightVal}
case "<":
return nativeBoolToBooleanObject(leftVal < rightVal)
case ">":
return nativeBoolToBooleanObject(leftVal > rightVal)
case "==":
return nativeBoolToBooleanObject(leftVal == rightVal)
case "!=":
return nativeBoolToBooleanObject(leftVal != rightVal)
default:
return NULL
}
}
func nativeBoolToBooleanObject(input bool) *object.Boolean {
if input {
return TRUE
}
return FALSE
}
func evalIfExpression(ie *ast.IfExpression) object.Object {
condition := Eval(ie.Condition)
if isTruthy(condition) {
return Eval(ie.Consequence)
} else if ie.Alternative != nil {
return Eval(ie.Alternative)
} else {
return NULL
}
}
func isTruthy(obj object.Object) bool {
switch obj {
case NULL:
return false
case TRUE:
return true
case FALSE:
return false
default:
return true
}
}