The Fortress Language Specification - CiteSeerX

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sun = Sol planets = { Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto } position = Polar(25000 lightYears, 0 radians) ω : R64 AngularVelocity = 2π radians / 226 million yearsin seconds variation(ω ∆ ) = ω += ω ∆ end In this example, the object SolarSystem extends the traits StarSystem and OrbitingObject. The fields ω and position are defined with appropriate quantities. The field sun is defined to be another object named Sol, and the field planets is defined to be a set of objects. The method variation is defined to take a single parameter ω ∆ , and update the ω field of the object. As this example illustrates, Fortress provides static checking of physical units and dimensions on quantities. Note that the identifiers used in this example are not restricted to ASCII character sequences. Fortress allows the use of Unicode characters in program identifiers, as well as subscripts and superscripts. (See Appendix E for a discussion of Unicode and support for entering programs in ASCII.) Fortress also allows multiplication to be expressed by simple juxtaposition, as can be seen in the definitions of ω and position . Fortress also allows for operator overloading, as well as a facility for extending the syntax with domain-specific languages. Although Fortress is statically and nominally typed, types are not specified for all fields, nor for all method parameters and return values. Instead, wherever possible, type inference is used to reconstruct types. In the examples throughout this specification, we often omit the types when they are clear from context. Additionally, types can be parametric with respect to other types and values (most notably natural numbers). These design decisions are motivated in part by our goal of making the scientist/programmer’s life as easy as possible without compromising good software engineering. In particular, they allow us to write Fortress programs that preserve the look of standard mathematical notation. In addition to objects and traits, Fortress allows the programmer to define top-level functions. Functions are first-class values: They can be passed to and returned from functions, and assigned as values to fields and variables. Functions and methods can be overloaded, with calls to overloading methods resolved by multiple dynamic dispatch similarly to the manner described in [17]. Keyword parameters and variable size argument lists are also supported. Fortress programs are organized into components, which export and import APIs and can be linked together. APIs describe the “shape” of a component, specifying the types in traits, objects and functions provided by a component. All external references within a component (i.e., references to traits, objects and functions implemented by other components) are to APIs imported by the component. We discuss components and APIs in detail in Chapter 22. To address the needs of modern high-performance computation, Fortress also supports a rich set of operations for defining parallel execution and distribution of large data structures. This support is built into the core of the language. For example, for loops in Fortress are parallel by default. 1.2 Organization This language specification is organized as follows. In Part II, the Fortress language features for application programmers are explained, including objects, types, and functions. Relevant parts of the concrete syntax are provided with many examples. The full concrete syntax of Fortress is described in Appendix G. In Part III, APIs and documentation of some of the Fortress standard libraries for application programmers are presented. Part IV describes advanced Fortress language features for library writers and Part V presents APIs and documentation for some of the Fortress standard libraries for library writers. Finally, in Part VI, the Fortress calculi, support for Unicode characters, and the Fortress grammars are described. 14
A note on the presented libraries in Parts III and V: The Fortress standard libraries presented in this draft specification should not be construed as exhaustive or complete. Presentation of additional libraries is planned for future drafts, as are modifications to the libraries included here. 15
Page 1 and 2: The Fortress Language Specification
Page 3 and 4: 4 Evaluation 36 4.1 Values . . . .
