This is an implementation of a DSL using Happy. The DSL is the arithmetic language used in the Happy tutorial/documentation. This project is an interpreter for the DSL.
Build the interpreter with the following commands:
happy calc.y -o Calc.hs
ghc --make Calc.hs -outputdir=lib
Test the interpreter with this example, put the following text into a example.txt:
let x = 10 in
let y = 20 in
x + y
Evaluate the example with command, ./Calc example.txt which will generate the result 30.0.
I wrote the code in Interpret.hs, most of the rest comes from the tutorial.