g-ford/cradle

Let's Build a Compiler (in Haskell)

cradle's Issues

Small bugs in the haskell code snippets

In the "Single Digit Math" Chapter:

1. Section "A Single Digit" (first code snippet):
   module Data.Char should be replaced with
   import Data.Char.
2. Section "Adding Types":
   The data type has a terminal type Num Int, but it is instantiated with a Char in isDigit x = Num x.
   Either change the Num Int to Num Char or construct it with the ordinal value of the character: isDigit x = Num ((ord x)-(ord '0'))

Maybe not that important in general, but for someone not proficient in haskell like me, it took a while to find why the codes are not compiling.

Error in code snippet - Chapter Single Digit Math

function created to compute expression :
expression (x:y:z:[]) = (term x) ++ (addOperation y) ++ (term z)

shows a type error

    • Couldn't match expected type ‘[Char]’ with actual type ‘Char’
    • In the second argument of ‘(++)’, namely ‘(term z)’
      In the second argument of ‘(++)’, namely
        ‘(addOperation y) ++ (term z)’
      In the expression: (term x) ++ (addOperation y) ++ (term z)
   |
17 | expression (x:y:z:[]) = (term x) ++ (addOperation y) ++ (term z)
   |                                                          ^^^^^^

Possible but immature(imo) solution(or hack) that I came up with is
expression (x:y:z:[]) = (term x : []) ++ (addOperation y) ++ (term z : [])