CS421 Lecture 6
CS421
Lecture
6
▶
Today
’
s class
▶
Today s
class
▶Regular Expressions
▶
Ocamllex
▶
Ocamllex
▶These slides are based on slides by Elsa Gunter, Mattox Beckman
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CS421 Lecture 6: Regular Expressions and Ocamllex - Prof. Elsa Gunter, Study notes of Computer Science
A set of lecture slides from cs421, a course on compilers at the university of x. The slides cover the topics of regular expressions and ocamllex, a lexer generator for the ocaml programming language. Examples of regular expressions and their implementation in ocamllex, as well as explanations of the mechanics of using ocamllex to create lexical analyzers.
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CS421 Lecture 6CS
Lecture 6
Today’s class ▶
Today s class
▶
Regular Expressions ▶
Ocamllex ▶
Ocamllex
▶^
These slides are based on slides by Elsa Gunter, Mattox Beckman
Overview of OcamllexOverview
of Ocamllex
Regular Expression ExamplesRegular
Expression Examples
Regular Expression ExamplesRegular
Expression Examples
▶
Keywords
y
▶
Operators ▶
Identifiers ▶
Int literals
Regular Expression ExampleRegular
Expression Example
Float-point Literal ▶
Float point Literal
Regular Expression ExampleRegular
Expression Example
New-Style Comments (//) ▶
New Style Comments (//) ▶
Old-Style Comments (/* … */)
Lexing with Reg ExprsLexing
with Reg Exprs
Create one large RE: ▶
Create one large RE: Th
dd
i
Th
en add actions
(cont ) (cont
Ambiguous cases: ▶
Ambiguous cases: ▶
Two tokens found, one longer ▶
Two tokens found, the same length
Ocamllex InputOcamllex
Input
▶
header and
trailer contain arbitrary
▶
header and
trailer contain arbitrary
ocaml code put at top an bottom of
l
.ml ▶
let
ident =
regexp ... Introduces
ident
g
p
for use in later regular expressions
MechanicsMechanics ▶
Put table of regular expressions and ▶
Put
table of regular expressions and
corresponding actions (written in ocaml)into a fileinto a file
.mll
Call ▶
Call
ocamllex .mll
P
d
O
l^
d
f^
l^
i^
l
P
roduces Ocaml code for a lexical analyzer in file .ml
Ocamllex InputOcamllex
Input
▶
ml contains one lexing ▶
.ml contains one lexingfunction per
entrypoint
Name of function is name given for ▶
Name of function is name given forentrypoint
Each entry point becomes an Ocaml ▶
Each entry point becomes an Ocamlfunction that takes
n+1 arguments, the
extra implicit last argument being of typeextra implicit last argument being of typeLexing.lexbuf
▶
arg
a
rgn are for use in
action
▶
arg1... a
rgn are for use in
action
Ocamllex Regular ExpressionOcamllex
Regular Expression
Single quoted characters for letters:
a
Single
quoted characters for letters: a
_: (underscore) matches any character
f^
i l
d
f fil
”^
k
eof: special
end_of_file
”^
marker
Concatenation: concatenation ▶
string
”: concatenation of sequence of
characters ▶
e
1
e
2
: choice
Ocamllex Regular ExpressionOcamllex
Regular Expression
▶
e #
e : the characters in
e
but not in
▶
e
1
e
: the characters in 2
e
1
but not in
e
2
;
e
1
and
e
2
must describe just sets
f^
h
t
of characters ▶
ident: abbreviation for earlier reg exp
g
p
in let
ident =
regexp
▶
e as
id: binds the result of
e
to
id to
▶
e
1
as
id: binds the result of
e
1
to
id to
be used in the associated
action
Ocamllex ManualOcamllex
Manual
More details can be found at ▶
More details can be found at h
l i
i^
f /
b/d
/^
l
http://caml.inria.fr/pub/docs/manual-
ocaml/manual026.html