PS: error handling, throw, print excpetions without dying.

10 files changed, 173 insertions, 54 deletions

diff --git a/docs/TODO b/docs/TODO
index 3c3df97..adb670c 100644
--- a/docs/TODO
+++ b/docs/TODO
@@ -17,6 +17,7 @@ All:
     - Print full exception when test gets EOF from expect
     - Note that bash 4, Java 1.7, php 5.3 required
     - Break out language eval into step0.5
+    - regular expression matching in runtest
 
 ---------------------------------------------
 
diff --git a/docs/step_notes.txt b/docs/step_notes.txt
index 703d855..c0cd35a 100644
--- a/docs/step_notes.txt
+++ b/docs/step_notes.txt
@@ -36,6 +36,11 @@ Step Notes:
         - read_atom
             - return scalar boxed type:
                 - nil, true, false, symbol, integer, string
+    - repl loop
+        - catch errors, print them and continue
+        - impls without exception handling will need to have a global
+          variable with checks for it at the beginning of critical
+          code sections
 
 - vectors
     - Basically: two array types that retain their boxed types, can be
@@ -103,7 +108,9 @@ Step Notes:
         - if:
         - fn*:
             - simple if language supports closures
-    - define not using rep()
+            - otherwise needs a way of representing functions that can
+              have associated metadata
+    - define "not" using REP/RE
 
 
 - metadata
diff --git a/ps/reader.ps b/ps/reader.ps
index 0fa4c02..8575d64 100644
--- a/ps/reader.ps
+++ b/ps/reader.ps
@@ -63,8 +63,8 @@
     /cnt 0 def
     { % loop
         idx str length ge { %if EOF
-            (Error: unexpected EOF reading string\n) print
-            error
+            (unexpected EOF reading string)
+            throw
         } if
         /ch str idx get def  % current character
         /idx idx 1 add def
@@ -119,8 +119,8 @@
     { % loop
         str idx read_spaces /idx exch def pop
         str length idx le { %if EOF
-            (Error: unexpected EOF reading list\n) print
-            error
+            (unexpected EOF reading list)
+            throw
         } if
         /ch str idx get def  % current character
         ch 41 eq { exit } if % ')' is end of list
@@ -159,9 +159,13 @@
     /ch str idx get def  % current character
     ch 40 eq { %if (
         str idx read_list
+    }{ ch 91 eq { %elseif [
+        (unexpected '[') throw
+    }{ ch 93 eq { %elseif ]
+        (unexpected ']') throw
     }{ % else
         str idx read_atom
-    } ifelse
+    } ifelse } ifelse } ifelse
 
     %(stack vvv\n) print
     %pstack
diff --git a/ps/step1_read_print.ps b/ps/step1_read_print.ps
index d08579c..e03c8cc 100644
--- a/ps/step1_read_print.ps
+++ b/ps/step1_read_print.ps
@@ -9,19 +9,17 @@
 
 
 % eval
-/EVAL {
+/EVAL { 2 dict begin
     % just "return" the "ast"
     /env exch def
     /ast exch def
     ast
-} def
+end } def
 
 
 % print
 /PRINT {
-    /exp exch def
-    %(printing: ) print exp ==
-    exp pr_str
+    pr_str
 } def
 
 
@@ -39,7 +37,13 @@
     not { exit } if  % exit if EOF
 
     %(\ngot line: ) print dup print (\n) print flush
-    REP print (\n) print
+    { %try
+        REP print (\n) print
+    } stopped {
+        (Error: ) print
+        get_error_data pr_str print (\n) print
+        clear
+    } if
 } bind loop
 
 (\n) print  % final newline before exit for cleanliness
diff --git a/ps/step2_eval.ps b/ps/step2_eval.ps
index 72a91fa..dec403c 100644
--- a/ps/step2_eval.ps
+++ b/ps/step2_eval.ps
@@ -14,7 +14,12 @@
     /ast exch def
     %(eval_ast: ) print ast ==
     /nametype ast type eq { %if symbol
-        env ast get
+        env ast known {
+            env ast get
+        }{
+            (') ast pr_str (' not found)
+            concatenate concatenate throw
+        } ifelse
     }{ /arraytype ast type eq { %elseif list
         [
             ast {
@@ -44,9 +49,7 @@ end } def
 
 % print
 /PRINT {
-    /exp exch def
-    %(printing: ) print exp ==
-    exp pr_str
+    pr_str
 } def
 
