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This document describes the Tiger project for EPITA students as of January 23, 2018. It is available under various forms:
More information is available on the EPITA Tiger Compiler Project Home Page.
Tiger is derived from a language introduced by Andrew Appel in his book Modern Compiler Implementation. This document is by no means sufficient to produce an actual Tiger compiler, nor to understand compilation. You are strongly encouraged to buy and read Appel’s book: it is an excellent book.
There are several differences with the original book, the most important being that EPITA students have to implement this compiler in C++ and using modern object oriented programming techniques. You ought to buy the original book, nevertheless, pay extreme attention to implementing the version of the language specified below, not that of the book.
• Tiger Language Reference Manual: | The Tiger Language Definition | |
• Language Extensions: | Additional constructions used internally | |
• Predefined Entities: | Primitive Functions and Types | |
• Implementation: | The tc Tiger Compiler
| |
• The Reference Implementation: | The compiler of the LRDE | |
— The Detailed Node Listing — Tiger Language Reference Manual | ||
---|---|---|
• Lexical Specifications: | Tokens | |
• Syntactic Specifications: | EBNF grammar | |
• Semantics: | The meaning of Life, Universe and the rest | |
Semantics | ||
• Declarations: | The semantics of declarations | |
• Expressions: | The semantics of expressions | |
Declarations | ||
• Type Declarations: | Semantics of type constructions | |
• Variable Declarations: | Semantics of variable definitions | |
• Function Declarations: | Function and primitive declaration semantics | |
• Method Declarations: | Method declaration semantics | |
Language Extensions | ||
• Additional Lexical Specifications: | New Tokens | |
• Additional Syntactic Specifications: | EBNF grammar extension | |
• Additional Semantics: | Beyond Life, the Universe and Everything | |
Predefined Entities | ||
• Predefined Types: | Built-in types | |
• Predefined Functions: | Primitives | |
Implementation | ||
• Invoking tc: | Command line options | |
• Errors: | Handling invalid input | |
• Extensions: | Making extensions to your compiler | |
The Reference Implementation |
Next: Language Extensions, Previous: Top, Up: Top [Contents]
This document defines the Tiger language, derived from a language introduced by Andrew Appel in his “Modern Compiler Implementation” books (see Modern Compiler Implementation in The Tiger Compiler Project). We insist so that our students buy this book, so we refrained from publishing a complete description of the language. Unfortunately, recent editions of this series of book no longer address Tiger (see In Java - Second Edition in The Tiger Compiler Project), and therefore they no longer include a definition of the Tiger compiler. As a result, students were more inclined to xerox the books, rather than buying newer editions. To fight this trend, we decided to publish a complete definition of the language. Of course, the definition below is not a verbatim copy from the original language definition: these words are ours.
• Lexical Specifications: | Tokens | |
• Syntactic Specifications: | EBNF grammar | |
• Semantics: | The meaning of Life, Universe and the rest |
‘array’, ‘if’, ‘then’, ‘else’, ‘while’, ‘for’, ‘to’, ‘do’, ‘let’, ‘in’, ‘end’, ‘of’, ‘break’, ‘nil’, ‘function’, ‘var’, ‘type’, ‘import’ and ‘primitive’
The keywords ‘class’, ‘extends’, ‘method’ and ‘new’ are reserved for object-related constructions. They are valid keywords when the object extension of the language is enabled, and reserved words if this extension is disabled (i.e., they cannot be used as identifiers in object-less syntax).
‘,’, ‘:’, ‘;’, ‘(’, ‘)’, ‘[’, ‘]’, ‘{’, ‘}’, ‘.’, ‘+’, ‘-’, ‘*’, ‘/’, ‘=’, ‘<>’, ‘<’, ‘<=’, ‘>’, ‘>=’, ‘&’, ‘|’, and ‘:=’
Space and tabulations are the only white space characters supported. Both count as a single character when tracking locations.
End of lines are ‘\n\r’, and ‘\r\n’, and ‘\r’, and ‘\n’, freely intermixed.
The strings are ANSI-C strings: enclosed by ‘"’, with support for the following escapes:
control characters.
The character which code is num in octal. Valid character codes belong to an extended (8-bit) ASCII set, i.e. values between 0 and 255 in decimal (0 and 377 in octal). num is composed of exactly three octal characters, and any invalid value is a scan error.
The character which code is num in hexadecimal (upper case or lower case or mixed). num is composed of exactly 2 hexadecimal characters. Likewise, expected values belong to an extended (8-bit) ASCII set.
A single backslash.
A double quote.
If no rule above applies, this is an error.
All the other characters are plain characters and are to be included in the string. In particular, multi-line strings are allowed.
Like C comments, but can be nested:
Code /* Comment /* Nested comment */ Comment */ Code
Identifiers start with a letter, followed by any number of alphanumeric characters plus the underscore. Identifiers are case sensitive. Moreover, the special _main string is also accepted as a valid identifier.
id ::= letter { letter | digit | _ } | _main letter ::= a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z digit ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
There are only integers in Tiger.
integer ::= digit { digit } op ::= + | - | * | / | = | <> | > | < | >= | <= | & | |
Any other character is invalid.
