jmug/interpreter-in-go
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Parses infix expressions.

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Signed-off-by: jmug <u.g.a.mariano@gmail.com>
This commit is contained in:
Mariano Uvalle 2025-01-04 17:56:10 -08:00
parent f286a88039
commit 5fa7b2481a
4 changed files with 201 additions and 4 deletions
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17
pkg/ast/ast.go
View file

@ -131,7 +131,7 @@ func (il *IntegerLiteral) String() string {
}
type PrefixExpression struct {
Token token.Token
Token token.Token // The operator token
Operator string
Right Expression
}
@ -143,3 +143,18 @@ func (pe *PrefixExpression) TokenLiteral() string {
func (pe *PrefixExpression) String() string {
return "(" + pe.Operator + pe.Right.String() + ")"
}
type InfixExpression struct {
Token token.Token // The operator token
Operator string
Left Expression
Right Expression
}
func (ie *InfixExpression) expressionNode() {}
func (ie *InfixExpression) TokenLiteral() string {
return ie.Token.Literal
}
func (ie *InfixExpression) String() string {
return "(" + ie.Left.String() + " " + ie.Operator + " " + ie.Right.String() + ")"
}

35
pkg/parser/parser.go
View file

@ -30,10 +30,20 @@ func New(l *lexer.Lexer) *Parser {
prefixParseFns: map[token.TokenType]prefixParseFn{},
infixParseFns: map[token.TokenType]infixParseFn{},
}
// Prefix registrations
p.registerPrefix(token.IDENT, p.parseIdentifier)
p.registerPrefix(token.INT, p.parseIntegerLiteral)
p.registerPrefix(token.MINUS, p.parsePrefixExpression)
p.registerPrefix(token.BANG, p.parsePrefixExpression)
// Infix registrations
p.registerInfix(token.PLUS, p.parseInfixExpression)
p.registerInfix(token.MINUS, p.parseInfixExpression)
p.registerInfix(token.ASTERISK, p.parseInfixExpression)
p.registerInfix(token.SLASH, p.parseInfixExpression)
p.registerInfix(token.GT, p.parseInfixExpression)
p.registerInfix(token.LT, p.parseInfixExpression)
p.registerInfix(token.EQ, p.parseInfixExpression)
p.registerInfix(token.NOT_EQ, p.parseInfixExpression)
// TODO: figure out why this can't be done from `parseProgram`
p.nextToken()
p.nextToken()
@ -111,9 +121,16 @@ func (p *Parser) parseExpression(precedence int) ast.Expression {
p.noPrefixParseFnError(p.curToken.Type)
return nil
}
leftExpr := prefix()
return leftExpr
curExpr := prefix()
for !p.peekTokenIs(token.SEMICOLON) && precedence < p.peekPrecedence() {
infix := p.infixParseFns[p.peekToken.Type]
if infix == nil {
return curExpr
}
p.nextToken()
curExpr = infix(curExpr)
}
return curExpr
}
func (p *Parser) parseIdentifier() ast.Expression {
@ -141,6 +158,18 @@ func (p *Parser) parsePrefixExpression() ast.Expression {
return exp
}
func (p *Parser) parseInfixExpression(left ast.Expression) ast.Expression {
exp := &ast.InfixExpression{
Token: p.curToken,
Operator: p.curToken.Literal,
Left: left,
}
precedence := p.curPrecedence()
p.nextToken()
exp.Right = p.parseExpression(precedence)
return exp
}
func (p *Parser) curTokenIs(typ token.TokenType) bool {
return p.curToken.Type == typ
}

124
pkg/parser/parser_test.go
View file

@ -200,6 +200,130 @@ func TestParsingPrefixExpressions(t *testing.T) {
}
}
// parser/parser_test.go
func TestParsingInfixExpressions(t *testing.T) {
infixTests := []struct {
input string
leftValue int64
operator string
rightValue int64
}{
{"5 + 5;", 5, "+", 5},
{"5 - 5;", 5, "-", 5},
{"5 * 5;", 5, "*", 5},
{"5 / 5;", 5, "/", 5},
{"5 > 5;", 5, ">", 5},
{"5 < 5;", 5, "<", 5},
{"5 == 5;", 5, "==", 5},
{"5 != 5;", 5, "!=", 5},
}
for _, tt := range infixTests {
l := lexer.New(tt.input)
p := New(l)
program := p.ParseProgram()
checkParserErrors(t, p)
if len(program.Statements) != 1 {
t.Fatalf("program.Statements does not contain %d statements. got=%d\n",
1, len(program.Statements))
}
stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
if !ok {
t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T",
program.Statements[0])
}
exp, ok := stmt.Expression.(*ast.InfixExpression)
if !ok {
t.Fatalf("exp is not ast.InfixExpression. got=%T", stmt.Expression)
}
if !testIntegerLiteral(t, exp.Left, tt.leftValue) {
return
}
if exp.Operator != tt.operator {
t.Fatalf("exp.Operator is not '%s'. got=%s",
tt.operator, exp.Operator)
}
if !testIntegerLiteral(t, exp.Right, tt.rightValue) {
return
}
}
}
func TestOperatorPrecedenceParsing(t *testing.T) {
tests := []struct {
input string
expected string
}{
{
"-a * b",
"((-a) * b)",
},
{
"!-a",
"(!(-a))",
},
{
"a + b + c",
"((a + b) + c)",
},
{
"a + b - c",
"((a + b) - c)",
},
{
"a * b * c",
"((a * b) * c)",
},
{
"a * b / c",
"((a * b) / c)",
},
{
"a + b / c",
"(a + (b / c))",
},
{
"a + b * c + d / e - f",
"(((a + (b * c)) + (d / e)) - f)",
},
{
"3 + 4; -5 * 5",
"(3 + 4)((-5) * 5)",
},
{
"5 > 4 == 3 < 4",
"((5 > 4) == (3 < 4))",
},
{
"5 < 4 != 3 > 4",
"((5 < 4) != (3 > 4))",
},
{
"3 + 4 * 5 == 3 * 1 + 4 * 5",
"((3 + (4 * 5)) == ((3 * 1) + (4 * 5)))",
},
}
for _, tt := range tests {
l := lexer.New(tt.input)
p := New(l)
program := p.ParseProgram()
checkParserErrors(t, p)
actual := program.String()
if actual != tt.expected {
t.Errorf("expected=%q, got=%q", tt.expected, actual)
}
}
}
func testIntegerLiteral(t *testing.T, il ast.Expression, value int64) bool {
integ, ok := il.(*ast.IntegerLiteral)
if !ok {

29
pkg/parser/precedence.go
View file

@ -1,5 +1,9 @@
package parser
import (
"code.jmug.me/jmug/interpreter-in-go/pkg/token"
)
const (
_ int = iota
LOWEST
@ -10,3 +14,28 @@ const (
PREFIX // -X or !X
CALL // myFunction(X)
)
var precedences = map[token.TokenType]int{
token.EQ: EQUALS,
token.NOT_EQ: EQUALS,
token.GT: LESSGREATER,
token.LT: LESSGREATER,
token.PLUS: SUM,
token.MINUS: SUM,
token.ASTERISK: PRODUCT,
token.SLASH: PRODUCT,
}
func (p *Parser) peekPrecedence() int {
if pr, ok := precedences[p.peekToken.Type]; ok {
return pr
}
return LOWEST
}
func (p *Parser) curPrecedence() int {
if pr, ok := precedences[p.curToken.Type]; ok {
return pr
}
return LOWEST
}