 
@@ -71,7 +74,13 @@ end } def
     not { exit } if  % exit if EOF
 
     %(\ngot line: ) print dup print (\n) print flush
-    REP print (\n) print
+    { %try
+        REP print (\n) print
+    } stopped {
+        (Error: ) print
+        get_error_data pr_str print (\n) print
+        clear
+    } if
 } bind loop
 
 (\n) print  % final newline before exit for cleanliness
diff --git a/ps/step3_env.ps b/ps/step3_env.ps
index c2e65cb..908ff43 100644
--- a/ps/step3_env.ps
+++ b/ps/step3_env.ps
@@ -41,7 +41,7 @@ end } def
         }{ /let* a0 eq { %if let*
             /a1 ast 1 get def
             /a2 ast 2 get def
-            /let_env env env_new def
+            /let_env env [ ] [ ] env_new def
             0 2 a1 length 1 sub { %for each pair
                 /idx exch def
                 let_env
@@ -63,14 +63,12 @@ end } def
 
 % print
 /PRINT {
-    /exp exch def
-    %(printing: ) print exp ==
-    exp pr_str
+    pr_str
 } def
 
 
 % repl
-/repl_env null env_new def
+/repl_env null [ ] [ ] env_new def
 
 /REP { READ repl_env EVAL PRINT } def
 /_ref { repl_env 3 1 roll env_set pop } def
@@ -91,7 +89,13 @@ end } def
     not { exit } if  % exit if EOF
 
     %(\ngot line: ) print dup print (\n) print flush
-    REP print (\n) print
+    { %try
+        REP print (\n) print
+    } stopped {
+        (Error: ) print
+        get_error_data pr_str print (\n) print
+        clear
+    } if
 } bind loop
 
 (\n) print  % final newline before exit for cleanliness
diff --git a/ps/types.ps b/ps/types.ps
index 5028c58..8843841 100644
--- a/ps/types.ps
+++ b/ps/types.ps
@@ -28,29 +28,29 @@
     aload % push array onto stack
     length -1 0 { 1 roll } for % reverse
     ]
-} def
+} bind def
 
-/pr_str {
-    %(in pr_str\n) print
-    /obj exch def
+/_pr_str { 4 dict begin
+    /print_readably exch def
+    dup
+    /func? exch xcheck def % executable function
+    /obj exch cvlit def
     /arraytype obj type eq { % if list
         % accumulate an array of strings
-        (\()
-        obj length 0 gt { %if any elements
-            [
-                obj {
-                    pr_str
-                } forall
-            ]
-            { concatenate ( ) concatenate } forall
-            dup length 1 sub 0 exch getinterval % strip off final space
-        } if
-        (\)) concatenate
+        func? { (<fn* { ) }{ (\() } ifelse
+        obj ( ) print_readably _pr_str_args
+        concatenate
+        func? { ( } >) }{ (\)) } ifelse
+        concatenate
     }{ /integertype obj type eq { % if number
         /slen obj 10 idiv 1 add def
         obj 10 slen string cvrs
     }{ /stringtype obj type eq { % if string
-        (") obj (") concatenate concatenate
+        print_readably {
+            (") obj (") concatenate concatenate
+        }{
+            obj
+        } ifelse
     }{ null obj eq { % if nil
         (nil)
     }{ true obj eq { % if true
@@ -58,18 +58,79 @@
     }{ false obj eq { % if false
         (false)
     }{ /nametype obj type eq { % if symbol
-        obj obj length string cvs
+        obj dup length string cvs
     }{
         (<unknown>) 
     } ifelse } ifelse } ifelse } ifelse } ifelse } ifelse } ifelse
+end } def
+
+% array delim print_readably -> _pr_str_args -> new_string
+/_pr_str_args { 3 dict begin
+    /print_readably exch def
+    /delim exch def
+    /args exch def
+    ()
+    args length 0 gt { %if any elements
+        [
+            args { %foreach argument in array
+                print_readably _pr_str
+            } forall 
+        ]
+        { concatenate delim concatenate } forall
+        dup length delim length sub 0 exch getinterval % strip off final delim
+    } if
+} def
+
+
+%
+% errors/exceptions
+%
+
+% data -> throw ->
+% Takes an arbitrary data and puts it in $error:/errorinfo. Then calls
+% stop to transfer control to end of nearest stopped context.
+/throw {
+    $error exch /errorinfo exch put
+    $error /command /throw put
+    stop
+} def
 