Next: Semantics, Previous: Lexical Specifications, Up: Tiger Language Reference Manual [Contents]
We use Extended BNF, with ‘[’ and ‘]’ for zero or once, and ‘{’ and ‘}’ for any number of repetition including zero.
program ::= exp | decs
exp ::= # Literals. nil | integer | string # Array and record creations. | type-id [ exp ] of exp | type-id {[ id = exp { , id = exp } ] } # Object creation. | new type-id # Variables, field, elements of an array. | lvalue # Function call. | id ( [ exp { , exp }] ) # Method call. | lvalue . id ( [ exp { , exp }] ) # Operations. | - exp | exp op exp | ( exps ) # Assignment. | lvalue := exp # Control structures. | if exp then exp [else exp] | while exp do exp | for id := exp to exp do exp | break | let decs in exps end
lvalue ::= id | lvalue . id | lvalue [ exp ] exps ::= [ exp { ; exp } ]
decs ::= { dec } dec ::= # Type declaration. type id = ty # Class definition (alternative form). | class id [ extends type-id ] { classfields } # Variable declaration. | vardec # Function declaration. | function id ( tyfields ) [ : type-id ] = exp # Primitive declaration. | primitive id ( tyfields ) [ : type-id ] # Importing a set of declarations. | import string
vardec ::= var id [ : type-id ] := exp
classfields ::= { classfield } # Class fields. classfield ::= # Attribute declaration. vardec # Method declaration. | method id ( tyfields ) [ : type-id ] = exp
# Types. ty ::= # Type alias. type-id # Record type definition. | { tyfields } # Array type definition. | array of type-id # Class definition (canonical form). | class [ extends type-id ] { classfields } tyfields ::= [ id : type-id { , id : type-id } ] type-id ::= id
op ::= + | - | * | / | = | <> | > | < | >= | <= | & | |
Precedence of the op (high to low):
* / + - >= <= = <> < > & |
Comparison operators (<
, <=
, =
, <>
,
>
, >=
) are not associative. All the remaining operators
are left-associative.
Previous: Syntactic Specifications, Up: Tiger Language Reference Manual [Contents]
• Declarations: | The semantics of declarations | |
• Expressions: | The semantics of expressions |
Next: Expressions, Up: Semantics [Contents]
An import
clause denote the same expression where it was
(recursively) replaced by the set of declarations its corresponding
import-file contains. An import-file has the following syntax (see
Syntactic Specifications, for a definition of the symbols):
import-file ::= decs
Because the syntax is different, it is convenient to use another extension. We use *.tih for files to import, for instance:
/* fortytwo-fn.tih. */ function fortytwo() : int = 42
/* fortytwo-var.tih. */ import "fortytwo-fn.tih" var fortytwo := fortytwo()
/* fortytwo-main.tig. */ let import "fortytwo-var.tih" in print_int(fortytwo); print("\n") end
is rigorously equivalent to:
let function fortytwo() : int = 42 var fortytwo := fortytwo() in print_int(fortytwo); print("\n") end
There can never be a duplicate-name conflict between declarations from different files. For instance:
/* 1.tih */ function one() : int = 1
let import "1.tih" import "1.tih" in one() = one() end
is valid although
let function one() : int = 1 function one() : int = 1 in one() = one() end
is not: the function one
is defined twice in a row of function
declarations.
Importing a nonexistent file is an error. A imported file may not include itself, directly or indirectly. Both these errors must be diagnosed, with status set to 1 (see Errors).
When processing an import directive, the compiler starts looking for files in the current directory, then in all the directories of the include path, in order.
There are three name spaces: types, variables and functions. The original language definition features two: variables and functions share the same name space. The motivation, as noted by Sébastien Carlier, is that in FunTiger, in the second part of the book, functions can be assigned to variables:
let type a = {a : int} var a := 0 function a(a : a) : a = a{a = a.a} in a(a{a = a}) end
Three name spaces support is easier to implement.
• Type Declarations: | Semantics of type constructions | |
• Variable Declarations: | Semantics of variable definitions | |
• Function Declarations: | Function and primitive declaration semantics | |
• Method Declarations: | Method declaration semantics |
Next: Variable Declarations, Up: Declarations [Contents]
The size of the array does not belong to the type. Index of arrays starts from 0 and ends at size - 1.
let type int_array = array of int var table := int_array[100] of 0 in ... end
Arrays are initialized with the same instance of value. This leads to aliasing for entities with pointer semantics (strings, arrays and records).
let type rec = { val : int } type rec_arr = array of rec var table := rec_arr[2] of rec { val = 42 } in table[0].val := 51 /* Now table[1].val = 51. */ end
Use a loop to instantiate several initialization values.
let type rec = { val : int } type rec_arr = array of rec var table := rec_arr[2] of nil in for i := 0 to 1 do table[i] := rec { val = 42 }; table[0].val := 51 /* table[1].val = 42. */ end
Records are defined by a list of fields between braces. Fields are described as “fieldname : type-id” and are separated by a coma. Field names are unique for a given record type.
let type indexed_string = {index : int, value : string} in ... end
(See also Method Declarations.)
Classes define a set of attributes and methods. Empty classes are
valid. Attribute declaration is like variable declaration; method
declaration is similar to function declaration, but uses the keyword
method
instead of function
.
There are two ways to declare a class. The first version (known as
canonical) uses type
, and is similar to record and array
declaration :
let type Foo = class extends Object { var bar := 42 method baz() = print("Foo.\n") } in /* ... */ end
The second version (known as alternative or Appel’s) doesn’t make
use of type
, but introduces classes declarations directly. This
is the syntax described by Andrew Appel in his books:
let class Foo extends Object { var bar := 42 method baz() = print("Foo.\n") } in /* ... */ end
For simplicity reasons, constructs using the alternative syntax are considered as syntactic sugar for the canonical syntax, and are desugared by the parser into this first form, using the following transformation:
class Name [ extends Super ] { Classfields } => type Name = class [ extends Super ] { Classfields }
where Name, Super and Classfields are respectively the class name, the super class name and the contents of the class (attributes and methods) of the class.
In the rest of the section, Appel’s form will be often used, to offer a uniform reading with his books, but remember that the main syntax is the other one, and Appel’s syntax is to be desugared into the canonical one.
