This article is a repost of an ADR from Matanuska BASIC, my attempt to write a BASIC interpreter in TypeScript.
Context
In a traditional BASIC, the let keyword is used for both defining variables and assigning new values to them. But this keyword is also optional - most BASIC interpreters understand i% = 1 and let i% = 1 to be synonymous.
On the other hand, many modern languages have semantic division between definition and assignment. For example, JavaScript defines variables with let or const, and uses a simple = for assigning to existing variables. This allows JavaScript to distinguish between local and non-local (or global) variables.
Python handles this in reverse - a simple = will define a local variable if it's unassigned, but the nonlocal and global keywords will allow for assigning to those kinds of variables.
Decision
In Matanuska, let will be used for defining variables, and a simple = will be used for assignment. This will allow supporting non-local variables in the future, while having syntax and idioms similar to a traditional BASIC.
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