The Fortress Language Specification - CiteSeerX

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Several builtin generators (such as those for array indices) have an associated distribution. For these generators, sequential function simply re-distributes the underlying object as follows: sequential(r) = Sequential.distribute(r) As a convenient shorthand, the sequential function is also defined to work for distributions themselves. The complete signature for the overloadings of sequential is as follows: sequential E (g : GeneratorE) : GeneratorE sequential E (d : Distribution) : Distribution The sequential function has special meaning to the Fortress implementation; there is no need to distinguish reduction variables in loops for which generator is surrounded by a direct call to sequential . Note that at the moment there is no way to tell the compiler for performance reasons that we really mean it when we ask for sequentiality, as opposed to saying that we should preserve sequential semantics. Future versions of this specification may use the Local distribution for this purpose, or provide additional functions on generators which guarantee serial execution (rather than simply providing sequential semantics). 226
Chapter 33 Overloaded Functional Declarations Fortress allows multiple functional declarations to be in scope of a particular program point. We call this overloading. Chapter 15 describes how to determine which overloaded declarations are applicable to a particular functional call, and when several are applicable, how to select the most specific one among them. In this chapter, we give a set of restrictions on overloaded declarations that guarantee there exists a most specific declaration for any given functional call. These rules are complicated by the presence of coercion, which may enlarge the set of declarations that are applicable to a functional call, as discussed in Chapter 17. 33.1 Principles of Overloading Fortress allows multiple functional declarations of the same name to be declared in a single scope. However, recall from Chapter 7 the following shadowing rules: • dotted method declarations shadow top-level function declarations with the same name, and • dotted method declarations provided by a trait or object declaration shadow functional method declarations with the same name that are provided by a different trait or object declaration. Also, note that a trait or object declaration must not have a functional method declaration and a dotted method declaration with the same name, either directly or by inheritance. Therefore, top-level functions can overload with other top-level functions and functional methods, dotted methods with other dotted methods, and functional methods with other functional methods and top-level functions. Overloading functional declarations allows the benefits of polymorphic declarations. However, with these benefits comes the potential for ambiguous calls at run time. Fortress places restrictions on the declarations of functionals to eliminate the possibility of ambiguous call at run time, whether or not these calls actually appear in the program. Furthermore, these restrictions are checked statically. In fact, the restrictions on overloading in Fortress allow the compiler to identify the statically most specific declaration for a particular call. Therefore an implementation strategy may be used in which the statically most specific declaration is identified statically, and the runtime dispatch mechanism need only consider dispatching among that declaration plus declarations that are more specific than that declaration (proof of this is given in Section B.2). Rather than describe the overloadings that are forbidden in Fortress, this chapter outlines several criteria for valid functional overloading. At any given program point, there may be a set of overloaded declarations that are in scope. Fortress determines whether there is a possibility for ambiguous calls from this set by comparing declarations pairwise. The following three sections describe the rules to accept a pair of overloaded functional declarations. If a pair 227
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The Fortress Language Specification
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4 Evaluation 36 4.1 Values . . . .
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12 Functions 85 12.1 Function Decla
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17.7 Coercions for Tuple and Arrow
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IV Fortress for Library Writers 214
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40.10The Trait Fortress.Core.Binary
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Chapter 1 Introduction The Fortress
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A note on the presented libraries i
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component HelloWorld export Executa
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foo:String → () baz: String → S
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fortress upgrade Gary with Ralph No
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halve(x : R64) : R64 = x/2 Predicta
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while x < 10 do print x x += 1 end
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It is also possible to convert a me
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factorial(n) = ∏ i←1:n i This f
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In both methods cons and append , t
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default distributions will provide
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Chapter 3 Programs A program consis
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Chapter 10), a literal (see Section
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(discussed in Section 13.13) to a s
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Chapter 5 Lexical Structure A Fortr
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U+0021 EXCLAMATION MARK ! U+0023 NU
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If a character (or any other syntac
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BIG SI unit absorbs abstract also a
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escape sequences are useful for ASC
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5.14.1 Multicharacter Enclosing Ope
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Note: the elegant way to write Avog
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• top-level variable declarations
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declares id to be a mutable variabl
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several new variables. This syntax
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Chapter 7 Names Names are used to r
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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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Page 177 and 178: Fortress.IO Fortress.Crypto Fortres
Page 179 and 180: Part III Fortress APIs and Document
Page 181 and 182: 23.1.3 hash(maxval: N64): N64 23.1.
Page 183 and 184: opr =(self,other: Boolean):Boolean
Page 185 and 186: 24.1.20 getter hashCode(): N64 24.1
Page 187 and 188: False: BooleanInterval Uncertain: B
Page 189 and 190: 24.2.11 opr ∧(self,other: Boolean
Page 191 and 192: 24.2.19 possibly(self): Boolean 24.
Page 193 and 194: Chapter 25 Numbers 25.1 Rational Nu
Page 195 and 196: opr ⌈self ⌉: N realpart(self):
Page 197 and 198: 25.1.11 opr (self,other: Q):Boolean
Page 199 and 200: 25.1.26 floor(self): Z 25.1.27 opr
Page 201 and 202: Chapter 26 Negated Relational Opera
Page 203 and 204: 26.1.26 opr ⊀T extends BinaryPred
Page 205 and 206: 27.3 The Trait Fortress.Standard.Un
Page 207 and 208: Chapter 29 Dimensions and Units 29.
Page 209 and 210: unit secondOfAngle secondsOfAngle:
Page 211 and 212: Chapter 30 Tests 30.1 The Object Fo
Page 213 and 214: 31.2 Convenience Types An optional
Page 215 and 216: Chapter 32 Parallelism and Locality
Page 217 and 218: y evaluating the two elements of th
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Page 221 and 222: v = spawn at a.region(i) do a i end
Page 223 and 224: expr ∑ type wrapper ∑ body R,
Page 225: 32.8.3 Using Overloading to Adapt G
Page 229 and 230: coercions: T U ⇐⇒ T ♦ U ∧
Page 231 and 232: The More Specific Rule for Function
Page 233 and 234: An infix/multifix operator declarat
Page 235 and 236: may be so defined except ordinary p
Page 237 and 238: and here some of these computed dim
Page 239 and 240: unit name 1 name 2 name 3 : . . . u
Page 241 and 242: Chapter 36 Support for Domain-Speci
Page 243 and 244: Because syntax expanders are define
Page 245 and 246: Part V Fortress APIs and Documentat
Page 247 and 248: property ∀(a:T) ¬(a ∼ a) end A
Page 249 and 250: trait PartialOrderOperatorsT extend
Page 251 and 252: The HasMinimalElement trait specifi
Page 253 and 254: The trait Commutative requires the
Page 255 and 256: A value e is a left identity for a
Page 257 and 258: trait ApproximatelyHasInverses T ex
Page 259 and 260: end extends { ApproximateCommutativ
Page 261 and 262: A default definition is provided fo
Page 263 and 264: trait RationalQuantityunit U absorb
Page 265 and 266: (self,other:RationalQuantityU,ninf
Page 267 and 268: 38.2.4 getter hashCode(): Z64 38.2.
Page 269 and 270: Chapter 39 Components and APIs We d
Page 271 and 272: Chapter 40 Memory Sequences and Bin
Page 273 and 274: updatenat k(j: IntegerStatick, v: T
Page 275 and 276: 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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