Page 5 and 6: 12 Functions 85 12.1 Function Decla
Page 7 and 8: 17.7 Coercions for Tuple and Arrow
Page 9 and 10: IV Fortress for Library Writers 214
Page 11 and 12: 40.10The Trait Fortress.Core.Binary
Page 13: Chapter 1 Introduction The Fortress
Page 17 and 18: component HelloWorld export Executa
Page 19 and 20: foo:String → () baz: String → S
Page 21 and 22: fortress upgrade Gary with Ralph No
Page 23 and 24: halve(x : R64) : R64 = x/2 Predicta
Page 25 and 26: while x < 10 do print x x += 1 end
Page 27 and 28: It is also possible to convert a me
Page 29 and 30: factorial(n) = ∏ i←1:n i This f
Page 31 and 32: In both methods cons and append , t
Page 33 and 34: default distributions will provide
Page 35 and 36: Chapter 3 Programs A program consis
Page 37 and 38: Chapter 10), a literal (see Section
Page 39 and 40: (discussed in Section 13.13) to a s
Page 41 and 42: Chapter 5 Lexical Structure A Fortr
Page 43 and 44: U+0021 EXCLAMATION MARK ! U+0023 NU
Page 45 and 46: If a character (or any other syntac
Page 47 and 48: BIG SI unit absorbs abstract also a
Page 49 and 50: escape sequences are useful for ASC
Page 51 and 52: 5.14.1 Multicharacter Enclosing Ope
Page 53 and 54: Note: the elegant way to write Avog
Page 55 and 56: • top-level variable declarations
Page 57 and 58: declares id to be a mutable variabl
Page 59 and 60: several new variables. This syntax
Page 61 and 62: Chapter 7 Names Names are used to r
Page 63 and 64: 7.3 Qualified Names Fortress provid
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Fortress also allows coercion betwe
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• element types of a tuple type c
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TypeAlias ::= type Id [StaticParams
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‘}’. If such a clause contains
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Note that a trait declaration inher
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the parametric trait WrappedDiction
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Chapter 10 Objects An object is a v
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FldDef ::= FldMod ∗ Id [IsType] (
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Chapter 11 Static Parameters Trait,
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11.5 Operator and Identifier Parame
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Chapter 12 Functions Functions are
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swap(x :Object, y : Object) = (y, x
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A function declaration may be separ
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Chapter 13 Expressions Fortress is
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Negating the literal 0 produces a s
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the function is evaluated with the
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13.10 Assignments Syntax: Expr ::=
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treeSum(t : TreeLeaf) = 0 treeSum(t
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Several common mathematical operato
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The body of each iteration is run i
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to the value of the condition expre
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An atomic expression consists of th
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13.26 Try Expressions Syntax: Flow
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13.27.2 Static Expressions and Valu
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A = [1 2 3; 4 5 6; 7 8 9] then A 1,
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evaluates to the set {0, 4, 16} Map
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ignore(f x) is equivalent to: f x;
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trait CheckedException extends { Ex
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Chapter 15 Overloading and Multiple
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e called with. In other words, we e
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Chapter 16 Operators Operators are
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• “ordinary” operators: + −
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left context whitespace operator fi
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The rules below are designed to for
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16.8.3 Enclosing Operators When use
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16.8.9 Intersection, Union, and Set
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Chapter 17 Conversions and Coercion
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17.3 Coercion Invocations One may i
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arguments nor with variable number
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trait B extends A end trait C exten
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a new coercion in a subexpression
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for tokens. For readability, plural
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Chapter 19 Tests and Properties For
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19.5 Test Suites In order to allow
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Chapter 20 Type Inference Type infe
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3. If a i is a functional applicati
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21.2 Programming Discipline If Fort
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Here the call f(a, a) ends up setti
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2. Ancestors, dynamically ordered b
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The ways in which fortresses are ac
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Component equivalence is determined
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22.5 Type Inference for Components
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Fortress.IO Fortress.Crypto IronLin
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execute(componentName:String, args:
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3. If the replacement does not expo
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This method runs all test functions
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Fortress.IO Fortress.Crypto Fortres
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Part III Fortress APIs and Document
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23.1.3 hash(maxval: N64): N64 23.1.
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opr =(self,other: Boolean):Boolean
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24.1.20 getter hashCode(): N64 24.1
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False: BooleanInterval Uncertain: B
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24.2.11 opr ∧(self,other: Boolean
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24.2.19 possibly(self): Boolean 24.
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Chapter 25 Numbers 25.1 Rational Nu
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opr ⌈self ⌉: N realpart(self):
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25.1.11 opr (self,other: Q):Boolean
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25.1.26 floor(self): Z 25.1.27 opr
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Chapter 26 Negated Relational Opera
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26.1.26 opr ⊀T extends BinaryPred
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27.3 The Trait Fortress.Standard.Un
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Chapter 29 Dimensions and Units 29.