Declarations of class members follow the same rules as variable and function declarations: consecutive method declarations constitute a block (or chunk) of methods, while a block of attributes contains only a single one attribute declaration (several attribute declarations thus form several blocks). An extra rule holds for class members: there shall be no two attributes with the same name in the same class definition, nor two methods with the name.
let class duplicate_attrs { var a := 1 method m() = () /* Error, duplicate attribute in the same class. */ var a := 2 } class duplicate_meths { method m() = () var a := 1 /* Error, duplicate method in the same class. */ method m() = () } in end
Note that this last rule applies only to the strict scope of the class, not to the scopes of inner classes.
let type C = class { var a := 1 method m() = let type D = class { /* These members have same names as C's, but this is allowed since they are not in the same scope. */ var a := 1 method m() = () } in end } in end
Objects of a given class are created using the keyword new
.
There are no constructors in Tiger (nor destructors), so the
attributes are always initialized by the value given at their
declaration.
let class Foo { var bar := 42 method baz() = print("Foo.\n") } class Empty { } var foo1 : Foo := new Foo /* As for any variable, the type annotation is optional. */ var foo2 := new Foo in /* ... */ end
The access to a member (either an attribute or a method) of an object from outside the class uses the dotted notation (as in C++, Java, C#, etc.). There are no visibility qualifier/restriction (i.e., all attributes of an object accessible in the current scope are accessible in read and write modes), and all its methods can be called.
let class Foo { var bar := 42 method baz() = print("Foo.\n") } var foo := new Foo in print_int(foo.bar); foo.baz() end
To access to a member (either an attribute or a method) from within the
class where it is defined, use the self
identifier (equivalent to
C++’s Or Java’s this), which refers to the current instance of the
object.
let class Point2d { var row : int := 0 var col : int := 0 method print_row() = print_int(self.row) method print_col() = print_int(self.col) method print() = ( print("("); self.print_row(); print(", "); self.print_col(); print(")") ) } in /* ... */ end
The use of self
is mandatory to access a member of the class (or
of its super class(es)) from within the class. A variable or a method
not preceded by ‘self.
’ won’t be looked up in the scope of the
class.
let var a := 42 function m() = print("m()\n") class C { var a := 51 method m() = print("C.m()\n") method print_a() = (print_int(a); print("\n")) method print_self_a() = (print_int(self.a); print("\n")) method call_m() = m() method call_self_m() = self.m() } var c := new C in c.print_a(); /* Print `42'. */ c.print_self_a(); /* Print `51'. */ c.call_m(); /* Print `m()'. */ c.call_self_m() /* Print `C.m()'. */ end
self
cannot be used outside a method definition. In this
respect, self
cannot appear in a function or a class defined
within a method (except within a method defined therein, of course).
let type C = class { var a := 51 var b := self /* Invalid. */ method m () : int = let function f () : int = self.a /* Invalid. */ in f() + self.a /* Valid. */ end } var a := new C in a := self /* Invalid. */ end
self
is a read-only variable and cannot be assigned.
The Tiger language supports single inheritance thanks to the
keyword extends
, so that a class can inherit from another class
declared previously, or declared in the same block of class
declarations. A class with no manifest inheritance (no extends
statement following the class name) automatically inherits from the
built-in class Object
(this feature is an extension of Appel’s
object-oriented proposal).
Inclusion polymorphism is supported as well: when a class Y inherits from a class X (directly or through several inheritance links), any object of Y can be seen as an object of type X. Hence, objects have two types: the static type, known at compile time, and the dynamic (or exact) type, known at run time, which is a subtype of (or identical to) the static type. Therefore, an object of static type Y can be assigned to a variable of type X.
let /* Manifest inheritance from Object: an A is an Object. */ class A extends Object {} /* Implicit inheritance from Object: a B is an Object. */ class B {} /* C is an A. */ class C extends A {} var a : A := new A var b : B := new B var c1 : C := new C /* When the type is not given explicitly, it is inferred from the initialization; here, C2 has static and dynamic type C. */ var c2 := new C /* This variable has static type A, but dynamic type C. */ var c3 : A := new C in /* Allowed (upcast). */ a := c1 /* Forbidden (downcast). */ /* c2 := a */ end
As stated before, a class can inherit from a class1 declared previously (and visible in the scope), or from a class declared in the same block of type declarations (recall that a class declaration is in fact a type declaration). Recursive inheritance is not allowed.
let /* Allowed: A declared before B. */ class A {} class B extends A {} /* Allowed: C declared before D. */ class C {} var foo := -42 class D extends C {} /* Allowed: forward inheritance, with E and F in the same block. */ class F extends E {} class E {} /* Forbidden: forward inheritance, with G and H in different blocks. */ class H extends G {} var bar := 2501 class G {} /* Forbidden: recursive inheritance. */ class I extends J {} class J extends I {} /* Forbidden: recursive inheritance and forward inheritance with K and L in different blocks. */ class K extends L {} var baz := 2097 class L extends K {} /* Forbidden: M inherits from a non-class type. */ class M extends int {} in /* ... */ end
All members from the super classes (transitive closure of the “is a”
relationship) are accessible using the dotted notation, and the
identifier self
when they are used from within the class.
Attribute redefinition is not allowed: a class cannot define an attribute with the same name as an inherited attribute, even if it has the same type. Regarding method overriding, see Method Declarations.
Let us consider a block of type definitions. For each class of this block, any of its members (either attributes or methods) can reference any type introduced in scope of the block, including the class type enclosing the considered members.
let /* A block of types. */ class A { /* Valid forward reference to B, defined in the same block as the class enclosing this member. */ var b := new B } type t = int class B { /* Invalid forward reference to C, defined in another block (binding error). */ var c := new C } /* A block of variables. */ var v : t := 42 /* Another block of types. */ class C { } in end
However, a class member cannot reference another member defined in a class defined later in the program, in the current class or in a future class (except if the member referred to is in the same block as the referring member, hence in the same class, since a block of members cannot obviously span across two or more classes). And recall that class members can only reference previously defined class members, or members of the same block of members (e.g., a chunk of methods).
let /* A block of types. */ class X { var i := 1 /* Valid forward reference to self.o(), defined in the same block of methods. */ method m() : int = self.o() /* Invalid forward reference to self.p(), defined in another (future) block of methods (type error). */ method n() = self.p() /* Valid (backward) reference to self.i, defined earlier. */ method o() : int = self.i var j := 2 method p() = () var y := new Y /* Invalid forward reference to y.r(), defined in another (future) class (type error). */ method q() = self.y.r() } class Y { method r() = () } in end
To put it in a nutshell: within a chunk of types, forward references to classes are allowed, while forward references to members are limited to the block of members where the referring entity is defined.
