The Fortress Language Specification - CiteSeerX

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The requirement of APIs being imported or exported whenever an API using them is exported also applies to visible APIs. Thus, if we hide an API used by another exported API, we must hide that other API as well. Link With constrained APIs, there is a new restriction on link: Any API visible in one constituent and imported by another must be exported by some constituent. This restriction is necessary because an API visible in a component cannot be imported by that component. Thus, if one of the component’s constituents imports that API, then the API must be provided by some other constituent. Other than that, the link operation is largely unchanged: the visible APIs are just all the APIs visible in any constituent, and the provided APIs are just those exported by any constituent. There is a subtle additional restriction on how linked components can be upgraded, which we discuss below. Rather than requiring users and developers to call constrain and hide directly, we provide optional parameters to the link operation to do these operations immediately. The link operation has the following type: link(result:String, constituents:String..., exports = {}, hide = {}):() If the exports clause is present, only those APIs listed in the set following exports are exported; the others are constrained. If the hide clause is present, those APIs listed in the set following hide are hidden. An exception is thrown if the exports clause contains any API not exported by any constituent, or if the hide clause contains any API not visible in any constituent. Hiding enables us to handle the rare case in which programmers want to link multiple components that implement the same API without upgrading them to use the same implementation. Before linking, the programmer simply hides (or constrains) the API in every component that exports it except the one that should provide the implementation for the new compound component. For example, suppose we wish to link the following two components: • A component NetApp that imports Fortress.IO and exports the Fortress.Net API. • A component EditApp that imports Fortress.IO and exports the Fortress.Swing.Textrf API. We want to link these two components to use in building an application for editing messages and sending them over a network. But we want to use different implementations of Fortress.IO (e.g., IOApp1 and IOApp2 for the two components). We simply perform the following operations: link(temp1, NetApp, IOApp1, exports = {Fortress.Net}, hide = {Fortress.IO}) link(temp2, EditApp,IOApp2, exports = {Fortress.Swing.Textrf}, hide = {Fortress.IO}) link(NetEdit, temp1, temp2) In this case, the NetEdit component does not export, or even make visible, Fortress.IO at all. Upgrade For the upgrade operation, there is no change at all in the semantics. However, because hiding and constraining APIs allow us to change the APIs exported by a component, it is possible to do some upgrades that are not possible without these operations. For example, suppose we have a component IOSecurity that exports Fortress.IO and Fortress.Security, and we want to upgrade CoolCryptoApp with IOSecurity. As discussed above, we cannot use IOSecurity directly because IronLink exports Fortress.IO but not Fortress.Security. We can get around this restriction by doing two upgrades, one with Fortress.Security hidden and the other with Fortress.IO hidden. hide(IOSecurity, NewIO, Fortress.Security) hide(IOSecurity, NewSecurity, Fortress.IO) upgrade(CoolCryptoApp, NewSecurity, temp1) upgrade(CoolCryptoApp.3.0, temp1, NewIO) The resulting component is shown in Figure 22.5. 176
Fortress.IO Fortress.Crypto Fortress.Security CoolCryptoApp.3.0 Fortress.IO Fortress.Crypto Fortress.Security NewSecurity Fortress.IO Fortress.Security IronLink − upgrade NewIO Fortress.IO Fortress.IO Fortress.Security Fortress.Crypto IronCrypto IOSecurity IOSecurity Fortress.IO Fortress.Security Fortress.Security Figure 22.5: Upgrading with hidden APIs: Crossed out APIs are hidden. 177
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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
Page 125 and 126: Chapter 16 Operators Operators are
Page 127 and 128: • “ordinary” operators: + −
Page 129 and 130: left context whitespace operator fi
Page 131 and 132: The rules below are designed to for
Page 133 and 134: 16.8.3 Enclosing Operators When use
Page 135 and 136: 16.8.9 Intersection, Union, and Set
Page 137 and 138: Chapter 17 Conversions and Coercion
Page 139 and 140: 17.3 Coercion Invocations One may i
Page 141 and 142: arguments nor with variable number
Page 143 and 144: trait B extends A end trait C exten
Page 145 and 146: a new coercion in a subexpression
Page 147 and 148: for tokens. For readability, plural
Page 149 and 150: Chapter 19 Tests and Properties For
Page 151 and 152: 19.5 Test Suites In order to allow
Page 153 and 154: Chapter 20 Type Inference Type infe
Page 155 and 156: 3. If a i is a functional applicati
Page 157 and 158: 21.2 Programming Discipline If Fort
Page 159 and 160: Here the call f(a, a) ends up setti
Page 161 and 162: 2. Ancestors, dynamically ordered b
Page 163 and 164: The ways in which fortresses are ac
Page 165 and 166: Component equivalence is determined
Page 167 and 168: 22.5 Type Inference for Components
Page 169 and 170: Fortress.IO Fortress.Crypto IronLin
Page 171 and 172: execute(componentName:String, args:
Page 173 and 174: 3. If the replacement does not expo
Page 175: This method runs all test functions
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
Page 219 and 220: There is a DefaultDistribution whic
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Page 225 and 226: 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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