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unit secondOfAngle secondsOfAngle:
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Chapter 30 Tests 30.1 The Object Fo
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31.2 Convenience Types An optional
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Chapter 32 Parallelism and Locality
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y evaluating the two elements of th
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There is a DefaultDistribution whic
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v = spawn at a.region(i) do a i end
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expr ∑ type wrapper ∑ body R,
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32.8.3 Using Overloading to Adapt G
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Chapter 33 Overloaded Functional De
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coercions: T U ⇐⇒ T ♦ U ∧
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The More Specific Rule for Function
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An infix/multifix operator declarat
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may be so defined except ordinary p
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and here some of these computed dim
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unit name 1 name 2 name 3 : . . . u
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Chapter 36 Support for Domain-Speci
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Because syntax expanders are define
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Part V Fortress APIs and Documentat
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property ∀(a:T) ¬(a ∼ a) end A
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trait PartialOrderOperatorsT extend
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The HasMinimalElement trait specifi
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The trait Commutative requires the
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A value e is a left identity for a
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trait ApproximatelyHasInverses T ex
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end extends { ApproximateCommutativ
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A default definition is provided fo
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trait RationalQuantityunit U absorb
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(self,other:RationalQuantityU,ninf
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38.2.4 getter hashCode(): Z64 38.2.
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Chapter 39 Components and APIs We d
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Chapter 40 Memory Sequences and Bin
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updatenat k(j: IntegerStatick, v: T
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40.1.12 update(j:IndexInt, v: T): L
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40.3.2 opr nat m[r:RangeOfStaticSiz
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40.5 The Trait Fortress.Core.Binary
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40.5.5 bit(m:IndexInt): Bit The res
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40.6 The Trait Fortress.Core.Binary
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40.6.4 opr nat m[r:RangeOfStaticSiz
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40.6.16 opr ‖ nat m,bool bigEndia
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countLeadingZeroBits():IndexInt cou
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40.7.41 signedShift(j:IndexInt):T 4
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40.8.6 signedDivide(other: T,overfl
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littleEndian():BinaryEndianLinearEn
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40.9.16 opr ‖ nat m,nat radix,nat
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v: BinaryEndianWordb,bigEndianBytes
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40.10.9 opr nat m[r:RangeOfStaticSi
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40.10.24 splitnat b ′ () : Binary
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itAnd(selfStart: IndexInt,source:T,
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40.13.2 wrappingAdd(selfStart: Inde
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40.13.30 unsignedMax(selfStart: Ind
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40.13.55 gatherBits(selfStart:Index
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Appendix A Fortress Calculi A.1 Bas
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Values, evaluation contexts, redexe
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Expression typing: p; ∆; Γ ⊢ e
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α, β type variables f method name
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Function/method name lookup: Fname(
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One owner for all the visible metho
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Traits defining a method: defining
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Values, evaluation contexts, and re
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Valid function declarations: p ⊢
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Method definition lookup: visible p
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Values, intermediate expressions, e
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Field typing: p; ∆; Γ ⊢ vd ok
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Appendix B Overloaded Functional De
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Proof. We prove this for δ, but th
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Upgrade A predicate upg? takes two
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a is rendered as a foobar is render
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• If a portion is sub and another
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supercalifragilisticexpialidocious
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any alternative names, with undersc
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Appendix F Operator Precedence, Cha
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U+007C VERTICAL LINE | | U+2016 DOU
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The following two operators have th
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U+003D EQUALS SIGN = = EQ U+2243 AS
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U+22DD EQUAL TO OR GREATER-THAN U+2
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U+2289 NEITHER A SUPERSET OF NOR EQ
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F.4.8 Miscellaneous Relational Oper
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U+21A5 UPWARDS ARROW FROM BAR U+21A
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U+2224 DOES NOT DIVIDE ∤ U+2225 P
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U+27F8 LONG LEFTWARDS DOUBLE ARROW
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U+2960 UPWARDS HARPOON WITH BARB LE
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U+29ED BLACK CIRCLE WITH DOWN ARROW
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Appendix G Concrete Syntax In this
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Extends ::= extends TraitTypes Excl
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StaticParam ::= Id [Extends] [absor
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Value ::= Literal | fn ValParam [Is
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Appendix H Generated Concrete Synta
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-> fn_decl -> object_decl -> var_de
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-> id extends_opt absorbs_opt -> "n
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-> w "excludes" w type_ref_list com
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-> obj_decl_body_elem br obj_decl_b
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-> op wr op_follows_op_w -> op wr e
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-> no_space_op_expr_result no_space
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id_opt -> -> w id with_opt -> -> w
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-> unpasting_elem rect_separator un
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-> "}" comprehension -> set_compreh
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-> do_expr -> for_expr -> spawn_exp
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-> type_ref -> "(" w type_ref w ","
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enc -> enc_literal op_or_enc -> op
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Bibliography [1] O. Agesen, L. Bak,
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