Types can be recursive,
let type stringlist = {head : string, tail : stringlist} in ... end
or mutually recursive (if they are declared in the same chunk) in Tiger.
let type indexed_string = {index : int, value : string} type indexed_string_list = {head : indexed_string, tail : indexed_string_list} in ... end
but there shall be no cycle. This
let type a = b type b = a in ... end
is invalid.
Two types are equivalent iff they are issued from the same type construction (array or record construction, or primitive type). As in C, unlike Pascal, structural equivalence is rejected.
Type aliases do not build new types, hence they are equivalent.
let type a = int type b = int var a := 1 var b := 2 in a = b /* OK */ end
let type a = {foo : int} type b = {foo : int} var va := a{foo = 1} var vb := b{foo = 2} in va = vb end
is invalid, and must be rejected with exit status set to 5.
Next: Function Declarations, Previous: Type Declarations, Up: Declarations [Contents]
There are two forms of variable declarations in Tiger: the short one and the long one.
In the short form, only the name of the variable and the initial value of the variable are specified, the variable type is “inferred”.
let var foo := 1 /* foo is typed as an integer */ in ... end
In the long form, the type of the variable is specified. Since one
cannot infer a record type for nil
, the long form is mandated
when declaring a variable initialized to nil
.
let type foo = {foo : int} var bar : foo := nil /* Correct. */ var baz := nil /* Incorrect. */ in ... end
Next: Method Declarations, Previous: Variable Declarations, Up: Declarations [Contents]
To declare a function, provide its return value type:
let function not (i : int) : int = if i = 0 then 1 else 0 in ... end
A procedure has no value return type.
let function print_conditional(s : string, i : int) = if i then print(s) else print("error") in print_conditional("foo", 1) end
Functions can be recursive, but mutually recursive functions must be in the same sequence of function declarations (no other declaration should be placed between them).
See the semantics of function calls for the argument passing policy (see Expressions).
A primitive is a built-in function, i.e., a function which body is provided by the runtime system. See Predefined Functions, for the list of standard primitives. Aside from the lack of body, and henceforth the absence of translation, primitive declarations behave as function declarations. They share the same name space, and obey the same duplicate-name rule. For instance:
let primitive one() : int function one() : int = 1 in ... end
is invalid, and must be rejected with exit status set to 4.
Previous: Function Declarations, Up: Declarations [Contents]
When a method in a class overrides a method of a super class, the overridden method (in the super class) is no longer accessible. Dynamic dispatch is performed, using the exact type of the object (known at run time) to select the method according to this exact type.
However, the interface of the accessible attributes and callable methods remains restricted to the static interface (i.e., the one of the static type of the object).
let class Shape { /* Position. */ var row := 0 var col := 0 method print_row() = (print("row = "); print_int(self.row)) method print_col() = (print("col = "); print_int(self.col)) method print() = ( print("Shape = { "); self.print_row(); print(", "); self.print_col(); print(" }") ) } class Circle extends Shape { var radius := 1 method print_radius() = (print("radius = "); print_int(self.radius)) /* Overridden method. */ method print() = ( print("Circle = { "); self.print_row(); print(", "); self.print_col(); print(", "); self.print_radius(); print(" }") ) } /* C has static type Shape, and dynamic (exact) type Circle. */ var c : Shape := new Circle in /* Dynamic dispatch to Circle's print method. */ c.print(); /* Allowed. */ c.print_row() /* Forbidden: `print_radius' is not a member of Shape (nor of its super class(es)). */ /* c.print_radius() */ end
Methods are invariant in Tiger: each redefinition of a method in a subclass shall have the exact same signature as the original (overridden) method. This invariance applies to
let class Food {} class Grass extends Food {} class Animal { method eat(f : Food) = () } class Cow extends Animal { /* Invalid: methods shall be invariant. */ method eat(g : Grass) = () } in end
Previous: Declarations, Up: Semantics [Contents]
The ‘l-values’ (whose value can be read or changed) are: elements of arrays, fields of records, instances of classes, arguments and variables.
Some expressions have no value: procedure calls, assignments, if
s
with no else
clause, loops and break
. Empty sequences
(‘()’) and let
s with an empty body are also valueless.
The reserved word nil
refers to a value from a record
or a
class
type.
Do not use nil
where its type cannot be determined.
let type any_record = {any : int} var nil_var : any_record := nil function nil_test(parameter : any_record) : int = ... var invalid := nil /* no type, invalid */ in if nil <> nil_var then ... if nil_test(nil_var) then ... if nil = nil then ... /* no type, invalid */ end
An integer literal is a series of decimal digits (therefore it is non-negative). Since the compiler targets 32-bit architectures, since it needs to handle signed integers, a literal integer value must fit in a signed 32-bit integer. Any other integer value is a scanner error.
There is no Boolean type in Tiger: they are encoded as integers, with the same semantics as in C, i.e., 0 is the only value standing for “false”, anything else stands for “true”.
A string constant is a possibly empty series of printable characters, spaces or escapes sequences (see Lexical Specifications) enclosed between double quotes.
let var s := "\t\124\111\107\105\122\n" in print(s) end
A record instantiation must define the value of all the fields and in the same order as in the definition of the record type.
An object is created with new
. There are no constructors in
Tiger, so new
takes only one operand, the name of the type to
instantiate.
