Imperative vs functional languages ( continued ) electrical engineering Computers their outputs to memory frequency measured in Hz, KHz, MHz, GHz…) Compiler Construction 22 / 193 ▶ Computer science is the illegitimate child of mathematics and ▶ Electrical engineering gave us the hardware , the actual machine ▶ Nearly all ideas come from mathematics ▶ Digital electronics: Gates, fmip-fmops, latches, memory, etc ▶ Boolean functions that read their inputs from memory & write ▶ Reading & writing are synchronized using a clock (with a ▶ A fjnite-state machine Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) level of digital electronics computation Compiler Construction 23 / 193 ▶ We cannot design large software systems while thinking at the ▶ We need some theoretical foundations for programming & Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) What is mathematics? expressed in this language What computer science takes from mathematics? In short: Everything! Compiler Construction 24 / 193 ▶ A language ▶ A set of ideas, notions, defjnitions, techniques, results, all ▶ Programming is based on a computable mathematics ▶ Theoretical computer science uses all of mathematics Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) What programming languages take from mathematics? numbers, types, sets, ordered n tuples, structures, etc tuples, sets, etc), abstraction, mapping, folding, etc. Nearly all of the ideas in computer science come from mathematics! Compiler Construction 25 / 193 ▶ A language ▶ Notions such as functions, variables, expressions, evaluation, ▶ Operations such as arithmetic, Boolean, structural (e.g., on n Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Mathematical objects are free of the limitations that beset computers: Real-world compromises physical computer: Compiler Construction 26 / 193 ▶ Computers can only approximate real numbers ▶ Computers cannot implement infjnite tape (Turing machines) ▶ Mathematical objects are cheaper than objects created on a ▶ Functions are mappings; They take no time! ▶ Knowing that an object exists is often all we need! ▶ Bad things cannot happen: ▶ No exceptions, errors, incorrect results ▶ Nothing is lost, nothing is “too big” or “too much” Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Functional programming languages Imperative programming languages Compiler Construction 27 / 193 ▶ Closer to mathematics ▶ Easier to reason about ▶ Easier to transform ▶ Easier to generate automatically ▶ Farther from mathematics ▶ Harder to reason about ▶ Harder to transform ▶ Harder to generate automatically Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Example of non-mathematical ideas: Side efgects Compiler Construction string string -> int that returns the number of characters in the 28 / 193 (rather than char * ) Imagine having to teach C programming to a logician ▶ To simplify matters, let’s pretend there is a string type in C ▶ You teach them a simplifjed version of printf : ▶ Only takes a single string argument ▶ Returns an int : the number of characters in the string ▶ Roughly: printf : string -> int ▶ But the logician objects: He already knows of a function from ▶ strlen : string -> int ▶ He wants to know the difgerence between printf and strlen Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Side efgects: The Dialogue the screen & also returns the number of characters it printed!” right?” printf !” Compiler Construction 29 / 193 ▶ You: “Simple, printf also prints the string to the screen!” ▶ Logician: “What does it mean to print??” ▶ You: “Seriously?? The printf function prints its argument to ▶ Logician: “But you said the domain of printf is string -> int , ▶ You: “Yes, so?” ▶ Logician: “Then where’s the screen??” ▶ You: “In front of you!” ▶ Logician: “Where’s the screen in the domain of the function Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Side efgects: The Dialogue ( continued ) global variable.” be a variable when it’s not passed as a parameter, and its type is not expressed in the domain of the function??” efgect: It is not expressed in the type!” domain of printf all wrong!” Compiler Construction 30 / 193 ▶ You: “It isn’t in the domain. You can think of the screen as a ▶ Logician: “I have no idea what you mean: How can the screen ▶ You: “But that’s the whole point of this printing being a side ▶ Logician: “Well, then printf isn’t a function!” ▶ You: “Ummm…” ▶ Logician (having a Eureka!