# Aspirations and Design Principles for the Ginger Language, Interpreter and Virtual Machine¶

## Aspirations¶

Ginger is a modern programming language designed with the needs of part-time programming in mind. It has some nice XML processing features to make working with the web and Internet straightforward. The language features are properly separated, scrubbed of hard-to-learn corner cases, and clearly reflected in the default “Common” syntax. If you prefer to use a more familiar C-like syntax, that’s well-supported too, along with several others. This design means that if you only use Ginger part-time, you’re likely to find it easy to come back to despite the breaks.

Ginger is also designed to be powerful enough for substantial professional programming projects. We have ensured that it works elegantly as a scripting language, can also be compiled reasonably well, permits rich type annotations and has an advanced package system.

The most similar well-known language is probably Common LISP (with CLOS, the Common Lisp Object System). But Ginger has a rich Algol-like external syntax, an XML transport form, and multiple values are a central, well-integrated feature. The way Ginger deals with multiple values is, we think, is what most programmers will find striking about the language.

We hope it will be your “Other Programming Language”.

## Design Rules for the Ginger Programming Language¶

This is an attempt to articulate the design rules that we have employed in the development of the Ginger language. The rules are guidelines, not laws. Wherever we can, rules should be phrased both positively and negatively.

### General¶

• Compositionality - is the grand theme of Ginger. As much as possible we want to be able to build large units by sticking together small units. This applies to functions, classes, packages and everything else.
• Restriction - when restrictions are introduced into the language, it should be possible to relax them without altering the meaning of existing programs (e.g. the early discussion of semi-colon elected to demand zero-results and not automatically force zero-results, which meant when we relaxed that rule everything carried on working.)
• Library code has no magic features that user procedures cannot duplicate.
• All features are packaged so that a programmer can make use of them separately - not as part of some pre-determined task.
• Patterns in language andn library features should be complete. We strive to fit features into memorable patterns and wherever we start a pattern we strive to complete it. Omissions are treated as breaking the pattern and we hate breaking patterns.
• Access is never forbidden, it merely requires explicit permission. The key principle is that the the programmer is in charge of the virtual machine (but their decisions are published and can be vetoed by users.)
• Defaults always give the weakest capabilities (e.g. assignability must be explicitly requested.) Capabilities are not access rights but semantic features. Where a capability is not requested, the programmer is implicitly offering the compiler the freedom to exploit the absence of the capability.
• Simplify complexity, not trivialise simplicity. We seek to turn the difficult into straightforward rather than turning the simple into the trivial. Some programming languages have focused too hard on improving the power of expression for simple task. In striving to simplify the trivial, they introduce rules “for programmer convenience” that compromise more complex tasks. For example, some scripting languages automatically convert strings to numbers when performing arithmetic - but we see this as a pointless micro-convenience that just makes it harder to write large, robust programs.
• We say “If one, why not many?” We strive to generalize features to support multiplicity; multiple values, multiple inheritance, multiple dispatch, multiple threads of execution, etc.
• Symmetry - nothing should be distinguished or privileged without extraordinary justification.
• Features shouldn’t come with a safety manual. (“Gotcha-free”)
• Feature orthogonality is emphasized e.g. mutable numbers. Exceptions to the design are rejected.
• Safe, Robust, Defended - Ginger has a robust run-time system and safe libraries. Classes are designed to be correct in preference to fast or compact. (We would like them to be fast and compact too. But we won’t compromise robustness.)
• We believe that Java sets the new benchmark for language design - Ginger must step up to this mark everywhere.
• Where convenient, Ginger incorporates means for including constants written in other widespread notations.
• Ginger is not about preventing access but preventing accidents.
• Big but friendly! Feels much smaller than it actually is because of its strong regularity.

### Ginger Programmers¶

• The programmer is always in charge - not the IDE.

• Ginger is suitable for occasional programmers. An occasional programmer is one who has big breaks between their programming work. So they might be students, web site builders, part-time workers, or full-time programmers with a different main programming language.

We want Ginger to be the language people turn to for their own projects. We call this being their “other” programming language. We believe this is the most sincere form of appreciation and its our passionate goal.

• Ginger is scaleable for team programming.

### Variable Names and Package Names¶

• Variable names are sequences of Unicode characters of arbitrary length. In particular there are no reserved words in the abstract language, only in concrete syntaxes. Therefore all concrete syntaxes must support names being arbitrary Unicode strings.
• Variable names are not overloaded. In particular, no overloading of procedures is allowed. (In this context, overloading means that a single name in a single lexical context could denote two different variables.)
• The programmer is free to name variables and packages as they please because they are in charge. If there are relationships between variables or packages in the language, they cannot be implied by a naming convention. (The programmer is free to do otherwise, of course. They are in charge.) This implies that the suggested convention for “fast” packages is wrong.