Function arguments are evaluated from the left to the right. Arrays and records arguments are passed by reference, strings and integer are passed by value.
The following example:
let type my_record = {value : int} function reference(parameter : my_record) = parameter.value := 42 function value(parameter : string) = parameter := "Tiger is the best language\n" var rec1 := my_record{value = 1} var str := "C++ rulez" in reference(rec1); print_int(rec1.value); print("\n"); value(str); print(str); print("\n") end
results in:
42 C++ rulez
Tiger Boolean operators normalize their result to 0/1. For instance,
because &
and |
can be implemented as syntactic sugar, one
could easily make ‘123 | 456’ return ‘1’ or ‘123’: make
them return ‘1’. Andrew Appel does not enforce this for ‘&’
and ‘|’; we do, so that the following program has a well defined
behavior:
print_int("0" < "9" | 42)
Arithmetic expressions only apply on integers and return integers. Available operators in Tiger are : +,-,* and /.
Comparison operators (‘=’, ‘<>’, and ‘<=’, ‘<’, ‘>=’, ‘>’) return a Boolean value.
All the comparison operators apply to pairs of strings and pairs of integers, with obvious semantics.
Comparison of strings is based on the lexicographic order.
Pairs of arrays and pairs of records of the same type can be
compared for equality (‘=’) and inequality (‘<>’). Identity
equality applies, i.e., an array or a record is only equal to itself
(shallow equality), regardless of the contents equality (deep
equality). The value nil
can be compared against a value which
type is that of a record or a class, e.g. ‘nil = nil’ is invalid.
Arrays, records and objects cannot be ordered: ‘<’, ‘>’, ‘<=’, ‘>=’ are valid only for pairs of strings or integers.
In conformance with A. Appel’s specifications, any two void entities are equal.
Assignments yield no value. The following code is syntactically correct, but type incorrect:
let var foo := 1 var bar := 1 in foo := (bar := 2) + 1 end
Note that the following code is valid:
let var void1 := () var void2 := () var void3 := () in void1 := void2 := void3 := () end
Array and record assignments are shallow, not deep, copies. Therefore aliasing effects arise: if an array or a record variable a is assigned another variable b of the same type, then changes on b will affect a and vice versa.
let type bar = {foo : int} var rec1 := bar{foo = 1} var rec2 := bar{foo = 2} in print_int(rec1.foo); print(" is the value of rec1\n"); print_int(rec2.foo); print(" is the value of rec2\n"); rec1 := rec2; rec2.foo = 42; print_int(rec1.foo); print(" is the new value of rec1\n") end
Upcasts are valid for objects because of inclusion polymorphism.
let class A {} class B extends A {} var a := new A var b := new B in a := b end
Upcasts can be performed when defining a new object variable, by forcing the type of the declared variable to a super class of the actual object.
let class C {} class D extends C {} var c : C := new D in end
Tiger doesn’t provide a downcast feature performing run time type
identification (RTTI), like C++’s dynamic_cast
.
let class E {} class F extends E {} var e : E := new F var f := new F in /* Invalid: downcast. */ f := e end
Upcast are performed when branching between two class instantiations.
Since every class inherits from Object
, you will always find
a common root.
let class A {} class B extends A {} in if 1 then new A else new B end
A sequence is a possibly empty series of expressions separated by semicolons and enclosed by parenthesis. By convention, there are no sequences of a single expression (see the following item). The sequence is evaluated from the left to the right. The value of the whole sequence is that of its last expression.
let var a := 1 in a := ( print("first exp to display\n"); print("second exp to display\n"); a := a + 1; a ) + 42; print("the last value of a is : "); print_int(a); print("\n") end
Parentheses enclosing a single expression enforce syntactic grouping.
Records and arrays have infinite lifetime: their values lasts forever even if the scope of their creation is left.
let type bar = {foo : int} var rec1 := bar{foo = 1} in rec1 := let var rec2 := bar{foo = 42} in rec2 end; print_int(rec1.foo); print("\n") end
In an if-expression:
if exp1 then exp2 else exp3
exp1 is typed as an integer, exp2 and exp3 must have
the same type which will be the type of the entire structure. The
resulting type cannot be that of nil
.
In an if-expression:
if exp1 then exp2
exp1 is typed as an integer, and exp2 must have no value. The whole expression has no value either.
In a while-expression:
while exp1 do exp2
exp1 is typed as an integer, exp2 must have no value. The whole expression has no value either.
The following for
loop
for id := exp1 to exp2 do exp3
introduces a fresh variable, id, which ranges from the value of exp1 to that of exp2, inclusive, by steps of 1. The scope of id is restricted to exp3. In particular, id cannot appear in exp1 nor exp2. The variable id cannot be assigned to. The type of both exp1 and exp2 is integer, they can range from the minimal to the maximal integer values. The body exp3 and the whole loop have no value.
A break terminates the nearest enclosing loop (while
or
for
). A break must be enclosed by a loop. A break cannot appear
inside a definition (e.g., between let
and in
), except if
it is enclosed by a loop, of course.
In the let-expression:
let decs in exps end
decs is a sequence of declaration and exps is a sequence of expressions separated by a semi-colon. The whole expression has the value of exps.
Next: Predefined Entities, Previous: Tiger Language Reference Manual, Up: Top [Contents]
Numerous extensions of the Tiger language are defined above. These extensions are not accessible to the user: if he uses one of them in a Tiger program, the compiler must reject it. They are used internally by the compiler itself, for example to desugar using concrete syntax. A special flag of the parser must be turned on to enable them.
• Additional Lexical Specifications: | New Tokens | |
• Additional Syntactic Specifications: | EBNF grammar extension | |
• Additional Semantics: | Beyond Life, the Universe and Everything |
Additional keywords and identifiers.
Used to cast an expression or a l-value to a given type.
These keywords are used to plug an existing AST into an AST being built by the parser. There is a keyword per type of pluggable AST (list of declarations, expression, l-value, type name).