-moment): “I get it now! You got the Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Side efgects from a logical point of view Compiler Construction been mapped into another screen in the range. the function call an illusion of change, as if the environment has changed: An 31 / 193 written explicitly in the original type given for printf ▶ The real type of printf is string × screen → int × screen ▶ The underlined parts of the type are implicit, i.e., they are not ▶ The implicit parts of the type form the environment ▶ The function call mentions only the explicit arguments ▶ Leaving out the implicit arguments in the function call creates illusory notion of time has been created; We have the environment before the function call, and the environment after ▶ In fact, nothing has changed: The screen in the domain has Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Side efgects from a logical point of view ( continued ) { printf("Hello "); printf("world!\n"); } screen object in the domain of printf("world!\n"); “ordering” matters! Compiler Construction 32 / 193 ▶ Introducing side efgects introduces discrete time ▶ Having introduced time, we must now introduce sequencing: ▶ The notion of sequencing is, like time, illusory: ▶ The screen object in the range of printf("Hello "); is the ▶ So the two printf expressions are nested, and this is why their Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Imperative C Compiler Construction printf to printf 33 / 193 Functional Rendition } printf("World!\n"); printf("Hello "); { ⟨ "Hello " , screen ⟩ = ⇒ ⟨ 6 , screen ⊕ "Hello " ⟩ ⟨ "World!\n" , screen ⊕ "Hello " ⟩ = ⇒ ⟨ 7 , screen ⊕ "Hello World\n" ⟩ ▶ The return value of the second call ▶ The screen after the second call to Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Functional programming languages computation they are used to implement it on a real computer!) Compiler Construction 34 / 193 ▶ Closer to the mathematical notions of function, variable, ▶ Nothing is implicit ▶ Easier to reason about ▶ Side efgects are not an explicit part of the language (although ▶ Ofgers many other advantages Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Imperative programming languages variable, evaluation convenience) sequences, environment, etc., that require translation before we can reason about them various parts of a software system, making it harder to debug Compiler Construction 35 / 193 ▶ Farther away from the mathematical notions such as function, ▶ Hides information through the use of implicit arguments (for ▶ Harder to reason about: Contains notions such as side efgects, ▶ Abstraction is harder, prone to errors ▶ Side efgects create implicit, knotty inter-dependencies between Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Abstraction in functional programming languages etc Abstraction in imperative programming languages command in Latin) Compiler Construction 36 / 193 ▶ Values ⇒ Expressions ⇒ Functions ▶ Higher-order functions ▶ Mathematical operators: mapping, folding, fjltering, partitioning, ▶ The interpreter evaluates expressions ▶ State ⇒ Change ⇒ Commands ⇒ Procedures ▶ Object-oriented programming ▶ Imperative ≡ Based upon commands ( imperare means to ▶ The interpreter performs commands Mayer Goldberg \ Ben-Gurion University
Programming paradigms: A reality check in which side-efgects cannot be expressed impossible to use side-efgects, but they don’t make these easy or fun to use functional languages Compiler Construction 37 / 193 ▶ There are very few strictly functional languages, i.e., languages ▶ Most languages are quasi-functional: They don’t make it ▶ Most new imperative languages do include features from ▶ anonymous functions (“lambda”) ▶ higher-order functions ▶ modules/namespaces/functors Mayer Goldberg \ Ben-Gurion University
