Implementing macros.

[scheme.forth.jl.git] / scheme.4th

diff --git a/scheme.4th b/scheme.4th
index 0a237da..5a049d4 100644 (file)
--- a/scheme.4th
+++ b/scheme.4th
@@ -28,6 +28,7 @@ make-type boolean-type
 make-type character-type
 make-type string-type
 make-type nil-type
+make-type none-type
 make-type pair-type
 make-type symbol-type
 make-type primitive-proc-type
@@ -36,7 +37,7 @@ make-type fileport-type
 : istype? ( obj type -- obj bool )
     over = ;
 
-\ ------ List-structured memory ------ {{{
+\ ---- List-structured memory ---- {{{
 
 10000 constant scheme-memsize
 
@@ -112,6 +113,9 @@ variable nextfree
 : nil 0 nil-type ;
 : nil? nil-type istype? ;
 
+: none 0 none-type ;
+: none? none-type istype? ;
+
 : objvar create nil swap , , ;
 
 : value@ ( objvar -- val ) @ ;
@@ -264,13 +268,15 @@ objvar symbol-table
     does> dup @ swap 1+ @
 ;
 
-create-symbol quote     quote-symbol
-create-symbol define    define-symbol
-create-symbol set!      set!-symbol
-create-symbol ok        ok-symbol
-create-symbol if        if-symbol
-create-symbol lambda    lambda-symbol
-create-symbol λ         λ-symbol
+create-symbol quote         quote-symbol
+create-symbol define        define-symbol
+create-symbol define-macro  define-macro-symbol
+create-symbol set!          set!-symbol
+create-symbol ok            ok-symbol
+create-symbol if            if-symbol
+create-symbol lambda        lambda-symbol
+create-symbol λ             λ-symbol
+create-symbol begin         begin-symbol
 
 \ }}}
 
@@ -885,6 +891,7 @@ parse-idx-stack parse-idx-sp !
     character-type istype? if true exit then
     string-type istype? if true exit then
     nil-type istype? if true exit then
+    none-type istype? if true exit then
 
     false
 ;
@@ -964,6 +971,9 @@ parse-idx-stack parse-idx-sp !
     ok-symbol
 ;
 
+: macro-definition? ( obj -- obj bool )
+    define-macro-symbol tagged-list? ;
+
 : if? ( obj -- obj bool )
     if-symbol tagged-list? ;
 
@@ -1007,7 +1017,39 @@ parse-idx-stack parse-idx-sp !
     drop compound-proc-type
 ;
 
-: application? ( obj -- obj bool)
+: begin? ( obj -- obj bool )
+    begin-symbol tagged-list? ;
+
+: begin-actions ( obj -- actions )
+    cdr ;
+
+: eval-sequence ( explist env -- finalexp env )
+    ( Evaluates all bar the final expressions in
+      an an expression list. The final expression
+      is returned to allow for tail optimization. )
+
+    2swap ( env explist )
+
+    \ Abort on empty list
+    2dup nil objeq? if
+        2drop none
+        2swap exit
+    then
+
+    begin
+        2dup cdr ( env explist nextexplist )
+        2dup nil objeq? false =
+    while
+        -2rot car 2over ( nextexplist env exp env )
+        eval
+        2drop \ discard result
+        2swap ( env nextexplist )
+    repeat
+
+    2drop car 2swap ( finalexp env )
+;
+
+: application? ( obj -- obj bool )
     pair-type istype? ;
 
 : operator ( obj -- operator )
@@ -1046,32 +1088,44 @@ parse-idx-stack parse-idx-sp !
 : procedure-env ( proc -- body )
     drop pair-type cdr cdr car ;
 
-: apply ( proc args )
+( Ensure terminating symbol arg name is handled
+  specially to allow for variadic procedures. )
+: flatten-proc-args ( argvals argnames -- argvals' argnames' )
+    nil? if exit then
+
+    symbol-type istype? if
+        nil cons
+        2swap
+        nil cons
+        2swap
+        exit
+    then
+
+    2over cdr 2over cdr
+    recurse ( argvals argnames argvals'' argnames'' )
+    2rot car 2swap cons  ( argvals argvals'' argnames' )
+    2rot car 2rot cons ( argnames' argvals' )
+    2swap
+;
+
+: apply ( proc argvals )
         2swap dup case
             primitive-proc-type of
                 drop execute
             endof
 
             compound-proc-type of
-                2dup procedure-body ( args proc body )
-                -2rot 2dup procedure-params ( body args proc params )
-                -2rot procedure-env ( body params args procenv )
-
-                extend-env ( body env )
+                2dup procedure-body ( argvals proc body )
+                -2rot 2dup procedure-params ( body argvals proc argnames )
+                -2rot procedure-env ( body argnames argvals procenv )
 
-                2swap ( env body )
+                -2rot 2swap
+                flatten-proc-args
+                2swap 2rot
 
-                begin
-                    2dup cdr 2dup nil objeq? false =
-                while
-                    -2rot car 2over ( nextbody env exp env )
-                    eval
-                    2drop \ discard result
-                    2swap ( env nextbody )
-                repeat
+                extend-env ( body env )
 
-                2drop ( env body )
-                car 2swap ( exp env )
+                eval-sequence
 
                 R> drop ['] eval goto-deferred  \ Tail call optimization
             endof
@@ -1110,6 +1164,11 @@ parse-idx-stack parse-idx-sp !
         exit
     then
 
+    macro-definition? if
+        2swap eval-define-macro
+        exit
+    then
+
     if? if
         2over 2over
         if-predicate
@@ -1132,13 +1191,34 @@ parse-idx-stack parse-idx-sp !
         exit
     then
 
+    begin? if
+        begin-actions 2swap
+        eval-sequence
+        ['] eval goto-deferred
+    then
+
     application? if
+
         2over 2over
-        operator 2swap eval
-        -2rot
-        operands 2swap list-of-vals
+        operator
 
-        apply
+        find-macro-proc nil objeq? if
+            \ Regular function application
+
+            2swap eval
+            -2rot
+            operands 2swap list-of-vals
+
+            apply
+        else
+            \ Macro function evaluation
+
+            2swap 2drop 2swap ( env mproc exp )
+
+            apply 2swap ( expanded-exp env )
+
+            ['] eval goto-deferred
+        then
         exit
     then
 
@@ -1216,6 +1296,9 @@ parse-idx-stack parse-idx-sp !
 : printcomp ( primobj -- )
     2drop ." <compound procedure>" ;
 
+: printnone ( noneobj -- )
+    2drop ." Unspecified return value" ;
+
 :noname ( obj -- )
     fixnum-type istype? if printfixnum exit then
     realnum-type istype? if printrealnum exit then
@@ -1227,6 +1310,7 @@ parse-idx-stack parse-idx-sp !
     pair-type istype? if ." (" printpair ." )" exit then
     primitive-proc-type istype? if printprim exit then
     compound-proc-type istype? if printcomp exit then
+    none-type istype? if printnone exit then
 
     bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
     abort
@@ -1459,6 +1543,7 @@ include scheme-primitives.4th
         read-console
 
         2dup EOF character-type objeq? if
+            2drop
             bold fg blue ." Moriturus te saluto." reset-term cr
             exit
         then