They start with an underscore, and use the same letters as standard identifiers. These symbols are used internally by the compiler to name or rename entities. Note that _main is still a valid identifier, not a reserved one.
reserved-id ::= _ { letter | digit | _ }
Next: Additional Semantics, Previous: Additional Lexical Specifications, Up: Language Extensions [Contents]
In addition to the rules of the standard Tiger grammar (see Syntactic Specifications), extensions adds the following productions.
# A list of decs metavariable decs ::= _decs ( integer ) decs
exp ::= # Cast of an expression to a given type _cast ( exp , ty ) # An expression metavariable | _exp ( integer )
lvalue ::= # Cast of a l-value to a given type _cast ( lvalue , ty ) # A l-value metavariable | _lvalue ( integer )
# A type name metavariable type-id ::= _namety ( integer )
The ‘_decs’, ‘_exp’, ‘_lvalue’, ‘_namety’ keywords
are used as metavariables, i.e., they are names attached to an (already built)
AST. They don’t create new AST nodes, but are used to
retrieve existing nodes, stored previously. For instance,
upon an _exp(51)
statement, the parser fetches the tree attached
to the metavariable 51 (an expression) from the parsing context (see the
implementation for details).
Previous: Additional Syntactic Specifications, Up: Language Extensions [Contents]
A _cast
statement changes the type of an expression or an l-lvalue
to a given type. Beware that the type-checker is forced to accept the
new type as is, and must trust the programmer about the new semantics of
the expression/l-value. Bad casts can raise errors in the next stages of
the back-end, or even lead to invalid output code.
Casts work both on expressions and l-values. For instance, these are valid casts:
_cast("a", int)
_cast(a_string, int) := 42
(Although these examples could produce code with a strange behavior at execution time.)
Casts are currently only used in concrete syntax transformations inside the bounds checking extension and, as any language extension, are forbidden in standard Tiger programs.
Next: Implementation, Previous: Language Extensions, Up: Top [Contents]
These entities are predefined, i.e., they are available when you start the Tiger compiler, but a Tiger program may redefine them.
• Predefined Types: | Built-in types | |
• Predefined Functions: | Primitives |
Next: Predefined Functions, Up: Predefined Entities [Contents]
There are three predefined types:
which is the type of all the literal integers.
which is the type of all the literal strings.
which is the super class type on top of every class hierarchy (i.e., the top-most super class in the transitive closure of the generalization relationship).
Previous: Predefined Types, Up: Predefined Entities [Contents]
Some runtime function may fail if some assertions are not fulfilled. In that case, the program must exit with a properly labeled error message, and with exit code 120. The error messages must follow the standard. Any difference, in better or worse, is a failure to comply with the (this) Tiger Reference Manual.
Return the one character long string containing the character which code is code. If code does not belong to the range [0..255], raise a runtime error: ‘chr: character out of range’.
Concatenate first and second.
Exit the program with exit code status.
Flush the output buffer.
Read a character on input. Return an empty string on an end of file.
Return 1 if boolean = 0, else return 0.
Return the ascii code of the first character in string and -1 if the given string is empty.
Print string on the standard output.
Note: this is an EPITA extension. Same as print
, but the output
is written to the standard error.
Note: this is an EPITA extension. Output int in its decimal
canonical form (equivalent to ‘%d’ for printf
).
Return the size in characters of the string.
Note: this is an EPITA extension. Compare the strings a and b: return -1 if a < b, 0 if equal, and 1 otherwise.
Note: this is an EPITA extension. Return 1 if the strings a and
b are equal, 0 otherwise. Often faster than strcmp
to test
string equality.
Return a string composed of the characters of string starting at the first character (0 being the origin), and composed of length characters (i.e., up to and including the character first + length - 1).
Let size be the size of the string, the following assertions must hold:
otherwise a runtime failure is raised: ‘substring: arguments out of bounds’.
Next: The Reference Implementation, Previous: Predefined Entities, Up: Top [Contents]
• Invoking tc: | Command line options | |
• Errors: | Handling invalid input | |
• Extensions: | Making extensions to your compiler |
Next: Errors, Up: Implementation [Contents]
tc
Synopsis:
tc option… file
where file can be ‘-’, denoting the standard input.
Global options are:
Display the help message, and exit successfully.
Display the version, and exit successfully.
List the registered tasks.
Report the order in which the tasks will be run.
The options related to the file library (TC-1) are:
Prepend a directory to include path.
Append a directory to include path.
Report the include search path.
The options related to scanning and parsing (TC-1) are:
Enable Flex scanners traces.
Enable Bison parsers traces.
Parse the file given as argument (objects forbidden).
Load the definitions of the file prelude before the actual argument. The result is equivalent to parsing:
let import "prelude" in /* The argument file. */ end
To disable any prelude file, use no-prelude. The default
value is builtin
, denoting the builtin prelude.
Don’t include prelude.
The options related to the AST (TC-2) are:
Enable object constructs of the language (class and method declarations, object creation, method calls, etc.).
Same as --object --parse, i.e. parse the file given as argument, allowing objects.
Display the AST.
Reclaim the memory allocated for the AST.
The options related to escapes computation (TC-3) are:
Make sure bindings (regular or taking overloading or objects constructs into account) are computed.
Bind the name uses to their definitions (objects forbidden).
Enable the bindings display in the next --ast-display invocation. This option does not imply --bindings-compute.
Bind the name uses to their definitions, allowing objects. consistency.
The options related to the renaming to unique identifiers (TC-R) are:
Rename identifiers (objects forbidden).
The options related to escapes computation (TC-E) are:
Compute the escapes.
Enable the escape display. This option does not imply --escapes-compute, so that it is possible to check that the defaults (everybody escapes) are properly implemented. Pass -A afterward to see its result.