Imperative vs functional languages ( continued ) Question Languages based on the functional paradigm — Compiler Construction 38 / 193 👏 do not allow us to perform side efgects 👏 do not support object-oriented programming 👏 are not suited to model and solve “real” problems 👏 are slow and ineffjcient 👎 support high order functions Mayer Goldberg \ Ben-Gurion University
Further Reading http://blog.jenkster.com/2015/12/what-is-functional-programming.html , or Compiler Construction 39 / 193 🔘 Comparing programming paradigms 🔘 What is functional programming at Mayer Goldberg \ Ben-Gurion University
Interpreters evaluate/perform Introduction to compiler construction The functional picture (evaluate) Compiler Construction 40 / 193 ▶ L 1 : Language ▶ L 2 : Language ▶ P L : A program in language L ▶ Values: A set of values ▶ � · � : Semantic brackets ▶ An interpreter is a function Int L : L → Values ▶ Interpreters map expressions to their values ▶ For example: In functional Scheme, we have Int Scheme � (+ 3 5) � = 8 Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Interpreters evaluate/perform Compiler Construction created: “Something changed in the environment” environment in the range, an illusion of change has been 41 / 193 environment to the product of a value and an environment The imperative picture (perform) ▶ An interpreter is a function Int L : L × Environment → Values × Environment ▶ Interpreters map the product of an expression and an ▶ The environments are implicit in the imperative language ▶ When the environment in the domain is not equal to the ▶ For example: In imperative Scheme, we have Int Scheme � ⟨ ( defjne x 3) , { x �→ undefjned }⟩ � = ⟨ # ⟨ void ⟩ , { x �→ 3 }⟩ Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Compilers translate interpreters for both the source and target language: Compiler Construction 42 / 193 L 1 : L 1 → L 2 ▶ A compiler is a function Comp L 2 ▶ Compilers translate programs from one language to another ▶ Let P L 1 ∈ L 1 , then Comp L 2 L 1 � P L 1 � ∈ L 2 ▶ The correctness of the translation is established using Int L 1 � P L 1 � = Int L 2 � Comp L 2 L 1 � P L 1 �� Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Compilers translate ( continued ) Compiler Construction 43 / 193 ▶ We may chain any number of compilers together: Int L 1 � P L 1 � = Int L 2 � Comp L 2 L 1 � P L 1 �� = Int L 3 � Comp L 3 L 2 � Comp L 2 L 1 � P L 1 ��� = Int L 4 � Comp L 4 L 3 � Comp L 3 L 2 � Comp L 2 L 1 � P L 1 ���� = . . . etc. Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Question Compiled code is generally faster than interpreted code. So why do we need interpreters? Why not stick with compiled code? Compiler Construction 44 / 193 👏 It’s easier to program in interpreted languages 👏 It’s easier to debug interpreted code 👏 Interpreters are more fmexible than compilers 👏 The difgerence is pretty much a matter of personal taste 👎 Interpreters are the only way to reach values Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Question When we program directly in machine language, where’s the interpreter? underlying interpretation interpreter for the given micro-architecture Compiler Construction 45 / 193 👏 The operating system is the interpreter 👏 The shell is the interpreter 👏 There is no interpreter 👏 The process of translating code to machine language is the 👎 The microprocessor is a hardware implementation of an Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Question If interpreters are a logical necessity, why do we need a compiler? Compiler Construction 46 / 193 👏 For generality 👏 For ease 👏 For fmexibility 👏 For portability 👎 For optimizations Mayer Goldberg \ Ben-Gurion University
Introduction to compiler construction Another way of looking at the question A compiler from language L to language L (itself!) is… …just an optimizer! Compiler Construction 47 / 193 Mayer Goldberg \ Ben-Gurion University
