简介 科学计算对性能一直有着最高的需求，但目前各领域的专家却大量使用较慢的动态语言来开展他们 的日常工作。偏爱动态语言有很多很好的理由，因此我们不会舍弃动态的特性。幸运的是，现代编 程语言设计与编译器技术可以大大消除性能折衷（trade-off），并提供有足够生产力的单一环境进行 原型设计，而且能高效地部署性能密集型应用程序。Julia 语言在这其中扮演了这样一个角色：它是 一门灵活的动态语言，适合 的运作方式后，写出和 C 一样快的代码对你而言就是小菜一碟。 Julia 拥有可选类型标注和多重派发这两个特性，同时还拥有很棒的性能。这些都得归功于使用 LLVM 实现的类型推导和即时编译（JIT）技术。Julia 是一门支持过程式、函数式和面向对象的多范式语言。 它像 R、MATLAB 和 Python 一样简单，在高级数值计算方面有丰富的表现力，并且支持通用编程。为 了实现这个目标，Julia a=b 中的 b 指的是外部作用域内的 b，而不是后续参数中的 b。 9.14. 函数参数中的 DO 结构 77 9.14 函数参数中的 Do 结构 把函数作为参数传递给其他函数是一种强大的技术，但它的语法并不总是很方便。当函数参数占据 多行时，这样的调用便特别难以编写。例如，考虑在具有多种情况的函数上调用 map： map(x->begin if x < 0 && iseven(x)

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function

documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function 1113 49.1 Example In the example below we use a scoped value to implement a permission check in a web-application. After determining the permissions of the request, a new dynamic scope is entered and

documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function 1107 49.1 Example In the example below we use a scoped value to implement a permission check in a web-application. After determining the permissions of the request, a new dynamic scope is entered and

documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function end 49.1 Example In the example below we use a scoped value to implement a permission check in a web-application. After determining the permissions of the request, a new dynamic scope is entered and

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function

100%|████████████████████████████████| Time: 0:00:00 Main binary filename not available. Serving web UI on http://localhost:62261 "alloc-profile.pb.gz" Then you can view the profile by navigating to documentation. – Interfaces for Julia packages are typically described using docstrings, README.md, static web pages, ... • Some developers choose not to export all symbols required to use their package/module Julia is running in a JavaScript VM (JSVM), including e.g. a WebAssembly JavaScript embedding in a web browser. Julia 1.2 This function requires at least Julia 1.2. source Base.Sys.loadavg – Function