The options related to type checking (TC-4) are:
Make sure types (regular or taking overloading or objects constructs into account) are computed.
Compute and check (regular) types (objects forbidden).
Compute and check (regular) types, allowing objects.
The options related to desugaring (TC-D) are:
Enable the translation of for
loops into while
loops.
Enable the desugaring of string comparisons.
Make sure syntactic sugar (regular or taking overloading into account) has been removed from the AST.
Remove syntactic sugar from the AST. Desired translations must be enabled beforehand (e.g. with --desugar-for or --desugar-string-cmp).
Like --desugar but with support for overloaded functions (see TC-A).
The options related to the inlining optimization (TC-I) are:
Inline bodies of (non overloaded) functions at call sites.
Inline bodies of functions (overloaded or not) at call sites.
Remove unused (non overloaded) functions.
Remove unused functions (overloaded or not).
The options related to the bounds checking instrumentation (TC-B) are:
Add dynamic bounds checks.
Add dynamic bounds checks, with support for overloading.
The options related to overloading support (TC-A) are:
Binding variables, types, and breaks as usual, by bind function calls to the set of function definitions baring the same name.
Type-check and resolve (bind) overloaded function calls. Implies --overfun-bindings-compute.
The options related to the desugaring of object constructs (TC-O) are:
Translate object constructs from the program into their non object counterparts, i.e., transform a Tiger program into a Panther one.
The options related to the high level intermediate representation (TC-5) are:
Translate to HIR (objects forbidden). Implies --typed.
Display the high level intermediate representation. Implies --hir-compute.
The options related to the LLVM IR translation (TC-L) are:
Translate to LLVM IR.
Enable runtime displaying along with the LLVM IR.
Display the LLVM IR.
The options related to the low level intermediate representation (TC-6) are:
Trace the canonicalization of HIR to LIR.
Canonicalize the LIR fragments.
Display the canonicalized intermediate representation before basic blocks and traces computation. Implies --lir-compute. It is convenient to determine whether a failure is due to canonicalization, or traces.
Trace the basic blocks and traces canonicalization of HIR to LIR.
Compute the basic blocks from canonicalized HIR fragments. Implies --canon-compute.
Translate to LIR. Implies --traces-compute. Actually, it is nothing but a nice looking alias for the latter.
Display the low level intermediate representation. Implies --lir-compute.
The options related to the instruction selection (TC-7) are:
Convert from LIR to pseudo assembly with temporaries. Implies --lir-compute.
Display the pseudo assembly, (without the runtime prologue). Implies --inst-compute.
Display the assembly runtime prologue for the current target.
The options related to the liveness information (TC-8) are:
Save each function flow graph in a Graphviz file. Implies --inst-compute.
Save each function flow graph enriched with liveness information in a Graphviz file. Implies --inst-compute.
Save each function interference graph in a Graphviz file. Implies --inst-compute.
The options related to the target are:
Set the maximum number of callee/caller save registers to num, a positive number. Note that (currently) this does not reset the current target, hence to actually change the behavior, one needs ‘--callee-save=0 --target-mips’.
Set the target to Mips.
This optional flag sets the target to IA-32.
If no target is selected, select Mips. This option is triggered by all the options that need a target.
Report information about the current target.
The options related to the register allocation are:
Disable coalescence.
Trace register allocation.
Allocate the registers.
Display the final assembler, runtime included.
Next: Extensions, Previous: Invoking tc, Up: Implementation [Contents]
Errors must be reported on the standard error output. The exit status and the standard error output must be consistent: the exit status is 0 if and only if there is no output at all on the standard error output. There are actually some exceptions: when tracing (scanning, parsing, etc.) are enabled.
Compile errors must be reported on the standard error flow with precise error location. The format of the error output must exactly be
location: error message
where the location includes the file name, initial position, and final position. There is no fixed set of error messages.
Examples include:
$ echo "1 + + 2" | ./tc - error→standard input:1.4: syntax error, unexpected "+" error→Parsing Failed
and
$ echo "1 + () + 2" | ./tc -T - error→standard input:1.0-5: type mismatch error→ right operand type: void error→ expected type: int
Warning: The symbol error→ is not part of the actual output. It is only used in this document to highlight that the message is produced on the standard error flow. Do not include it as part of the compiler’s messages. The same applied to ⇒.
The compiler exit value should reflect faithfully the compilation status. The possible values are:
Everything is all right.
Some error which does not fall into the other categories occurred.
For instance, malloc
or fopen
failed, a file is missing
etc.
An unsupported option must cause tc
to exit 64
(EX_USAGE
) even if related to a stage option otherwise these
optional features will be tested, and it will most probably have 0. For
instance, a TC-5 delivery that does not support bounds
checking must not accept --bounds-checking.
Error detected during the scanning, e.g., invalid character.
Parse error.
Identifier binding errors such as duplicate name definition, or undefined name use.
Type checking errors (such as type incompatibility).
EX_USAGE
)The command was used incorrectly, e.g., with the wrong number of
arguments, a bad flag, a bad syntax in a parameter, or whatever. This
is the value used by argp
.
When several errors have occurred, the least value should be issued, not the earliest. For instance:
(let error in end; %)
should exit 2, not 3, although the parse error was first detected.
In addition to compiler errors, the compiled programs may have to raise a runtime error, for instance when runtime functions received improper arguments. In that case use the exit code 120, and issue a clear diagnostic. Because of the basic MIPS model we target which does not provide the standard error output, the message is to be output onto the standard output.
Previous: Errors, Up: Implementation [Contents]
A strictly compliant compiler must behave exactly as specified in this document and in Andrew Appel’s book, and as demonstrated by the samples exhibited in this document and in see (assignments)Assignments.
Nevertheless, you are entirely free to extend your compiler as you wish, as long as this extension is enabled by a non standard option. Extensions include:
Do not do that by default, in particular without checking if the output
isatty
, as the correction program will not appreciate.
