eval could be simpler

hoosierEE · May 13, 2024 · 042cf94 · 042cf94
1 parent 018d7ab
commit 042cf94
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Showing 5 changed files with 50 additions and 134 deletions.
diff --git a/prototype/Eval.py b/prototype/Eval.py
@@ -4,7 +4,7 @@
 # use plain Python values instead of Val class
 from Ast import Ast
 from Builtin import ASSIGN,VERB
-from Semantic import lamp,formalize
+from Semantic import lam_from_prj,formalize
 class Sym(str):pass
 class Name(str):pass
 class Num(float):pass
@@ -56,7 +56,7 @@ def v2(op,x,y):
 
 def evl(x:Ast,e=None) -> object:
  e = e or {}
- x = formalize(lamp(x))
+ x = formalize(lam_from_prj(x))
  return Eval(e,x)
 
 def Eval(e:dict,x:Ast) -> object:

diff --git a/prototype/Semantic.py b/prototype/Semantic.py
@@ -14,21 +14,17 @@
 from Ast import Ast
 from Builtin import ASSIGN,VERB
 
-def lamc(a:Ast) -> Ast:
- '''composition ⇒ lambda'''
- ...
-
-def lamp(a:Ast) -> Ast:
- '''projection ⇒ lambda'''
+def lam_from_prj(a:Ast) -> Ast:
+ '''convert projection to lambda'''
  ax,ay = Ast('x'),Ast('y')
  match a.node,len(a.children):
   case 'prj',1:
    if (v:=a.children[0].node)[0] in VERB and v.endswith(':'):
     return Ast('{',Ast('[',ax), Ast(v,ax))
    return Ast('{',Ast('[',ax,ay), Ast(v,ax,ay))
   case 'prj',2:
-   return Ast('{',Ast('[',ax), Ast(a.children[0].node,lamp(a.children[1]),ax))
- return Ast(a.node, *map(lamp,a.children))
+   return Ast('{',Ast('[',ax), Ast(a.children[0].node,lam_from_prj(a.children[1]),ax))
+ return Ast(a.node, *map(lam_from_prj,a.children))
 
 def get_params(a:Ast) -> str:
  '''get x y z arguments from lambdas'''

diff --git a/prototype/Unit.py → prototype/Test.py b/prototype/Unit.py → prototype/Test.py
diff --git a/prototype/_eval1.py b/prototype/_eval1.py
diff --git a/prototype/lisp.py b/prototype/lisp.py
@@ -0,0 +1,44 @@
+# lisp.py: λ-calculus with integers, subtraction, variables, conditionals, and closures.
+# NOTE: Split and Parse courtesy of https://www.norvig.com/lispy.html
+def Split(x:str)->list:
+  return x.replace('(',' ( ').replace(')',' ) ').split()
+
+def Parse(x:list)->list:
+  t = x.pop(0)
+  if t=='(':
+    l = []
+    while x[0]!=')': l.append(Parse(x))
+    x.pop(0)
+    return l
+  elif t==')':
+    raise SyntaxError('unexpected ")"')
+  else:
+    return int(t) if t.isnumeric() else t
+
+def Eval(e:dict,x:list|int|str)->int|list:#Eval({},Parse(Split('(if 1 42 43)')))
+  match x:
+    case int()|('lam',_,_):return x
+    case str():            return e[x]
+    case ('-',a,b):        return Eval(e,a)-Eval(e,b)
+    case ('let',a,b,c):    return Eval({**e,a:Eval(e,b)},c)
+    case ('if',a,b,c):     return Eval(e,b) if Eval(e,a) else Eval(e,c)
+    case (('lam',a,b),*c): return Eval({**e,**dict(zip(a,(Eval(e,i) for i in c)))},b)
+    case list():           return Eval(e,[Eval(e,i) for i in x])
+
+if __name__=="__main__":#unit tests
+  x = [a.strip() for a in '''
+  42 ⇒ 42
+  (- 1 4) ⇒ -3
+  (let x 1 (- 43 x)) ⇒ 42
+  (lam x (- 0 x)) ⇒ ['lam', 'x', ['-', 0, 'x']]
+  (if (- 3 3) 1 2) ⇒ 2
+  (if 42 1 2) ⇒ 1
+  ((lam x x) 3) ⇒ 3
+  (let f (lam x 3) (f 1)) ⇒ 3
+  '''.splitlines()[1:-1]]
+  sz = max(map(len,x))
+  for t in x:
+    i,o = t.split(' ⇒ ')
+    try: r = Eval({},Parse(Split(i)))
+    except Exception as e: print(f'failing test: {i}','\n',f'exception: {e}'); continue
+    print(f'{t:<{sz}}','✅' if str(r)==o else f'❌ got: {r}')