### Syntax-Agnostic and Data File Formats¶

• We want Ginger to have multiple concrete syntaxes. Some of our programmers will be programming regularly in a different “primary” language and we want them to feel welcome when they pick up Ginger .
• Although there will be a Common syntax (the word ‘standard’ must be shunned) this must not imply that it has any special privilege. The name “Common” is chosen to suggest friendliness and shared ownership and the word “standard” must be firmly avoided – along with any attempt to give it a special role. Some of these syntaxes will be general and able to express arbitrary programs, others will be special purpose and very limited.
• Pre-existing external formats such as CSV, XML, GIF, JPEG and so on will be given standard (or default) loaders. This mechanism allows the Ginger programmer to treat these external formats as another way to write named constants.
• We will define an AbstractSyntaxTree & its mapping to an XML transport format.

### Common Syntax¶

Some of our programmers will be students and not have a strong preference for a particular style of syntax. Some of our experienced programmers will be looking for a syntax that is neither a crash of symbols nor a tedious exercise in form-filling. We think the Common syntax may be for them.

Common is a modern syntax designed to be memorable, consistent, readable and resilient against common mistakes. For example, languages with the fragile C/Java syntax are vulnerable to the following common mistake.

if ( this.test() )
this.FirstThing();
this.SecondThing();    // Supposed to be inside the if.


Common guards against this mistake by arranging that keywords such as if have their textual scope delimited by a matching closing keyword – in this case endif. This is how it might look in Common.

if this.test() then          // Cryptic brackets replaced by "then"
this.FirstThing();
this.SecondThing();      // Much harder to make the mistake.
endif;


Here’s a list of our goals.

• Terseness is not a goal but is welcome.
• We are comfortable with a degree of verbosity - but excessive verbosity is unwelcome.
• Reserved words will never be one alphabetic character long.
• Macro capability for standard syntax.
• Syntax for literal objects generates immutable run-time objects. This means that the programmer can be assured that literal syntax remains true throughout a program run. It also follows the rule of fewest capabilities.
• Where it does not conflict with other more pressing concerns, the common syntax shall borrow from other programming languages in order to reduce the effort of cross-training.
• The common syntax employs the usual reserved word strategy to distinguish special keywords from ordinary identifiers. However, we see that as a convention for programming without text styling. It is preferable to distinguish reserved words by their styling. A Ginger IDE should support styling.
• Common: The common syntax will support programming in the ASCII character set by default but will include Unicode alternatives. We see the Unicode alternatives as the preferred option and when writing in Unicode becomes commonplace we may deprecate the ASCII versions. A Ginger IDE should support Unicode.

### Semantics¶

• Evaluation order is specified

### Type Checking¶

• A valid type assertion will never prevent a program from compiling (the Dollin Principle).
• An Ginger implementation is not ‘’required’’ to do any type checking. Of course, one that omits type checking would be omitting a chunk of important and useful functionality. But it would be a perfectly viable implementation.
• A Ginger implementation is not ‘’required’’ to perform any type inference.

### Compilation and Performance¶

• We aim to be macro-efficient rather than micro-efficient. We are only mildly interested in benchmarks that test how efficient code generation is on the small scale. We are much more interested in the performance of garbage collection, coroutine switching, etc.
• Performance enhancing assertions are either checked at compile-time or there is an option to check them at run-time which is, by default, enforced.
• We aim to be in the compilation sweet spot of simplicity versus performance. We believe that this sweet spot exists.
• Features that are potentially expensive to implement, such as multiple dispatch, are more acceptable if the programmer only incurs the penalty for using the feature (or using libraries that use the feature).
• The target execution environment is the desktop computer.

### Interactive Development Environment (IDE)¶

• The programmer is in charge.
• Ginger IDE may warn but may not obstruct (which is one of the things we we mean by the programmer being in charge).
• A type-error detected at compile-time will not lead to an interaction that forces a programmer to correct it before proceeding to running and debugging.
• Top-level definitions may appear in packages according to the programmer’s organisational principles and not implementation concepts such as the class hierarchy.
• The compiler is free to assume it knows the full range of capabilities and only supply the minimum set needed. So the programmer cannot legitimately expect capabilities to be dynamically added on demand. For example, when the compiler sees val x := 99 it is under no obligation to allocate store to represent x!! As a consequence, the programmer is not able to force an assignment without a recompilation.
• A Ginger IDE should support Unicode and text styling as per the aims of the Common syntax.
• It must be easy and practical to program Ginger without an IDE.