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README.md
type-unlambda
Unlambda interpreter implemented in TypeScript's type system.
Getting Started
Installation:
npm install --save-dev typescript
npm install --save-dev @esolangs/type-unlambda
Example usage:
import Unlambda from '@esolangs/type-unlambda';
type Code = '``@c`d``s`|k`@c';
type Input = 'Hello!';
type Output = Unlambda<Code, Input>; // Output == '!olleH'
Screenshots (from Visual Studio Code):
Notes
You're likely to get the following error when trying to run a program with type-unlambda:
Type instantiation is excessively deep and possibly infinite.ts(2589).
To write loops in TypeScript's type system, we have to use recursions, like we do in other purely functional programming languages. Meanwhile, we use CPS to implement continuations, which also introduces heavy recursion.
However, TypeScript's type system is not meant for general purpose programming. There is no TCE, and recursion has its limits.
In src/compiler/checker.ts, there is a hard-coded limit for type instantiation:
if (instantiationDepth === 50 || instantiationCount >= 5000000) {
// ...
return errorType;
}
You may expect that there is an option somewhere that this limit can be
configured, like -ftemplate-depth=n
in gcc/clang. Unfortunately, there isn't,
and it's likely to stay that way.
To workaround this limitation, we modify the code of tsserver
or tsc
in node_modules
, until the error no longer applies. Changing
instantiationDepth
to 1000
is sufficient to run the example above.