1 files changed, 134 insertions, 0 deletions
diff --git a/forth.js b/forth.js
new file mode 100644
index 0000000..83397c6
--- /dev/null
+++ b/forth.js
@@ -0,0 +1,134 @@
+function forth(print = console.log) {
+    const s = []; // the stack
+    const popNum = () => Number(s.pop());
+
+    const fs = {
+        ' ' : () => {},
+        '\n' : () => {},
+        '\t' : () => {},
+        '/' : () => {
+                const a2 = popNum();
+                const a1 = popNum();
+                s.push(a1 / a2);
+            },
+        '-' : () => {
+                const a2 = popNum();
+                const a1 = popNum();
+                s.push(a1 - a2);
+            },
+        '+' : () => { s.push(popNum() + popNum()) },
+        '*' : () => { s.push(popNum() * popNum()) },
+        '.' : () => print(s.pop()),
+        'peek' : () => print(s[s.length - 1]),
+        ':' : (initialIdx, tokens) => {
+            let localIdx = initialIdx + 1;
+            const fname = tokens[localIdx++];
+            const fnContent = [];
+            for (;tokens[localIdx] !== ';';  localIdx++) {
+                fnContent.push(tokens[localIdx]);
+            }
+            fs[fname] = () => {
+              exec(fnContent);
+            }
+            return localIdx - initialIdx; // numItemsSkipped
+        },
+        's' : () => print(JSON.stringify(s)),
+        'sum' : () => {
+          let total = 0;
+          while (s.length > 0) {
+            total += popNum();
+          }
+          s.push(total);
+        },
+        '(' : (initialIdx, tokens) => {
+          let localIdx = initialIdx + 1;
+          while (tokens[localIdx] !== ')') { localIdx++ }
+          return localIdx - initialIdx;
+        }
+    }
+
+    function exec(tokens) {
+        for (let tokenIdx = 0; tokenIdx < tokens.length; tokenIdx++) {
+          const token = tokens[tokenIdx];
+          if (fs[token]) {
+            const numItemsSkipped = fs[token](tokenIdx, tokens);
+            if (Number.isInteger(numItemsSkipped)) {
+              tokenIdx += numItemsSkipped;
+            }
+          }
+          else {
+            s.push(token);
+          }
+        }
+    }
+    return t => exec(t.split(/[ \n\t]+/));
+}
+
+
+if (window) {
+  const style = document.createElement('style')
+   style.innerHTML = `
+      #forthroot * {
+        background-color: #42456f;
+        color: white;
+	font-family: monospace;
+	font-size: 1.2rem;
+        box-sizing: border-box;
+      }
+      #forthouter {
+        cursor: text;
+        border: solid thin black;
+      }
+      #forthline {
+        width: 97%;
+        border: none;
+      }
+      #forthline:focus {
+        outline: none;
+      }
+      #forthresultsbox {
+        height: 90vh;
+      }
+      #forthresults {
+        margin-top: 0px;
+      }
+      #forthlinelabel {
+        padding-top:1px;
+        max-width: 3%;
+      }
+  `;
+  document.head.appendChild(style);
+  forthroot.innerHTML = `
+    <div id="forthouter">
+      <form id="forthform">
+        <label id="forthlinelabel" for="forthline" position="left">></label>
+        <input id="forthline" type="text" value="">
+      </form>
+      <div id='forthresultsbox'>
+        <pre id="forthresults"></pre>
+      </div>
+    </div>`
+  forthouter.onclick = () => forthline.focus();
+  const print = x => { forthresults.innerHTML = x + '\n' + forthresults.innerHTML; };
+  const m = forth(print);
+  forthform.onsubmit = () => {
+    print(`> ${forthline.value}`);
+    if (forthline.value !== '') {
+      m(forthline.value);
+      forthline.value = '';
+    }
+    return false;
+  }
+
+} else {
+  const readline = require('readline');
+  const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
+  const prompt = (query) => new Promise((resolve) => rl.question(query, resolve));
+  const m = forth();
+  (async () => {
+    while (true) {
+      const input = await prompt("> ");
+      m(input)
+    }
+  })();
+}