-    %(pr_str2 stack vvv\n) print
-    %pstack
-    %(pr_str2 stack ^^^\n) print
+/errorinfo? {
+    $error /errorinfo known { % if set
+        $error /errorinfo get null ne {
+            true
+        }{
+            false
+        } ifelse
+    }{
+        false
+    } ifelse
 } def
 
+/get_error_data {
+    errorinfo? { %if
+        $error /errorinfo get
+    }{
+        $error /errorname get 255 string cvs
+        (: ) 
+        $error /command get 99 string cvs
+        ( at )
+        $error /position get 10 99 string cvrs
+        concatenate
+        concatenate
+        concatenate
+        concatenate
+    } ifelse
+} def
 
+
+
+%
 % list operations
+%
+/_list? {
+    dup xcheck not exch type /arraytype eq and
+} def
 /_first { 0 get } def
 /_rest { dup length 1 sub 1 exch getinterval } def
 /_nth { get } def
@@ -78,10 +139,24 @@
 %
 % Env implementation
 %
-/env_new { 1 dict begin
+% outer binds exprs -> env_new -> new_env
+/env_new { 3 dict begin
+    %(in env_new\n) print
+    /exprs exch def
+    /binds exch def
     /outer exch def
     << 
         /__outer__ outer
+        0 1 binds length 1 sub {
+            /idx exch def
+            binds idx get (&) eq { %if &
+                binds idx 1 add get % key
+                exprs idx   exprs length idx sub   getinterval % value
+                exit
+            } if
+            binds idx get % key
+            exprs idx get % value
+        } for
     >>
 end } def
 
@@ -97,13 +172,14 @@ end } def
     } ifelse } ifelse
 end } def
 
-/env_set { 3 dict begin
-    /func dup xcheck def
+/env_set { 4 dict begin
+    dup
+    /func? exch xcheck def % executable function
     /val exch cvlit def
     /key exch def
     /env exch def
-    env key val func { cvx } if put
-    val func { cvx } if
+    env key val func? { cvx } if put
+    val func? { cvx } if
 end } def
 
 /env_get { 2 dict begin
@@ -111,8 +187,11 @@ end } def
     /env exch def
     env key env_find
     dup null eq {
-        (Error: ') print key 99 string cvs print (' not found\n) print
-        error
+        (')
+        key 99 string cvs
+        (' not found)
+        concatenate concatenate
+        throw
     }{
         key get
     } ifelse
diff --git a/python/step2_eval.py b/python/step2_eval.py
index bb5d6f8..65972a2 100644
--- a/python/step2_eval.py
+++ b/python/step2_eval.py
@@ -12,7 +12,10 @@ def READ(str):
 # eval
 def eval_ast(ast, env):
     if symbol_Q(ast):
-        return env[ast]
+        try:
+            return env[ast]
+        except:
+            raise Exception("'" + ast + "' not found")
     elif list_Q(ast):
         return new_list(*map(lambda a: EVAL(a, env), ast))
     elif vector_Q(ast):
diff --git a/tests/step1_read_print.mal b/tests/step1_read_print.mal
index f0d7a9a..de7fcc1 100644
--- a/tests/step1_read_print.mal
+++ b/tests/step1_read_print.mal
@@ -60,7 +60,6 @@ abc-def
   ( +   1   (+   2 3   )   )  
 ;=>(+ 1 (+ 2 3))
 
-
 ;; Testing read of vectors
 [+ 1 2]
 ;=>[+ 1 2]
@@ -71,7 +70,6 @@ abc-def
   [ +   1   [+   2 3   ]   ]  
 ;=>[+ 1 [+ 2 3]]
 
-
 ;; Testing read of hash maps
 {"abc" 1}
 ;=>{"abc" 1}
@@ -109,4 +107,11 @@ abc-def
 @a
 ;=>(deref a)
 
-
+;;
+;; Testing reader errors
+(1 2
+; expected ')', got EOF
+[1 2
+; expected ']', got EOF
+"abc
+; expected '"', got EOF
diff --git a/tests/step2_eval.mal b/tests/step2_eval.mal
index 33c7b17..b24af93 100644
--- a/tests/step2_eval.mal
+++ b/tests/step2_eval.mal
@@ -11,6 +11,9 @@
 (/ (- (+ 5 (* 2 3)) 3) 4)
 ;=>2
 
+(abc 1 2 3)
+; .*\'abc\' not found.*
+
 ;; Testing evaluation within collection literals
 [1 2 (+ 1 2)]
 ;=>[1 2 3]