What is an optimization More effjcient code Compiler Construction or any other resource consumed by the code A compiler optimization is a semantics-preserving transformation that Resources include: 48 / 193 interpretation results in more effjcient code Semantics-preserving ( ≡ meaning-preserving) ▶ Returns the same value (as the original code) under ▶ The interpreter takes less resources to evaluate the code. ☞ Execution time ▶ Computer memory ▶ Network traffjc ▶ Microprocessor registers Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) Special-purpose compilers may optimize for non-standard “resources”: motion crossovers of edges “widows”, “orphans”, hyphenations, and other typographically problematic conditions Compiler Construction 49 / 193 ▶ Compilers to g-code , a language for CNCs, will try to minimize ▶ Compilers of graphs to visual presentations will try to minimize ▶ Compilers of document-layout languages will try to minimize Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) Question Why do programmers write less-than-optimized code? What is the rationale for having compilers be in charge of optimizations? Are All these reasons are true, but irrelevant! intentionally write less-effjcient code? Compiler Construction 50 / 193 good programmers really that rare?? ▶ Good code is hard to write ▶ Some programmers are incompetent ▶ Compilers are faster at detecting opportunities for optimizations ▶ Consistent output: Once debugged, compilers make no mistakes ☞ Can you envision a reason why a programmer might Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) Which code is better: Code I for (i = 0; i < 200; ++i) { A[i] = 0; } for (i = 0; i < 200; ++i) { B[i] = 0; } Code II for (i = 0; i < 200; ++i) { A[i] = 0; B[i] = 0; } Code III #define M 200 #define N 200 ... for (i = 0; i < M; ++i) { A[i] = 0; } for (i = 0; i < N; ++i) { B[i] = 0; } Compiler Construction 51 / 193 Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) Analysis Compiler Construction 52 / 193 ▶ Code I ▶ less general than Code III ▶ less effjcient than Code II ▶ less maintainable than Code III ▶ Code II ▶ less general than Code I ▶ more effjcient than Code I, Code III ▶ less maintainable than Code I ▶ Code III ▶ more general than Code I, Code II ▶ less effjcient than Code II ▶ more maintainable than Code I, Code II Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) So which code is better? FACT: Optimizing the loops in Code III, converting it to Code II, is performed by most compilers today Conclusion People write less-than-optimal code because: Compiler Construction 53 / 193 ▶ Clearly Code III is better! ▶ It is more general ▶ It is more maintainable ▶ It is more fmexible ▶ Most compilers optimize away such ineffjciency Mayer Goldberg \ Ben-Gurion University
What is an optimization ( continued ) How people use compilers Compiler Construction obtain effjcient code. unmaintainable, overly-specifjc, machine-dependent code in order to Without optimizing compilers, we would be forced to write 54 / 193 effjciency: ▶ Want to program in a more general, maintainable, fmexible way ▶ Compilation is a point-in-time where generality is traded for ▶ Compilers are opportunistic ▶ Compilers identify opportunities to trade generality for effjciency ▶ The resulting code is unreadable, unmaintainable, machine-specifjc, and fast ▶ We [normally] don’t touch the compiled code: For programmers, the quality of only the source code matters Mayer Goldberg \ Ben-Gurion University
Composing & combining processors, interpreters, compilers, & programs Compiler Construction for you! We have 5 new blocks Remember Lego? languages!) into equivalent programs written in in language L programs written in language L We can compose 55 / 193 ▶ Processors running programs written ▶ Interpreters written in L ′ , running ▶ Compilers written in L ′ , running on L , compile programs written in L ′′ L ′′′ (we are talking about 4 ▶ Programs written in L ′ , running on L Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, compilers, & programs A processor interpreters for some language The languages they provide What it looks like Compiler Construction 56 / 193 provides ▶ Hardware-implementations of lang processor ▶ They have only 1 docking