diff options
| -rw-r--r-- | users/fcuny/exp/monkey/pkg/lexer/lexer.go | 114 | ||||
| -rw-r--r-- | users/fcuny/exp/monkey/pkg/lexer/lexer_test.go | 104 |
2 files changed, 218 insertions, 0 deletions
diff --git a/users/fcuny/exp/monkey/pkg/lexer/lexer.go b/users/fcuny/exp/monkey/pkg/lexer/lexer.go new file mode 100644 index 0000000..fc29371 --- /dev/null +++ b/users/fcuny/exp/monkey/pkg/lexer/lexer.go @@ -0,0 +1,114 @@ +package lexer + +import "monkey/pkg/token" + +// Lexer represents the lexer +type Lexer struct { + input string + // current position in input + position int + // current reading position in input (after a char) + readPosition int + // current character under examination + ch byte +} + +// New returns a new lexer +func New(input string) *Lexer { + l := &Lexer{input: input} + l.readChar() + return l +} + +// Read the current character and advances our position in the input string. +func (l *Lexer) readChar() { + // if we've reached the end of the input, we set the current character to 0, + // which is the ASCII code for NUL. + if l.readPosition >= len(l.input) { + l.ch = 0 + } else { + l.ch = l.input[l.readPosition] + } + l.position = l.readPosition + l.readPosition++ +} + +func (l *Lexer) readIdentifier() string { + position := l.position + for isLetter(l.ch) { + l.readChar() + } + return l.input[position:l.position] +} + +func (l *Lexer) readNumber() string { + position := l.position + for isDigit(l.ch) { + l.readChar() + } + return l.input[position:l.position] +} + +// we don't care about white space characters, we skip them when we find them. +func (l *Lexer) skipWhitespace() { + for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' { + l.readChar() + } +} + +// NextToken reads the next token from the lexer and returns the current token. +func (l *Lexer) NextToken() token.Token { + var tok token.Token + + l.skipWhitespace() + + switch l.ch { + case '=': + tok = newToken(token.ASSIGN, l.ch) + case '+': + tok = newToken(token.PLUS, l.ch) + case ';': + tok = newToken(token.SEMICOLON, l.ch) + case ',': + tok = newToken(token.COMMA, l.ch) + case '(': + tok = newToken(token.LPAREN, l.ch) + case ')': + tok = newToken(token.RPAREN, l.ch) + case '{': + tok = newToken(token.LBRACE, l.ch) + case '}': + tok = newToken(token.RBRACE, l.ch) + case 0: + tok.Literal = "" + tok.Type = token.EOF + default: + if isLetter(l.ch) { + tok.Literal = l.readIdentifier() + tok.Type = token.LookupIdent(tok.Literal) + return tok + } else if isDigit(l.ch) { + tok.Type = token.INT + tok.Literal = l.readNumber() + return tok + } else { + tok = newToken(token.ILLEGAL, l.ch) + } + + } + + l.readChar() + return tok +} + +func newToken(tokenType token.TokenType, ch byte) token.Token { + return token.Token{Type: tokenType, Literal: string(ch)} +} + +func isLetter(ch byte) bool { + return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' +} + +func isDigit(ch byte) bool { + return '0' <= ch && ch <= '9' +} diff --git a/users/fcuny/exp/monkey/pkg/lexer/lexer_test.go b/users/fcuny/exp/monkey/pkg/lexer/lexer_test.go new file mode 100644 index 0000000..73b27fb --- /dev/null +++ b/users/fcuny/exp/monkey/pkg/lexer/lexer_test.go @@ -0,0 +1,104 @@ +package lexer + +import ( + "monkey/pkg/token" + "testing" +) + +func TestNextTokenBasic(t *testing.T) { + input := `=+(){},;` + + tests := []struct { + expectedType token.TokenType + expectedLiteral string + }{ + {token.ASSIGN, "="}, + {token.PLUS, "+"}, + {token.LPAREN, "("}, + {token.RPAREN, ")"}, + {token.LBRACE, "{"}, + {token.RBRACE, "}"}, + {token.COMMA, ","}, + {token.SEMICOLON, ";"}, + } + + l := New(input) + + for i, tt := range tests { + tok := l.NextToken() + if tok.Type != tt.expectedType { + t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got=%q", i, tt.expectedType, tok.Type) + } + + if tok.Literal != tt.expectedLiteral { + t.Fatalf("tests[%d] - tokenliteral wrong. expected=%q, got=%q", i, tt.expectedLiteral, tok.Literal) + } + } +} + +func TestNextTokenMonkey(t *testing.T) { + input := `let five = 5; +let ten = 10; + +let add = fn(x, y) { + x + y +}; + +let result = add(five, ten);` + + tests := []struct { + expectedType token.TokenType + expectedLiteral string + }{ + {token.LET, "let"}, + {token.IDENT, "five"}, + {token.ASSIGN, "="}, + {token.INT, "5"}, + {token.SEMICOLON, ";"}, + + {token.LET, "let"}, + {token.IDENT, "ten"}, + {token.ASSIGN, "="}, + {token.INT, "10"}, + {token.SEMICOLON, ";"}, + + {token.LET, "let"}, + {token.IDENT, "add"}, + {token.ASSIGN, "="}, + {token.FUNCTION, "fn"}, + {token.LPAREN, "("}, + {token.IDENT, "x"}, + {token.COMMA, ","}, + {token.IDENT, "y"}, + {token.RPAREN, ")"}, + {token.LBRACE, "{"}, + {token.IDENT, "x"}, + {token.PLUS, "+"}, + {token.IDENT, "y"}, + {token.RBRACE, "}"}, + {token.SEMICOLON, ";"}, + + {token.LET, "let"}, + {token.IDENT, "result"}, + {token.ASSIGN, "="}, + {token.IDENT, "add"}, + {token.LPAREN, "("}, + {token.IDENT, "five"}, + {token.COMMA, ","}, + {token.IDENT, "ten"}, + {token.RPAREN, ")"}, + {token.SEMICOLON, ";"}, + } + + l := New(input) + for i, tt := range tests { + tok := l.NextToken() + if tok.Type != tt.expectedType { + t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got=%q", i, tt.expectedType, tok.Type) + } + + if tok.Literal != tt.expectedLiteral { + t.Fatalf("tests[%d] - tokenliteral wrong. expected=%q, got=%q", i, tt.expectedLiteral, tok.Literal) + } + } +} |