75 lines
2.1 KiB
Cheetah
75 lines
2.1 KiB
Cheetah
module basic
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language fostr
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/** md
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Title: A whirlwind tour of fostr
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## Whirlwind tour
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fostr is just in its infancy, so it's not yet even ready for
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Hello, World. The best we can offer now is this little snippet
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that writes the sum of the ASCII codes for 'H', 'W', and '!' to standard output:
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```fostr
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**/
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/** md */ test emit_sum [[
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stdio << 72 + 87 + 33
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]]/* **/ parse to Receives(Stdio(), Sum([Int("72"), Int("87"), Int("33")]))
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/** writes
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192**/
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/** md
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```
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At the moment, there are only two ways to run a file containing fostr code
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(you can find the above in `tests/emit_sum.fos`). They both start by
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cloning this fostr project. Then, either:
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1. Open the project in Eclipse and build it, visit your program file,
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generate code from it in your preferred target language (among
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the options available in the "Spoofax > Generate" menu), and execute the
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resulting code.
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1. Use the `bin/fosgen` bash script to generate code in a target language,
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and execute the resulting code.
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For example, this snippet generates the following Python:
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```python
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{! ../tests/emit_sum.py extract:
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start: 'Stdio\s='
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!}
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```
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(which writes "192" to standard output), or this non-idiomatic, inefficient, but
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working Javascript:
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```javascript
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{! ../tests/emit_sum.js extract:
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start: '^}'
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!}
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```
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In either case, there's also a preamble defining Stdio that's generated.
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(Haskell code generation is also currently supported.)
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### Everything has a value
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As mentioned in the [Introduction](../README.md), everything in a fostr
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program (including the entire program itself) is an expression and has
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a value. So what's the value of that expression above? Well, `stdio` is our
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first example of a stream, and for convenience, the value of a stream
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receiving an item is just the stream back again. The `<<` operator is also
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left-associative, so that way we can chain insertions into a stream:
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```fostr
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**/
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/** md */ test emit_twice [[
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stdio << 72 + 87 + 33 << 291
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]]/* **/ parse to Receives(
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Receives(Stdio(), Sum([Int("72"), Int("87"), Int("33")])),
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Int("291"))
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/** writes
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192291**/
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/** md
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```
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Running this program produces a nice palindromic output: "192291".
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**/
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