point: Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, source language and compiled to Compiler Construction compilers, & programs additional docking point compiler. Such programs have an some other language using a What it looks like these days point: The language they run on A program 57 / 193 binary. This is hardly ever done hand-written directly in hex or ▶ Programs have at least 1 docking machine- ▶ Mach Lang programs are runs language on program ▶ Other programs are written in a program lang runs src on Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, which they run Compiler Construction compilers, & programs they were written What it looks like points: An interpreter 58 / 193 provides ▶ Interpreters come with 3 docking lang interpreter ▶ The language they provide ▶ The language [interpreter] on lang runs src on ▶ The [source] language in which Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, written Compiler Construction compilers, & programs What it looks like which they run 59 / 193 A compiler points: ▶ Compilers come with 4 docking compiling program ▶ The language they compile from compiler ▶ The language they compile to ▶ The language in which they were lang runs lang src dst on ▶ The language [interpreter] on Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, compilers, & programs Why bother with these pics?? compositions are correct Compiler Construction 60 / 193 ▶ Interpreters & compilers are often composed in complex ways ▶ Diagrams provide a simple, visual way to make sure that the Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, by the processor Compiler Construction compilers, & programs What it looks like 61 / 193 same machine-language interpreted running A machine language program machine- runs language on ▶ The program must be written in the program provides lang processor ▶ The two blocks join naturally Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, the language the program was Compiler Construction compilers, & programs written in (though we could!) What it looks like processor compiled into the same A compiled program running 62 / 193 machine-language interpreted by the ▶ The program must have been program lang runs src on provides lang ▶ The two blocks join naturally ▶ We are not saying anything about processor Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, language Compiler Construction compilers, & programs What it looks like 63 / 193 in a given language An interpreter running a compiled program (I) program ▶ Interpreters are similar to processors lang runs src on ▶ They execute/evaluate programs provides lang ▶ Interpreters are programs too! interpreter ▶ Written in some source language lang runs src on ▶ Compiled into some target provides lang ▶ They run on an interpreter: processor ▶ a processor (hardware) ▶ a program (another interpreter) Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, source, and Compiler Construction compilers, & programs What it looks like executed right) as target 64 / 193 program (II) An interpreter running a compiled another language. Note that the programs that were compiled from compiler program ▶ Interpreters can execute/evaluate lang runs src on compiling program compiler program lang runs lang lang runs src dst src on on ▶ takes the program (on top) as provides lang interpreter lang runs src on ▶ outputs the program (on the provides lang processor ▶ It is the target program that is Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, interpreter Compiler Construction compilers, & programs What it looks like compiler 65 / 193 program (III) which the compiler executes. An interpreter running a compiled program ▶ We may add additional details lang runs src on ▶ the processor/interpreter on compiling program compiler program lang runs lang lang runs src dst src on on ▶ We are still missing details provides provides lang lang ▶ the compiler that compiled the processor interpreter lang runs src on provides ▶ the compiled that compiled the lang processor ▶ …this can go on! Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, compilers, & programs Cross-compilers one one which the [compiled] program runs Compiler Construction 66 / 193 ▶ The processor on which the compiler runs is difgerent from the ▶ It crosses the boundaries of architectures. ▶ Java compiler javac is an example of a cross-compiler: ▶ It runs on [e.g.,] x86 ▶ It generates Java-byte-code that runs on the JVM ▶ The JVM is an interpreter ( java ) running on [e.g.,] x86 Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, slowdown, this is not really a Compiler Construction compilers, & programs What it looks like actually does this! stacked up as towers of interpreters tower! 67 / 193 tower Towers of interpreters height of the tower ▶ Interpreters may be stacked up in a program lang src runs on ▶ Towers of interpreters consume provides lang interpreter resources that are exponential to the runs lang src on provides lang ▶ Unless there is a marked interpreter lang runs src on provides lang interpreter ▶ Virtual machines (VMs) can be lang runs src on provides lang ▶ IBM mainframe architecture processor Mayer Goldberg \ Ben-Gurion University
Composing & combing processors, interpreters, compilers, & programs How are compilers and interpreters made? of composing & combining compilers and interpreters… Compiler Construction 68 / 193 ▶ Using previously-written compilers and interpreters, of course! ▶ This process is known as bootstrapping, and it is a specifjc form Mayer Goldberg \ Ben-Gurion University
Bootstrapping (I) x86 Compiler Construction mainframe! detach from the mainframe! re-done from scratch in x86 assembly language if we are to mainframe x86 exe x86 asm x86 c 2 x86 asm compiler x86 exe x86 asm c 3 c 1 c 1 written in compiled by runs on compiles x86 asm outputs pascal ibm pascalvs ibm 370 x86 asm x86 exe c 2 69 / 193 ▶ c 1 is an assembler acting as a cross-compiler ▶ c 2 already runs on our PC, but it was created on an IBM ▶ All the efgort of writing an assembler (in Pascal) has to be ▶ Any updates, upgrades, bug fjxes, changes, require that we re-compile c 2 on the mainframe! ▶ c 3 is essentially c 2 compiling itself ▶ With c 3 , we are free from our old environment: Pascal on IBM Mayer Goldberg \ Ben-Gurion University
Bootstrapping (II) x86 exe Compiler Construction compiler supports! x86 exe C (v. 0.2) x86 c 5 C (v. 0.2) c 6 x86 exe C (v. 0.2) x86 compiler C (v. 0.1) c 5 c 4 C (v. 0.1) x86 asm written in compiled by runs on x86 outputs c 3 compiles c 2 x86 x86 asm x86 exe c 4 x86 asm c 3 70 / 193 ▶ With c 4 we’re diverging: ▶ c 4 is a C compiler ▶ We don’t yet support many features ▶ c 5 is a C compiler written in C! Notice that ▶ it is written in an older version of C (v. 0.1) ▶ it supports a newer version of C (v. 0.2) ▶ In writing c 6 , we fjnally get to use all the language features our Mayer Goldberg \ Ben-Gurion University
Why study compiler construction course Compiler Construction 71 / 193 ▶ Almost all of you shall use compilers ▶ Most of you shall never work on another compiler after this ☞ So why study an entire course on writing compilers?? Mayer Goldberg \ Ben-Gurion University
Why study compiler construction ( cont ) There are many benefjts to studying compilers language Compiler Construction 72 / 193 ▶ Better understanding of programming languages ▶ Reduce the learning-curve for learning a new programming ▶ Better understanding of what compilers can & cannot do ▶ Demystify the compilation process ☞ Compilers are examples of code that writes code Mayer Goldberg \ Ben-Gurion University
bugs never re-appear Code that writes code Compiler Construction 73 / 193 ▶ Like having a team of programmers working for you ▶ Save time; Write code quickly ▶ Gain consistency ▶ Spread your bugs everywhere 🎊 ▶ A bug in the code generator will spread bugs to many places ▶ This actually makes the bugs easier to fjnd! ▶ Once debugged, the code is generated again, and the same Mayer Goldberg \ Ben-Gurion University
Why study compiler construction ( cont ) Bottom line programmer Compiler Construction 74 / 193 ▶ Knowledge of how compilers work will make you a more efgective ▶ Learning to write code that writes code is a force-multiplying technique you can use anywhere (think DSLs!) Mayer Goldberg \ Ben-Gurion University
