237 lines
4.3 KiB
Markdown
237 lines
4.3 KiB
Markdown
lang0
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=====
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The base of language; a language designed to be just a compiler for other languages.
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And you probably won't write _your_ custom language in lang0, but in a system language built in lang0.
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The language
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---
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lang0 is designed for building small compilers. As such, it has a number of primitives specific for that.
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### Examples
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See `example0.lang0`:
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```
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main:
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declare char
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declare isa
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declare isnota
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calc char peek
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calc isa eq char "a"
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calc isnota not isa
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if isa
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emit "Got a"
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emit eol
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/
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if isnota
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emit "Did not get a"
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emit eol
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/
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return
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/
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```
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```sh
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make it2
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cat example0.lang0 | ./it2-out > example0.c
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gcc example0.c -o example0
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echo 'a' | ./example0
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# Got a
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echo 'b' | ./example0
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# Did not get a
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```
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### Formatting
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Indentation is done using tabs.
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### Parsing
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#### Pre declaration (functions)
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Functions need to be pre-declared if you intend to use them before you have defined them:
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```
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func result/
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...
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func result:
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return result
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/
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```
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#### Pre declaration (variables)
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Variables will need to be declared before you can use them:
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```
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func:
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declare result
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set result "Result"
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return result
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/
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```
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### Variables
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#### calc var func args*
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Calls func with args and stores the output in var.
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#### declare var
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Pre-declares var.
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#### set var "const"
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Sets var to "const".
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### Flow control
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#### break
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Exits the deepest `forever` loop.
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#### func args*
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Calls the function name `func` with the given arguments. The result, if any, is ignored.
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#### if arg
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Evaluates arg. If found to be true, descends in the block. Otherwise, skips the block
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#### forever
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Repeats the block until `break` or `return` is called.
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#### return var?
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Returns the given value. You can not give an argument if your function is never used in `call`.
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### Builtins
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#### check func [arg0..] : msg [arg0..]
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Calls the given function with the given arguments. If the function's return value is not found to be true, outputs the given `msg` and halts the program.
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#### trace
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Writes the name and value of the variable passed to stderr if the TRACE environment variable is set.
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### Standard library constants
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#### eof
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End of file character, zero byte.
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#### eol
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End of line character.
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#### quote
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Double quote character.
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### Standard library functions
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#### addstringchar a b
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`b` is expected to have length 1.
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Creates a new string with `b` appended to `a`.
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#### emit arg
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Writes the given string to standard output.
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#### eq a b
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Return true if the given strings are the same.
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#### lt a b
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`a` and `b` are expected to have length 1.
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Return true if a would sort before b.
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#### mapclear mapname
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Maps are global and can be used from any function.
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Clears all values set in the map named `mapname`.
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#### mapgetkey mapname key
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Maps are global and can be used from any function.
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Looks up `key` in the map named `mapname` and returns it.
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If not found, returns an empty string.
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#### mapsetkey mapname key value
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Maps are global and can be used from any function.
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Adds a mapping from `key` to `value` to the map named `mapname`.
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#### not a
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Returns "1" if a is empty; otherwise, returns "".
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#### peek
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Checks stdin for the next character and returns it.
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#### skip
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Advances stdin a single character.
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#### stdincolno
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Returns the column number for stdin (starting at 1)
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#### stdinlineno
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Returns the line number for stdin (starting at 1)
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### Typing
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Every variable is of type string. Every function gets a number of strings as output, and returns another string.
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The `if` statement accept all non-empty strings as true, and the empty string as false.
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Notes
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---
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You can declare variables and functions ahead of time. This is necessary for some interpreters.
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Bootstrap stairs
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---
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The first iteration is written by hand, both the compiler and the compiler compiler.
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It targets python3 as an interpreter.
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The second version only has the compile written by hand, with the compiler compiler being the output of iteration 1.
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It targets gcc as interpreter.
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We compile every iteration 3 times, to ensure that the the compiler round trips properly.
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How to run
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---
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Install python3 and make
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```sh
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make clean all
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```
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Get more info
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```
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make TRACE=1 clean all
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```
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You will now have a lang0 compiler in python for python in `./it1-out.py`, and one written in C for C in `./it2-out`.
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