If for instance you intend to support loop-expression, the construct must be rejected (as a syntax error) if the corresponding option was not specified.
In any case, if you don’t implement an extension that was suggested (such as --hir-use-ix, then you must not accept the option. If the compiler accepts an option, then the effect of this option will be checked. For instance, if your compiler accepts --hir-use-ix but does not implement it, then be sure to get 0 on these tests.
Previous: Implementation, Up: Top [Contents]
The so-called “reference compiler” is the compiler the LRDE develops to (i) prototype what students will have to implement, and to (ii) control the output from student compilers. It might be useful to some to see the name we gave to our options. The following is informative only, the exact contract for a conforming implementation of a Tiger compiler is defined above, Implementation.
$ tc --help Tiger Compiler, Copyright (C) 2004-2018 LRDE.: 0. Tasks: --task-list list registered tasks --task-graph show task graph --task-selection list tasks to be run --time-report report execution times 1. Parsing: --scan-trace trace the scanning --parse-trace trace the parse --prelude STRING name of the prelude. Defaults to "builtin" denoting the builtin prelude -X [ --no-prelude ] don't include prelude --parse parse a file --library-display display library search path -P [ --library-append ] DIR append directory DIR to the search path -p [ --library-prepend ] DIR prepend directory DIR to the search path 2. Abstract Syntax Tree: -A [ --ast-display ] display the AST --ast-dump dump the AST --tikz-style enable TikZ-style output in AST dumping 2.5 Cloning: --clone clone the Ast 3. Bind: --bound default the computation of bindings to Tiger (without objects nor overloading) -b [ --bindings-compute ] bind the identifiers -B [ --bindings-display ] enable bindings display in the AST --rename rename identifiers to unique names 3. Callgraph: --escapes-sl-compute compute the escaping static links and the functions requiring a static link --escapes-sl-display enable static links' escapes in the AST --callgraph-compute build the call graph --callgraph-dump dump the call graph --parentgraph-compute build the parent graph --parentgraph-dump dump the parent graph 3. Escapes: -e [ --escapes-compute ] compute the escaping variables and the functions requiring a static link -E [ --escapes-display ] enable escape display in the AST --escapes-check check that escape tags are correct --escapes-necessary-check check that tagged variables are escaping --escapes-sufficient-check check that escaping variables are tagged --escapes-tags-display enable escape tags display in the AST 4. Type checking: -T [ --typed ] default the type-checking to Tiger (without objects nor overloading) --types-compute check for type violations 4.5 Type checking with overloading: --overfun-bindings-compute bind the identifiers, allowing function overloading -O [ --overfun-types-compute ] check for type violations, allowing function overloading 5. Translation to High Level Intermediate Representation: --hir-compute translate to HIR -H [ --hir-display ] display the HIR --hir-naive don't use "Ix" during the translation 5.5. Translation to LLVM Intermediate Representation: --llvm-compute translate to LLVM IR --llvm-runtime-display enable runtime displayingalong with the LLVM IR --llvm-display display the LLVM IR 6. Translation to Low Level Intermediate Representation: --canon-compute canonicalize --canon-trace trace the canonicalization of the LIR -C [ --canon-display ] display the canonicalized IR --traces-compute make traces --traces-trace trace the traces computation --lir-compute translate to LIR (alias for --trace-compute) -L [ --lir-display ] display the low level intermediate representation 7. Target selection: -i [ --inst-compute ] select the instructions -R [ --runtime-display ] display the runtime --inst-debug enable instructions verbose display --rule-trace enable rule reducing display --garbage-collection enable garbage collection -I [ --inst-display ] display the instructions -Y [ --nolimips-display ] display Nolimips compatible instructions (i.e., allocate the frames and then display the instructions --targeted default the target to MIPS --target-mips select MIPS as target --target-ia32 select IA-32 as target --target-arm select ARM as target --target-display display the current target --callee-save NUM max number of callee save registers --caller-save NUM max number of caller save registers --argument NUM max number of argument registers 8. Liveness: -F [ --flowgraph-dump ] dump the flowgraphs -V [ --liveness-dump ] dump the liveness graphs -N [ --interference-dump ] dump the interference graphs 9. Register Allocation: --asm-coalesce-disable disable coalescence --asm-trace trace register allocation -s [ --asm-compute ] allocate the registers -S [ --asm-display ] display the final assembler Desugaring and bounds-checking: --desugar-for desugar `for' loops --desugar-string-cmp desugar string comparisons --desugared Default the removal of syntactic sugar from the AST to Tiger (without overloading) --desugar desugar the AST --overfun-desugar desugar the AST, allowing function overloading --raw-desugar desugar the AST without recomputing bindings nor types --bounds-checks-add add dynamic bounds checks --overfun-bounds-checks-add add dynamic bounds checks with support for overloading --raw-bounds-checks-add add bounds-checking to the AST without recomputing bindings nor types Inlining: --inline inline functions --overfun-inline inline functions with support for overloading --prune prune unused functions --overfun-prune prune unused functions with support for overloading Object: -o [ --object ] enable object extensions --object-parse parse a file, allowing objects --object-bindings-compute bind the identifiers, allowing objects --object-types-compute check for type violations, allowing objects --object-rename rename identifiers to unique names, allowing objects --object-desugar remove object constructs from the program --raw-object-desugar remove object constructs from the program without recomputing bindings nor types --overfun-object-bindings-compute bind the identifiers, allowing function overloading with object --overfun-object-types-compute check for type violations, allowing function overloading with object --overfun-object-rename rename identifiers to unique names, allowing function overloading with objects --overfun-object-desugar remove object constructs from the programallowing function overloading with objects Temporaries: --tempmap-display display the temporary table -? [ --help ] Give this help list --usage Give a short usage message --version Print program version
A super class can only be a class type, and not another kind of type.
Which is not the case in C++, where methods have covariant return values.