Further Reading Introduction) Compiler Construction 75 / 193 🕯 Modern compiler design (2nd edition), Page 1 (Section 1: 🔘 Self hosting 🔘 Bootstrapping 🔘 Interpreters Mayer Goldberg \ Ben-Gurion University
Chapter 1 Goals Agenda Compiler Construction 76 / 193 🗹 Establishing common language & vocabulary 🗹 Understanding the “big picture” 🗹 Some background in programming languages ▶ Abstraction ▶ Dynamic vs Static ▶ Functional vs Imperative languages 🗹 Introduction to compiler construction ☞ Introduction to the ocaml programming language Mayer Goldberg \ Ben-Gurion University
Languages used in this course In this course, we shall be working with 3 languages: language Compiler Construction 77 / 193 ▶ The language in which to write the compiler: ocaml ▶ The language we shall be compiling: Scheme ▶ The language we shall be compiling to: x86/64 assembly Mayer Goldberg \ Ben-Gurion University
Introduction to ocaml (1) languages Compiler Construction 78 / 193 ▶ ML is a family of statically-typed, quasi-functional programming ▶ The main members of ML are ▶ SML (Standard ML) ▶ ocaml ▶ In Microsoftese , ocaml is called F#… Mayer Goldberg \ Ben-Gurion University
What kind of language is ocaml Ocaml — rich toolset Compiler Construction 79 / 193 ▶ is used all over the world ▶ is used in commercial and open source projects ▶ is powerful, effjcient, convenient, modern, elegant, and has a ▶ supports both functional and object-oriented programming ▶ The ocaml object system is very powerful! ▶ makes it very diffjcult to have run-time errors! Mayer Goldberg \ Ben-Gurion University
The advantages of learning ocaml system programming, etc Compiler Construction 80 / 193 ▶ Very rich language ▶ Great support for abstractions of various kinds ▶ Great library support: dbms, networking, web programming, ▶ Compiles effjciently, either to bytecode or native Mayer Goldberg \ Ben-Gurion University
Why we are using ocaml in the course programming sophisticated, abstract, clean, easy, elegant, re-usable, safe Compiler Construction 81 / 193 ▶ Pattern-matching, modules, object-orientation, and types make ▶ Easy to enforce an API Mayer Goldberg \ Ben-Gurion University
Getting, installing & using ocaml Compiler Construction 82 / 193 ▶ https://ocaml.org/ , or Mayer Goldberg \ Ben-Gurion University
Getting, installing & using ocaml ( https://www.gnu.org/software/emacs/ ) which is the best text editor. Period. in the line: #use "topfind";; This will load some basic tools you will want to use. Compiler Construction 83 / 193 ▶ I run ocaml under GNU Emacs ▶ Create the fjle .ocamlinit in your home directory, and place it Mayer Goldberg \ Ben-Gurion University
Getting, installing & using ocaml Compiler Construction 84 / 193 Mayer Goldberg \ Ben-Gurion University
Getting, installing & using ocaml http://www.algo-prog.info/ocaide/ , or Compiler Construction 85 / 193 ▶ You are free to use ocaml under any editor/environment you like ▶ For example, for ocaml under Eclipse, try OcaIDE at Mayer Goldberg \ Ben-Gurion University
Further Reading Whitington Yaron Minsky & Anil Madhavapeddy http://caml.inria.fr/pub/docs/manual-ocaml/ , or Compiler Construction 86 / 193 🕯 OCaml from the Very Beginning, by John Whitington 🕯 More OCaml: Algorithms, Methods & Diversions, by John 🕯 Real World OCaml: Functional programming for the masses, by 🕯 Practical OCaml, by Joshua B. Smith 🔘 The online manual at Mayer Goldberg \ Ben-Gurion University
Expressions & types Compiler Construction 87 / 193 ▶ Ocaml is a functional programming language ▶ Ocaml is interactive ▶ You enter expressions at the prompt, and get their values and their types ▶ Expressions are ended with ;; Mayer Goldberg \ Ben-Gurion University
Expressions & types - : float = 3.1415 Compiler Construction - : int list list = [[1]; [2; 3]; [4; 5; 6]] # [[1]; [2; 3]; [4; 5; 6]];; - : int list = [1; 2; 3; 5; 8; 13] # [1; 2; 3; 5; 8; 13];; # 3.1415;; An interaction at the ocaml prompt: - : char = 'm' # 'm';; - : string = "asdf" # "asdf";; - : int = 3 # 3;; 88 / 193 Mayer Goldberg \ Ben-Gurion University
What’s available?? Modules system variables, while controlling their visibility modules. Compiler Construction 89 / 193 ▶ We shall learn about modules later on, as part of the module ▶ In the meantime,modules are ways of aggregating functions & ▶ Functionality in ocaml is managed via loading and using Mayer Goldberg \ Ben-Gurion University
What’s available?? Directives Some useful directives Compiler Construction 90 / 193 ▶ Commands that start with # ▶ Non-programmable ▶ Tell you about the run-time system ▶ Change the run-time system ▶ #list;; to list available modules ▶ #cd <string>;; to change to a directory ▶ #require <string>;; to specify that a module is required ▶ #show_module <module>;; to see the signature of the module ▶ #trace <function>;; to trace a function ▶ #untrace <function>;; to untrace a function Mayer Goldberg \ Ben-Gurion University
What’s available?? What directives are available? Hashtbl.iter (fun k _v -> print_endline k) Toploop.directive_table;; This is nasty! We can defjne a function to do that: let directives () = Hashtbl.iter (fun k _v -> print_endline k) Toploop.directive_table;; and now we can just run directives();; to see the list of directives. Compiler Construction 91 / 193 Mayer Goldberg \ Ben-Gurion University
What’s available? Pervasives Compiler Construction ... exception Exit val failwith : string -> 'a val invalid_arg : string -> 'a exn -> 'a = "%raise_notrace" external raise_notrace : external raise : exn -> 'a = "%raise" sig module Pervasives : get! ocaml. 92 / 193 ▶ The module Pervasives contains all the “builtin” procedures in ▶ Try executing #show_module Pervasives;; and see what you Mayer Goldberg \ Ben-Gurion University
Integers in ocaml # 1 + 2;; - : int = 3 # 3 * 4;; - : int = 12 # 8 / 3;; - : int = 2 # 8 mod 3;; - : int = 2 Compiler Construction 93 / 193 Mayer Goldberg \ Ben-Gurion University
Read your error messages! # 1.2 + 3.4;; Characters 0-3: 1.2 + 3.4;; ^^^ Error: This expression has type float but an expression was expected of type int # cos(3);; Characters 3-6: cos(3);; ^^^ Error: This expression has type int but an expression was expected of type float Compiler Construction 94 / 193 Mayer Goldberg \ Ben-Gurion University
Floating-point numbers in ocaml Operators take a . after them to denote fmoating-point ops: # 3.4 +. 4.5;; - : float = 7.9 # 3.2 *. 5.1;; - : float = 16.32 # cos(2.0);; - : float = -0.416146836547142407 Compiler Construction 95 / 193 Mayer Goldberg \ Ben-Gurion University
Booelans in ocaml # true;; Compiler Construction - : bool = true # 3 != 4;; - : bool = false # 3 = 4;; - : bool = true # 3 = 3;; - : bool = false # false || false;; - : bool = false # true && false;; - : bool = false # false;; - : bool = true 96 / 193 Mayer Goldberg \ Ben-Gurion University
Read your error messages! In ocaml, unlike in Scheme, the then -clause and else -clause of if -expressions must be of the same type! # if 3 = 3 then 123 else 456;; - : int = 123 # if 3 = 4 then "moshe" else "yosi";; - : string = "yosi" # if 4 = 4 then 123 else "moshe";; Characters 23-30: if 4 = 4 then 123 else "moshe";; ^^^^^^^ Error: This expression has type string but an expression was expected of type int Compiler Construction 97 / 193 Mayer Goldberg \ Ben-Gurion University
Bitwise Boolean functions over the integers # 5 land 3;; - : int = 1 # 8 lor 3;; - : int = 11 # 5 lxor 3;; - : int = 6 Compiler Construction 98 / 193 Mayer Goldberg \ Ben-Gurion University
Characters in ocaml # '*';; - : char = '*' # '\t';; - : char = '\t' # '\n';; - : char = '\n' # '\\';; - : char = '\\' # '\"';; - : char = '"' # '\065';; - : char = 'A' Compiler Construction 99 / 193 Mayer Goldberg \ Ben-Gurion University
Strings in ocaml # "moshe!";; - : string = "moshe!" # "moshe\n";; - : string = "moshe\n" # "hello" ^ " " ^ "world";; - : string = "hello world" # "moshe".[3];; - : char = 'h' #show_module String;; will show you what string functions are available Compiler Construction 100 / 193 Mayer Goldberg \ Ben-Gurion University
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